Moses Ludel

The 1991 axle's ring-and-pinion gear sets are likely the same as later axles. (Compare the part numbers in the parts listings.) The right side axle shafts within the front axle housing would be distinctly different between the 1991 axle with disconnect and any later models without axle disconnect. Moses

Maybe an update available from CasualMechanic here? It would be great to get an overview of how this conversion turned out... An MPI swap, if practical and manageable from a parts and labor standpoint, would provide some performance gains. In the late 'eighties, when GM stayed with TBI on truck engines, I attended a press launch of the '89 models. I recall a journalist colleague asking a GM engineer why TBI was in place instead of port injection like the GM performance cars. Ford at the time had MPI on its truck engines. The response was interesting, as this engineer was a motorhead and not just a corporate spokesman. His belief was that the use of an intake plenum with a central TBI unit actually produced more torque at a usable "truck" engine speed. I would argue that the uneven flow of air/fuel in any intake manifold with a central carburetor or TBI is obviously inefficient. When we played with the original "Mopar" EFI conversion* for the 4.2L Jeep inline six, the Electromotive fuel-and-spark system used a Holley TBI unit from an OEM Dodge V-6 application. That system was a big improvement over the BBD carburetor, though the best was clearly yet to come. By the mid-'nineties, Mopar latched onto factory off-the-shelf MPI from the 4.0L inline six and adapted that as the second generation Mopar Performance EFI Conversion for 1981-90 4.2L/258 retrofitting. It was a 50-State legal system and added nearly 60 horsepower to the 4.2L engine with no other changes. This was way beyond the gains of TBI. *The Electromotive system came into existence in the early 'nineties and is now virtually unknown by most Jeep inline six buffs. It was a bold attempt to improve the 4.2L engine without changing the intake manifold. The TBI had an adapter to the OE BBD two-barrel carburetor intake manifold. Unfortunately, the inline Jeep 4.2L six's stock intake manifold is very inefficient. Flow to the end cylinders is impaired, cylinders were inherently out of balance, and this engine begged for MPI. On a 2.5L TBI change to MPI, the gains would be proportionate, yet MPI with injection at each port and minimal intake runner length issues is clearly a major gain. As a retrofit, however, MPI from a 1991-up engine, swapped onto a 1987-90 model TBI engine, would have to offer a major incentive, something as serious as TBI parts no longer being available. This conversion is not for the faint of heart. It can take considerable time and thought to sort out each of the distinct differences between these two systems. CasualMechanic is enthused and objective. I'd really like his input here, as this task, in my view, is anything but simple. The wiring alone would keep one busy for some time. Moses

The switch for controlling the front axle disconnect is at the transfer case. It's signaling the 2WD to 4WD mode change within the transfer case. The transfer case shift triggers the vacuum shift at the front axle. The idea is not bad, although many of the parts involved will wear out or fail over time, especially all of the hoses, which will deteriorate at the underside of a 4x4. Given the number of Dakotas running around with this vacuum system (through the 1992 Dakota 4x4 models according to the parts listings), it would make sense to encourage Posi-Lok to build a manual shift kit for this application. I'd suggest contacting Posi-Lok. Share this forum topic thread and also note the other forums where owners are clambering for a solution. As a stop gap and immediate solution for your 1991 Dakota, see if Posi-Lok will determine which parts can be reused from the OEM Dakota actuator assembly and blend with Posi-Lok controls. Like Biggman100 shares, there may be a way to mate off-the-shelf Posi-Lok pieces with your existing parts to make this work. If the vacuum diaphragm is the issue, another alternative is to identify the vacuum diaphragm maker (look closely at the canister). See if this Dakota diaphragm has any other application in the industry. The canister may be available as a replacement part if that's all you need. There are even ways to rebuild or retrofit a canister...For other hard parts, the Jeep versus Dakota schematics and parts listings that I provided might help. If the shift fork is unique to the Dakota, that's another story. Another approach, if all other parts are the same in a later Dakota front end, including half shafts, flanges and so forth, is to get a later Dakota front axle center housing assembly with the same axle ratio as your current truck. (Ring-and-pinion gears could be swapped if necessary.) The later non-disconnect axle center housing and axle shafts assembly would eliminate the disconnect problem without the need for a Posi-Lok. Make sure all other parts are compatible and that these later front ends are identical to the 1991 with the exception of the vacuum disconnect feature. Biggman100 may have insight here. Some scrutiny of Dakotas at recycling yards could turn up answers, too. For comparisons, here is the front axle and axle shaft arrangement on a 1994 (essentially 1993-up) Dodge Dakota 4x4 without an axle shaft disconnect: 1994 Dodge Dakota Front Axle.pdf Note: What you need to confirm is that the later Dakota 4x4s without the front axle disconnect are entirely the same in other ways. Make sure that the only change in the later Dakota is a front axle housing without a disconnect feature that uses a one-piece right side axle shaft. If this all works, you can strip out the vacuum maze and cap off the transfer case vacuum fittings and switches with vacuum caps. Confirm that you still have a signal for the dash gauge 2WD/4WD mode change lamp. Explore the feasibility of this simpler solution: Like the 1991 front axle, the later Dakota front axle uses an outer housing end seal for the axle shaft. If the later right side axle shaft and later axle shaft bearing and seal will fit your 1991 axle housing, consider using a later non-disconnect right side axle shaft in place of the OEM two-piece disconnect right side axle shaft. Make sure the later (1993-up) axle shaft's splines, the later axle housing outer seal and the later axle shaft outer bearing will work with your 1991 front axle housing. The overall axle shaft lengths and half-shaft drive flanges must match, too. If the later right side axle shaft will fit and seal properly, you have "converted" to a non-disconnect front axle. The Actuator assembly could be eliminated completely, you can make a cover plate for the actuator hole in the housing, install a new gasket or use RTV sealant, and mount your new homemade cover plate. A piece of 0.120" steel sheet metal would work well for the cover plate, easy to cut, form and drill the mounting holes. If all this works, strip away the vacuum maze and make sure you still have a dash signal lamp for 2WD/4WD mode. Please share your findings here, and if this will work, document the installation with photos. Many reading this forum topic would benefit from the photos, fit-up steps and part numbers involved! Biggman100, I'm curious what the parts view in the right photo represents. The vacuum canister and shaft look new, the housing and fork, too. Are these Posi-Lok parts for a full-size Ram or a Jeep? Moses

Please clarify which Jeep model you have...There are a variety of OE and aftermarket options here...Welcome to these forums, WrangleDangle! Provide more details, you'll get a useful response. Moses

Hendogg...I'm pleased to see you join and participate at these forums...Welcome! Thanks for sharing these valuable insights for Dakota truck owners interested in a hemi V-8 swap! Moses

Pleased to have you join our forums, fnordo. Glad you've "met" Biggman100 and broadened the discussion on your '91 Dakota front axle disconnect motor/actuator assembly. For openers, the parts involved with this front axle disconnect make for a very "busy" system. It's interesting that the Dakota still uses the disconnect in 1991, and this could have something to do with the IFS front end and the axle half-shafts. By 1990, the Jeep XJ Cherokee had discontinued the use of a disconnect at the front axle, although the YJ Wrangler stubbornly adhered to the setup. Here is the complete disconnect system for the Dakota 4x4, referred to as the "N5" model. One page in this PDF has "D5, D6 and D8" model references, and these are the full size trucks, not the Dakota: 1990-93 Dodge Dakota Front Axle Disconnect.pdf If anyone is curious why there is no parts interchangeability between the Jeep 4x4s and the Dodge Dakota, here's my take: Unlike the full-size trucks and the Jeep models, the Dakota uses a Chrysler 7.25" front axle. The Jeep lighter 4x4s since WWII have used the Spicer 25 and 27, and later the Dana 30 front axles. Full-size Jeep J-truck and Dodge trucks also use Spicer/Dana axles, although these would be the bigger Spicer and Dana 44 type front axles, and even the larger Dana 60 type on heavy duty chassis. More recently, Dodge Ram full-size trucks have used the AAM front and rear beam axles. While Jeep and full-size Dodge trucks have each used Chrysler type rear axles, the Dakota 4x4 uses a Chrysler axle at the front as well. That leaves the Dakota with a unique front axle disconnect motor or "actuator". Here are 10 components with OEM part numbers for the Dakota front axle disconnect vacuum motor assembly. (See the PDF for more parts and illustration details.): 1) 04169634 SWITCH, Hub Lock Indicator (Blade Conn.) 04289880 (Pin Conn.) 04338554 GASKET, Switch 2) 04338654 VENT, Fitting 3) 04338648 COVER, Disconnect Housing 4) 04338570 GASKET, Cover 5) 181088 SCREW, w/Washer 6) 04338578 MOTOR, Vacuum Disconnect 04338792 SHIELD, Stone 1990 53008828 1991-92 7) CLIP, E-Type (Serv. w/Motor) 8) 06023878 1 CLIP, E-Type 9) 04338573 1 FORK, Shift w/Pads 10) 04338589 2 PAD, Wear Now we'll compare the actuator found on Jeep XJ Cherokee and YJ Wrangler front axle disconnect systems. These were found on 1987-95 Wranglers and the Cherokee from '84 until Chrysler/Jeep eliminated the actuator. Note on the Jeep YJ Wrangler that there were years when the axle has no front axle disconnect system or actuator. The XJ Cherokee shifted to this non-disconnect front axle approach by 1990. For whatever reason, the Dakota 4x4 kept the front axle disconnect system with the vacuum actuator motor. Note: Wondering why this elaborate vacuum disconnect system was there in the first place? The whole point to front axle disconnect is that by splitting one axle shaft when the system is in 2WD, the drag from the front driveline and axle differential case/ring gear assembly is eliminated. (I've given thought to this, and the net result is that the front differential side gears and pinions get a major workout with this design, spinning twice as fast as normal while the ring gear, differential case and front driveline remain stationary.) The disconnect takes effect while no power flows from the transfer case to the front axle. One objective is reduction of driveline and differential/ring gear drag or frictional loss...There would be no drag if Jeep and Dodge had simply kept the earlier style full-floating front axle wheel hubs with free-wheeling hubs at the outer ends. Unfortunately, this was the era when marketing took precedence over sensible design: It was assumed that consumers did not want to get out of the vehicle to turn a free-wheeling hub. There were automatic locking hubs used by OEs and available in the aftermarket; however, these tended to be less predictable and were not trouble-free. Chrysler elected to use axle shaft splitting with a vacuum disconnect mechanism rather than stick with full-floating front axles and encouraging the development of better automatic locking hubs. One drawback with automatic locking hubs is that they remain locked after shifting back to 2WD mode until the vehicle stops completely and is backed up. Here are the Jeep YJ Wrangler parts. Compare the design, layout and part numbers. See what, if anything, will interchange, as the Jeep application parts should still be available. Otherwise, either the Posi-Lok (if that company wants to get involved) or piecing together used parts to restore the OEM Dakota system may be necessary. Sounds expensive if you need to buy a complete Dorman actuator just to replace the vacuum diaphragm: 1987-95 YJ Wrangler Front Axle.pdf For a quick overview, here are the front axle disconnect actuator/motor part numbers from the Jeep YJ Wrangler parts listing: 1) 83503113 1 MOTOR PACKAGE, Front Axle Vacuum 2) J8133708 1 CLIP PACKAGE 3) 83504813 1 COLLAR, Axle Shaft Shifter 4) 83503695 1 FORK, Axle Shift 5) J8133618 1 RING, Snap 6) J8133619 1 RING, Snap 7) J8133709 1 GASKET, Cover 8) 83500195 1 COVER, Axle Shift 9) J8133624 4 WASHER 10) J8133623 4 BOLT 11) J8133620 1 O-RING 12) SEAL, Rt. 83500199 1 2.290" 83503504 1 2.125" Compare the part numbers. Look at the schematics. (Zoom-in for details on the PDFs.) We'll go from there... Moses

You're very correct in your assumptions, smokes3456! I've shared that when we make any of these changes or upgrades, there should be a purpose. To be technical, you will actually get better fuel efficiency at 2,100 rpm with the Hypertech solution than with your stock tuning program at that same 2,100 rpm. Here's the reasoning: If the stock torque peak (currently 1600 rpm on your HO 5.9L) begins to drop by 2,100 rpm, then the engine is not as efficient as it could be at that rpm. The program I installed not only raises the torque peak rpm, it also increases the torque output at that rpm. So I'm gaining both additional torque and the ability to operate the engine at a higher rpm. This higher rpm is desirable when I'm not towing. I've actually geared the truck for the "discipline" of towing at 65 mph, which is 1980 rpm with the current gearing (4.56) and tire diameter (around 584 revs/mile). When not towing, however, I do want to go 69 or 70 mph, the posted local interstate speed. My current engine rpm at these speeds is approximately 2100-2150 rpm. Note: Often overlooked with tire and wheel changes is the inaccuracy of the revs/mile. My BFG All-Terrain tires have an advertised revs/mile of 601. On the 9" aftermarket rims, to get my speedometer correct, I had to factor 584 revs/mile. This tire, though called a 35" (really 34.6" at 601 rpm), is actually stretching to 35.5" on this rim. Next tire change, I may try a true 36.5"-37" diameter tire if the chassis lift will allow it. This would drop revs/mile to 560-568, and engine rpm would drop correspondingly. At 560 revs/mile (true 37" diameter), 69 and 70 mph would be 2,026 and 2056 rpm. There's no free lunch. We're striving for optimal fuel efficiency for an intended or desired road speed and engine rpm. In my experience, maximum fuel efficiency is always around the torque peak rpm. As a footnote on this, Cummins actually wants to see a commercial truck with this 5.9L ISB engine spinning 2100 to 2400 rpm for best economy and performance. This begs the question: What is the tuning program in these commercial 5.9L ISB applications that can lug up to 50K gross vehicle weight? My guess is that the tuning would be very close to the Hypertech Max Energy program, which Hypertech indicates is "tow friendly". Regardless of engine tune, the pyrometer is a great idea. Pulling more horsepower out of a diesel engine, whether stone stock tune or built for tractor pulls, is always a matter of shoving more fuel into the engine. And this results in a heat rise. Heat can damage, and using a pyrometer is just as important as watching the tachometer! I plan to install a pyrometer before we begin trailer towing on a regular basis. Our 5.9L is now "just broken-in" at 140K conservative load miles. Only 12,000 or so miles have been trailer pulling, and I am considerate of the powertrain when towing. (I do have a pyrometer of sorts: My heavy equipment operating background governs the pressure at my throttle foot.) I plan for this truck to last a very long time, even with the increased piston travel I created with the lower (numerically higher) axle gearing. Despite that increased piston travel, the gearing does decrease load on the engine. As I noted, a good compromise or "rpm tune" would be 36.5" or even 37" (true to size) tires to get the rpm down some with these 4.56 axle gears...Otherwise, 4.30:1 gearing would be optimal with the current tire diameter. For your purposes, I would share that the best fuel efficiency I ever got was stock and with 3.73 gears, using the 0.69 overdrive in the 48RE automatic transmission, and running stock wheels and tires. That was between 65-69 mph, the tip-over point was 70, after which I would "pay for the privilege" of driving faster and using more fuel. Hypertech told me that fuel efficiency goes up with its programming, and this might be a worthwhile gamble; the torque even increases at the stock torque peak of 1,600 rpm and continues to increase to 2,100 rpm. See the dyne chart at the magazine article... Your current fuel efficiency is a true credit to your driving technique. I cannot imagine any modification that would get you better than 26 mpg. Even the 24.5 mpg is excellent. There are some with our trucks who cannot muster 20 mpg stock, and this can only be due to driving technique. When stock, my truck's peak mileage was consistent with yours, and the truck is an SRW with a Quad Cab, likely lighter than your DRW truck. Moses

Jeff...From what you shared about the color of the fluid, the transmission sounded due for a fluid change and filter. You're good at assessing a vehicle, this one seems like "good mileage"... great father/son project and place to start! Glad nothing ominous turned up in the transmission oil pan. This should be an accurate read, the fluid had been in there quite a while...You'll go over the rest of the truck... Moses

Smokes3456...I did the Hypertech Max Energy program for exactly the reason you want: peak torque at a higher rpm. Take a look at my article on the magazine site and see the results. This is the only modification I've made. There are many more (i.e., costly) solutions and upgrades, this was my simpler initial approach: http://www.4wdmechanix.com/Hypertech-Max-Energy-Power-Programmers-for-Jeep-4.0L-and-Dodge-Cummins.html After reviewing the torque gains and my comments, let's pick this up again... Moses

The torsion bars could be worn, but they are weight rated in any case. The plow might be too much even for new torsion bars. In either case, you may be able to adjust the torsion bars/ride height, this is often a part of alignment (ride height) on torsion bar vehicles. You would be adjusting for a plow that might only be temporary. When the plow comes off, the front end height would "leap" up, and you'd be resetting ride height. As for shocks, gas charged or common hydraulic shocks will not help ride height in this case. Air shocks would, but I'm not trusting of air shocks for maintaining the height of a vehicle as you describe it. If the front end height is dependent on air shocks and a shock fails, this could be a safety hazard on the highway... How much did the front end droop? Moses

J-F...Pleased that you identified the problem and found a suitable engine replacement. Busy as you are this time of year, it's important to have a reliable Jeep! Keep us posted... Moses

All good points, Biggman100!!! In 1996 at age 47, I volunteered for the Tread Lightly USA/UK Team to compete in the Land Rover Trek competition. Though this was a mini-Camel Trophy event condensed into one very long day, the strain could have severe repercussions for an undertrained competitor. I had the good sense to focus on cardio fitness, and four months before the event, I began training. My "conditioning" has never been way off, and I'll get into that point after sharing my training regimen for Land Rover Trek... My first approach was purchasing a Polar Heart Rate Monitor. I got the training book that came with this device, a fairly new concept at the time, and followed the use recommendations precisely. That included one very important factor: Always train cardio from your current condition and not some "illusion" about your glory days. For me, this meant not comparing my condition at the time to my days as a high school football player, adult construction laborer, heavy equipment operator, gym member (which I did for many years), my earlier martial arts training or those mountain climber/hiker days. I was writing books and doing magazine assignments in 1996, working on vehicles at my shop studio, and none of these functions qualified as regular "cardio exercise". The regimen with a heart rate monitor is simple: stay in your correct heart rate zones. This means the device, much like a tachometer, will help you either increase or decrease your exertion level based upon your real time heart rate. Initially, a walk could get you in the zone. Over time, the exertion required for cardio training increases. A brisk walk, a light jog, soon you are pushing to stay in the zone. Interval training was my end game, watching constantly for a reasonably quick "recovery" to normal heart rate when I stopped exerting. Never sit down after a workout, always keep moving as you bring your pulse rate down. Eventually, actually in only six weeks or so, my heart "muscle" was once again attuning to a cardio workout. For training at a more athletic level, I held to the 120-140 beats zone, with a gradual warm up before holding in this range. As for your "right" heart rate, this must be determined by the age formula and your overall condition. Caution: Always make sure your heart is up for training in the first place, get a physical from a qualified physician, and follow the age formula for setting your training heart rate beats. Start out slower, work up gradually, and don't go beyond the zone. Pushing beyond the zone will only cause fatigue and delay your conditioning. At 65 years of age, I can do 20 minutes on a training exercise bicycle at the gym with a target of 120-135, a bit higher than others my age. At 47, my maximum heart rate, once in condition and able to test myself without risk, was 191 beats a minute, which is normal for a 31 year old. This state of condition is from exercising and being active over a lifetime and also reflective of very fortunate genes. We'll see how far this takes me, I never take my health and fitness for granted, and if I don't hold to my end of the exercise bargain, my heart genetics will be for naught. As for my lifetime condition, I was a very active child. We camped and hiked at high elevations, I played high school football, ran track and worked after school and summers, including heavy lifting at a Sierra fishing resort as the garbage collector, hoisting and dumping trash drums of fish guts over the rails of a vintage Chevy flat bed truck. As an adult, beyond the workout from automotive/truck mechanics, I remained outdoor active and worked as both a construction laborer and heavy equipment operator before heading to the University of Oregon at age 28 with wife and kids. At the U of O, I took PE conditioning classes and studied martial arts, which I continued for several years. When I graduated in 1980, the only available job at Eugene/Springfield was the working foreman at a commercial big rig tire shop. I was grateful to have worked hard physically to that point, it helped with the tire busting. I kept up gym memberships through a variety of work stints and career moves after college. For me, outdoor activity included hunting and fishing, hiking and such. I've done my share of rock crawling in 4x4s, personally and professionally, and the four-wheeling thing is no longer just "driving around in circles or over rocks". Today, aside from enjoyable family "destination" four-wheeling, I'm as happy on the ground with a video cam along the Rubicon Trail, traipsing over boulders and up granite faces at 7,500-plus feet elevation. For me, the physical workout is as invigorating as driving the trail. As for conditioning, I highly recommend a gym environment unless you either cannot afford it or are tremendously disciplined about home exercise equipment. We have owned a list of home equipment that all went down the road over time, usually after a final stint as a clothing rack. For me, anyway, the gym works, I'm good about sticking to a regimen—once I get suited and headed in the direction of the gym. Often, it's that initial push-off resistance that's harder than the exercise routine! My advice to weekend warriors and those out of shape who have a chronologically older body with an 18-year-old zest for activity: Get a heart rate monitor before launching your exercise program. Use the monitor like a tachometer, and don't over-rev your heart! If you initially have to crawl in order to hold your heart rate in the correct zone (use a guide here, do not improvise on your training heart rate beats), that's okay. In training this way, you'll get fast gains without stressing your cardio system. The heart rate monitor is cheap insurance that enabled me to compete effectively at the Land Rover Trek. That included running in hills, pedaling a bicycle uphill and through a creek bed in red Georgia clay mud, ropes exercises, canoeing and winching activities, all under the demands of a stopwatch! The easiest and least physically demanding part was driving the 4WD Land Rovers on an off-road course. Keep this in mind—even if your 4x4 is in great shape, you made need to do something physical for yourself or others! As I've mentioned repeatedly, my dirt motorcycle riding is partly an excuse to stay in better condition. I ride motorcycles in the backcountry as an adjunct to training and the gym, not in place of conditioning. The demands of dirt motorcycling, both physically and mentally, can be extreme. I take on this responsibility under only one condition: being in decent physical shape before throwing my leg over the saddle...Riding is an enhanced, five-muscle group form of additional exercise that I happen to enjoy. Moses

forman...Jeff, the 700R4 and 4L60 have an extra low first gear ratio. These transmissions were developed to offset ridiculously tall (numerically low) axle ratios in emissions cars and light trucks. In the truck applications with reasonably low (numerically higher) gearing and stock diameter tires, the upshift to 2nd is noticeable, feeling much like the older THM350 or 400 transmissions. Still, the shifts should be smooth with this unit unless you have your foot in the throttle. That will hold back (detent) the shift, causing a harder upshift due to the increased (throttle) pressure. To provide some insight, here are the gear ratios for the 700R4 and 4L60: First - 3.059:1 Second - 1.625:1 Third - 1.000:1 Fourth - 0.696:1 Reverse - 2.294:1 Upshift road speed would be governed by the axle ratio, though you can tell from engine sounds whether the transmission is hesitating or holding in a lower gear. You'll sense the difference. As for slipping, this is again a noticeable engine revving sound that makes you instinctively back out of the throttle! Shifts should be distinct, though like the later transmissions you mention, there is typically a softer shift feel. Softer does not mean lag or slipping, though. At light throttle, there will be no harshness but rather a quick and smooth upshift to the next gear. Lag is caused by either holding in the lower gear or slip. Holding in a lower gear results from throttle pressure issues, incorrect kickdown signals or a valve body malfunction. Overall, the 700R4 should not feel much different than a THM350 or THM400, although the ratios are different. Again, unless the truck has a taller axle ratio, you will notice the lower first gear ratio. You might check the axle ratio tag on the axle and also note the tire size/diameter. Are you flushing the converter with that fluid and filter change? Is this being done at a commercial shop with a flushing machine? Ideally, before flushing, you want to check the content in the transmission pan for any metal, nylon, friction material or other signs of wear. Some of your great pictures would be worth viewing... Moses

Hi, Jeff! Best at the Holiday Season, good to get your post...The 1991 Chevrolet C1500 automatic transmission would be a 4L60, not the 4L60E electronically controlled unit phased into production in 1993. Your code is a 4L60 (GM RPO MD8), essentially an evolved 700R4. You will find my comments and details on the 700R4 in the book, which will be applicable to your 4L60 transmission. In this iteration, the transmission is refined and updated for reliability. I trust the book will be a good read for your son and furnish useful insights. A factory workshop manual would be advised for major unit work, used books are out there in both complete editions and also as "Unit" books that detail the transmission and other unit repairs. I can help with any advice, schematics, etc. My library is extensive on all GM automatic transmissions back to 1941! I have rebuilt the 700R4 and equivalent transmissions. They have a lot of components and must-follow assembly sequence concerns. If you decide to tackle the 4L60 as a father/son project, I believe you will be successful as in your other recent projects. One "specialty" tool required is a universal AT clutch spring compressor available through K-D and others. You can improvise beyond this tool...The rebuild kits are not expensive, and hard parts damage can be avoided if the rebuild takes place early enough in the wear cycle. For those who have rebuilt an automatic transmission before, this is an "accessible" though very busy transmission. As for a "health check", I like to run proscribed pressure tests to make sure circuits are intact and functioning with a full flow of pressure. Gear applies and other direct results are helpful. There are a variety of air pressure checks for that approach. If the 4L60 is not slipping or showing signs of a torque converter issue, the complete unit and converter flush and fill with a new filter can be restorative. With the coloration of fluid, I would do the converter flush along with the unit fluid change plus add a new filter. Use GM recommended fluid, do not get creative at this mileage with exotic or expensive fluid. Make sure the transmission is fully functional before upgrading anything. Check linkages and the signal switches for kickdown, as these boost pressure and can sometimes create issues like the harsh downshift you describe. Harsh shifting can also be sticky or maladjusted pressure switch signals, line pressure too high or pressure regulator issues. I can be more specific once you've done preliminary cleanup of the unit. If that does not "cure" the maladies, share specifics about when the unit shifts poorly or malfunctions on any level. We can troubleshoot from there. Or, if you'd rather plunge into diagnostics before spending cash on flushing and a filter, we can address drivability and shifting symptoms now...Your call, Jeff. Moses

Good news...This summer will be the supreme test, but at least you're through tinkering on this Dakota for a while...Next? Moses

Spdljohn...The tub looks great, David! You'll both be very pleased over time that you took this approach. Cleaning the Jeep after a muddy trail, peace of mind around corrosive winter roads, salt air, whatever you throw at these tubs, you've got a Jeep CJ tub that will last the life of the vehicle. For those living at the Rust Belt, this is the tub cure. The bottom side is at least as important as the interior and bed. Perforation rust usually begins at the underside on an AMC-era CJ Jeep. What did the Line-X outlet say about the seal and prime on that tub from the Philippines? From the photos, it looks okay. Still best that you sealed the tub with Line-X liner. Like that color, too!!! Moses

Good idea, all around...The chain system is great for vintage models with through-the-floor pedals, light years ahead of the OE cable linkage. Hydraulic linkage can be fitted fairly easily with fabrication of a hydraulic slave cylinder mount, but you're right, the cost of a hydraulic master cylinder, a slave and hose or tubing adds up. You'd also need to find pedal linkage from a four-cylinder model with a master cylinder. By sheer coincidence, each of the '80s CJs that I used for projects had four-cylinder engines originally—and stock hydraulic clutch linkage. I modified these hydraulic systems to work with OE six-cylinder clutch and bellhousing layouts. An Advance Adapters bellhousing (stock 4.2L replacement) has a provision for the slave mount. I was fortunate in that the clutch pedal setup, master cylinder and slave were usable. One project had the Iron Duke four-banger, the other an AMC four. Actually, these were both good engines, just not "magazine material". You'll be fine with your planned heim joint arrangement. Many Jeep CJs with your clutch linkage have made it over the Rubicon Trail, though for the sake of your happy home, I'm not suggesting that you "test" your pristine restoration job on such trails...Tennessee and S.E. clay mud will be plenty. Once you're satisfied that the clutch return spring at the release lever will keep all of this aligned and in place, it should work well. You do need the return spring to assure that the clutch release (throwout) bearing is not riding on the clutch cover fingers when the clutch pedal is released. A general tip for AMC era CJs: Make sure the clutch pedal height from the floor is adjusted properly. That height assures adequate linkage travel. Moses

This late CJ mechanical clutch linkage is "questionable" as you share, actually it's notorious. In the late '80s, I was on assignment for OFF-ROAD Magazine at Arizona, shooting still photos of a valued advertiser's heavily modified Jeep CJ. He had your linkage on his V-8 upgrade powered Jeep. At the owner's insistence, I perched to catch photos of the Jeep "leaping" over a high berm, a maneuver that made magazine covers in the day—and even now. Not sure what the "message" is here. As the Jeep landed, the clutch link jumped off the release arm and left the CJ with no way to operate the clutch. Fortunately, the photo was much to the owner's liking, as it was the last pic in the set! Advance Adapters has been solving clutch linkage problems on Willys and Jeep vehicles from the MB WWII model forward. I've used several of their solutions to much satisfaction. They also have clutch links with a half-ball and a universal threaded stem that could possibly help with your current linkage. The stem would pass through a hole you drill in the release arm end, and the stub would prevent the linkage from jumping out of the arm end. You'd still use a return spring. I'm not thrilled with this approach, as you're drilling a relief hole in a stamped, not all that heavy duty release arm. For those interested in this issue, I'm sharing the schematic and OEM parts layout. I have included an example of the factory hydraulic clutch linkage used on the 2.5L Iron Duke GM fours (used to 1983), diesels (export only) and the RHD 4.2L export models. This RHD 4.2L model's hydraulic linkage setup uses the same release fork as 60Bubba's CJ-7 LHD 4.2L model—compare the part numbers. AMC 2.5L engines, introduced in 1983 and not included in the illustrations, use hydraulic clutch linkage but have a cross-housing release arm that does not operate in the same direction as the CJ 4.2L LHD factory release fork. The cross-housing arm is similar to the clutch linkage arrangement on the XJ Cherokee 2.5L fours introduced in 1984. The last illustrations are the busy mechanical linkage like on 60Bubba's CJ-7. On any of these PDFs, you can zoom-in on the illustrations or part numbers for clarification: 1981-Up Jeep CJ-7 Clutch Linkage.pdf The best solutions involve hydraulic linkage and eliminate the plethora of mechanical linkage parts...Before plunging further, check out the Advance Adapters catalog online (click here to http://www.advanceadapters.com). Consider a call to 1-800-350-2223 and connect to the helpful, Jeep-friendly tech line. Advance Adapters is located at Paso Robles, not too far from your current home, 60Bubba. Moses

Wheel offset is always a concern...When you get to that point, choose a wheel with the correct width and offset for your Dakota's front end geometry. Scrub radius and steering axis come quickly to mind...The photos are very helpful, Biggman100! Moses

Megatron...The official "word" is at the Valvoline Q&A page: http://www.valvoline.com/faqs/motor-oil/racing-oil/. Take a peek, you'll gather that zinc-phosphorus is a powerful anti-friction and sheer resistant compound. Zinc is zinc, though the oil additive version is chemically compatible with the rest of the oil additive package. There is a note about compatibility in Valvoline's comments, it is important to make sure the oil and additives will not react adversely. That's why I turned to Lucas' break-in additive with Zinc Plus and did not get creative. No sense becoming an oil engineer or modern day alchemist. I have enough balls to juggle! As for how long to leave this zinc additive in place, Lucas says 1000 miles, and I'm sure that's for a reason. Hamilton's comments sound logical. The main issue is break-in of the camshaft lobes to the lifter bases. This sets up an interface pattern that will last for the engine's lifespan. Builders know that you never mix the lifters when disassembling an engine and reusing the camshaft and original lifters! I'm curious about your camshaft change and grind, your motives and objectives here, and why you went to these lengths. What's the driving environment? Sounds like a new topic post brewing here! Moses

How would the moon cap wheels work with the Dakota 4WD front wheel/hub design? Would the wheels and caps clear the axle stubs and flanges? There are examples of Jeep flange drilling at our CJ Jeep forum: http://forums.4wdmechanix.com/topic/106-ford-88-rear-disc-brake-conversion-on-1986-jeep-cj7-dana-44/. LastCJ7's posts may provide some ideas. The stock CJ-7 had a larger, 5 x 5.5" wheel sizing. The Explorer 8.8" rear axle is the swap-in that led to his choice of resizing the flanges. Moses

The Dakota has an odd wheel bolt pattern, Biggman100. Is there a popular import truck with a metric sizing that matches this U.S. bolt pattern? Toyota FJ40 and pickup wheels were interchangeable with common Chevy 6-lug in the day. If there's a popular import interchange, maybe a wheel for that application meets your tastes. Some re-drill the hub and axle shaft flanges, though you'd have to find drums with the same locating center hole size, brake drum/shoe sizing, offset and so forth. Same with the front rotors. I'm not keen on the idea of drilling rotors or drums, though many do this, I see it a lot in the Jeep/Ford Explorer and other hybrid axle swap arrangements. Another possibility would be a change of front bearing/hubs and rear axle shafts to a more common Jeep sizing in 5-bolt. Confirming parts interchangeability would be required here. The rear axle shafts would be the same scenario. If you have an 8.25" Chrysler rear axle or a Dana 44, there could be a direct axle shaft and drum replacement if you can find an axle shaft length that is the same...Just a thought. You'd have stock and common Chrysler parts with this approach. Other members, please jump into this discussion. Share your experiences and solutions. Moses

The main concerns when starting a diesel engine in cold temperatures are oil viscosity and the stress on crankshaft bearings. In the lifespan of a properly maintained engine, over 95% of the engine's bearing wear will be attributed to cranking and start-up. This applies to both diesel and gasoline engines. Any reduction in start-up stresses and loads will extend engine life and performance. Your oil choice is a good place to begin. In recent years, there have been several breakthroughs in oil development. Since viscosity choices must match the climate, the latest crop of "winter" oils from major commercial oil producers is noteworthy. I've been running 15W-40 Delo 400 year round in the '05 Dodge Ram Cummins 5.9L, and the engine uses negligible oil between changes. (The most that's ever been consumed was 1/2-quart in a 5,000 mile change cycle that included towing an 8,000# trailer up I-8's long 6% grades from San Diego to Anza-Borrego and back.) The engine does not leak, a major tribute to modern design seals at the crankshaft and timing cover. Oil pressure has always been respectable and remains the same today as when the Ram 3500 left the dealership lot over 140K miles ago. I have recently considered changing to 5W-40 Delo 400 or equivalent diesel oil for winter protection. Rotella, Ursa, Delvac and Delo are each excellent commercial/fleet products. I would run this oil year round. The 5W cold flow can dramatically reduce cranking stresses on start-up when the truck parks away from its block heater in the winter. Delo in this viscosity is a synthetic base formulation, which does increase the cost. Here's a link to Delo oil products. Note that Texaco's "Ursa" label is also in the listed oil offerings: http://www.deloperfo...ngine-oils.aspx Short drives with a diesel, in the winter especially, are torture. My office is around two miles from the I-80 onramps. In the winter, when below 45 degrees F, if I'm headed to Reno on a cold day, I can be three miles down the interstate before the engine reaches full operating temperature...and that's with the block heater plugged in the night before! I rely on the additional 27 miles of interstate cruise to disperse the cold start/warm-up diesel fuel particulates in the crankcase. Note: We get plenty of sub-freezing weather in the winter, and I always use the factory block heater before a planned trip, allowing 12 hours or so of coolant warming before start-up. I installed a block heater on the 4.0L Jeep Cherokee gasoline engine and use that heater every night in the winter, as this is our daily driver. A block heater is a must for any diesel vehicle parked outside. 45 degrees F is my magic temperature for plugging-in the block heater before a run. With a switch to 5W-40 oil, I might change the block heater plug-in to freezing temperatures—or maybe keep with the 45 degrees F practice. The heater works nicely with the block warmed first! I also use a battery maintenance device nightly in the winter. On the Ram truck that parks for extended periods, the device remains connected continuously. A Battery Tender or CTEK charger works fine for this purpose. The CTEK has many additional features. For more information on the CTEK charger, here is the link to my article and HD video on the CTEK: http://www.4wdmechanix.com/CTEK-Battery-Chargers-for-Battery-Maintenance,-Restoration-and-Storage.html. Note: A Battery Tender has kept the OEM Mopar batteries in good condition since we purchased the Ram 3500 new, and that was 10 years ago! I attribute this to the battery maintenance device, which stays on when the truck parks in the winter or even in the summer if the vehicle will set for some time. The new CTEK charger has a Reconditioning de-sulfate function that I will try on these two batteries, disconnecting their cables first and isolating each battery. 10 years of service is remarkable life for diesel batteries! These measures provide the least load on the engine at start-up and provide the best method for getting oil to critical bearing parts. If your Dodge Ram Cummins parks in a cold climate, consider use of the block heater and battery maintenance device. Select the right viscosity oil for your climate and driving demands. Moses

Megatron, I always enjoy your topic posts and replies, many members and guests benefit from your valuable and thoughtful questions! This question begs attention... First off, let's address engine loads for a moment and the role of motor oil. Oil maintains a lubricating film and barrier to parts friction, in particular metal-on-metal parts like flat tappet lifters against the lobes of a camshaft. To put this into perspective, the load on a moving engine part is measured in pounds-per-square inch of actual contact between the parts. It just so happens that the base of a new flat tappet lifter (solid or hydraulic) is convex, not flat. This means that the contact surface between the lifter base and camshaft lobe is far less than the lobe's width. Actually, the contact point is relatively small. The lifter has a big job to do, raising the pushrod and rocker arm to compress the valve spring(s) under great force. Coupled with the relatively small and convex contact point between the flat tappet lifter base and the camshaft lobe, the lifter base's pounds per square inch (psi) load is extreme when the valve spring is compressed. How extreme? According to a Sealed Power reference that I've quoted since the 1980s, the psi load at the contact point between the lifter's convex base and the camshaft lobe is equal to the "weight of a locomotive". Sealed Power tossed out the figure 233,000 pounds per square inch of force. Today online, you will find consistent references from 140,000-240,000 psi. For curious motorheads, this figure would be governed by the valve lift (height) and the valve spring tension when the spring(s) compress at full valve lift. The rocker ratio also fits into this relationship and load calculation. So, given this extreme load, which Sealed Power indicated flatly as the highest singular load within an engine, imagine the demand on engine oil. We all know what metal-on-metal will do, and the oil has to keep the lifters from destroying the camshaft lobes. It's easy to understand how a GM epidemic of flat tappet camshaft failures on small-block V-8s in the 1970s and early '80s led to the added expense of using roller lifters in these "emission" small-block engines by 1986. Roller lifters became cost effective in the long run...They also reduce friction and valvetrain stresses. To protect this metal-to-metal contact, engine oil must provide a strong film and act as an anti-friction agent. For those unfamiliar with engine plain bearings like rod and main inserts, these parts do not ride on the crankshaft—they ride on a pressure-supplied oil film between the bearings and crankshaft journals. It's not the oil pressure that keeps these parts separated, either. Pressurized oil simply provides a continuous supply of oil that keeps the bearing's clearance space filled with oil. It's the oil itself that keeps these parts separated. In the case of a lifter, the oil that splashes or sprays onto the lobe and lifter base simply coats these parts. The oil's film strength and sheer resistance keep these metal parts separated to prevent the pieces from tearing each other apart. Historically, the best additive for protection has been zinc. To put zinc's importance into perspective, when I wrote the Harley-Davidson Evolution V-Twin Owner's Bible (Bentley Publishers), my penchant for the virtues of Mobil 1 and other synthetic oils hit the wall. In talking with H-D tech experts and asking whether my Mobil 1 mantra would work in this book, as it did in the Jeep and light truck books, they flatly said, "No!" Why? Because the recommended oil for these air-cooled, arguably Stone Age derivative engines had to have one particular ingredient: zinc. Harley-Davidson's own proprietary label engine oil had more zinc at the time (1997 timeframe) than any other oil available. This oil was "legal" and regulated to a lesser degree because of the lower volume sales of motorcycles. Though zinc was on the EPA radar screen then, total elimination of zinc from all motor oils only came recently. So, this takes us to your current dilemma. To be blunt, zinc additive or your camshaft manufacturer's recommended additive package must be added to the crankcase of any engine that is breaking-in a flat tappet camshaft...Some say that you should continue to run a zinc additive or zinc content motor oil even after break-in. For those unfamiliar with break-in, the most crucial break-in consideration in an engine is the camshaft lobes to its lifters, rocker arms or followers. It takes real negligence to keep piston rings from seating, something like pressing the engine repeatedly to redline with few miles on the odometer. (This causes cylinder walls and piston rings to glaze before the rings can seat.) As you might guess by now, it takes only one good engine dynamometer run to ruin a flat tappet camshaft and set of lifters if not properly broken-in—which includes the use of proper oil additives. There have been several breakthroughs in oil development in recent years. While I once swore by the virtues of more costly synthetic oils, I now find myself at Costco buying cases of Chevron Supreme motor oil with Iso-Syn formulation. Our Jeep 4.0L inline six, which happens to have a flat tappet hydraulic camshaft as OEM equipment, thrives on this oil. Why? Because the key difference between a synthetic oil and a petroleum oil used to be the high volatility molecules found in traditional petroleum based oil. Iso-Syn formulation is a petroleum oil with lower volatility molecules throughout, and this means it behaves like a synthetic oil. Certainly good enough for a 150,000 mile gasoline engine in a vehicle we purchased used at 94,000 miles with a history of running who knows what oil. The additive packages in Iso-Syn Chevron products are ample. This engine gets adequate protection at 1/3 the cost of a quality synthetic oil. This same Iso-Syn formulation oil is available in the LE ("Low Emissions") Delo 400. I began my relationship with diesels and Delo 400 in the mid-'seventies as a heavy equipment operator, working out of Local 3, Operating Engineers. On a road job, the I-80 bypass of Winnemucca, Nevada that moved 1.6M yards of earth fill and realigned a section of the Humboldt River, S.J. Groves from Minneapolis had the contract. They brought a wide range of Caterpillar equipment to the job. I worked a combined swing-graveyard (10-hour) shift from September until the job shut down in mid-December. (An 8 below zero front with a 30 mph wind froze the wetted fill before compaction.) Over those months, I saw boxcar loads of Chevron lubricants and anti-freeze pulled onto the Winnemucca siding. Prominent in this extreme weather (same cold as the Alaska pipeline job without the benefit of closed cabs or reverse fans on the engines) was the exclusive use of Delo motor oil. Your penchant for Shell's Rotella has a basis, too. This is a great oil, just ask any over-the-road trucker. Prior to the recent, draconian measure to eliminate zinc from engine oils, each of these two diesel oils were all you needed to know. Now, especially with a fresh camshaft and lifters, you need to get a zinc additive for breaking in that flat tappet camshaft and lifters! Note: Roller lifters would eliminate much of this concern, and presumably the EPA must presume that most current engines have roller lifters or equivalent. A roller lifter or roller camshaft follower, unlike a flat tappet with its necessary convex base, will distribute the load across the lifter and reduce friction with the roller bearing. When I installed the new Stage 1 Hot Cams camshaft in the Honda XR650R motorcycle engine, despite the wide rocker arm contact surface at the camshaft (more like a roller's width), I raced off to find a suitable "break-in" additive for the camshaft. I added Lucas Break-in Engine Oil Additive with Zinc-Plus™. This additive remains in an automotive engine for 1,000 miles—more like 250-500 miles in an enduro motorcycle engine. If you're big on draining oil shortly after rebuilding an engine, you would need to reuse this additive until the 1,000 miles accrues. I like to change the oil filter right after the initial engine warm-up following a rebuild. This requires top-off of the oil. Add a proportionate amount of zinc oil additive. Moral of the story: Do not run that fresh camshaft and lifters without a zinc additive during break-in! After that, Rotella would work just fine, in fact it is rumored that Rotella has a better additive package than most diesel oils. Chevron Delo 400 and Shell Rotella are good products. Texaco Ursa had a large following, though I'm not sure if Ursa is still readily available. Mobil Delvac is another quality brand. Notice that I'm not suggesting synthetic oils, though many still swear by them. Before the first oil change on our Dodge Ram 3500, the Cummins 5.9L engine had established its permanent oil color: black. Synthetic oil in a diesel is a questionable investment. As for viscosity and climates, the latest crop of "winter" oils from each of these major commercial oil producers has my attention. I've been running 15W-40 Delo 400 year round, and the engine uses negligible if any oil. (The most that's ever been consumed was 1/2-quart in a 5,000 mile change cycle that included towing an 8,000# trailer up I-8's long 6% grades from San Diego to Anza-Borrego and back.) The engine does not leak, a major tribute to late seals at the crankshaft and timing cover. Oil pressure has always been respectable and remains the same today as when the Ram 3500 left the dealership lot over 140K miles ago. I have recently considered changing to 5W-40 Delo 400 or equivalent diesel recommended oil for winter protection, running it year round. That would eliminate cranking stresses on start-up when the truck parks away from its block heater for lengths of time in the winter. Since this is a synthetic base formulation, I may have to eat my words and plunge into the synthetic world of commercial diesel oils. Cha-ching! Here's the link to Delo oil products. Note that Texaco's "Ursa" label is in the listed oil offerings: http://www.deloperformance.com/products/engine-oils.aspx As for your short drives with a diesel, you said it, this is torture. My office is around two miles from the I-80 onramps. In the winter, when below 45 degrees F, if I'm headed to Reno on a cold day, I can be three miles down the interstate before the engine reaches full operating temperature...and that's with the block heater plugged in the night before! I rely on the additional 27 miles of interstate cruise to disperse the cold start/warm-up diesel fuel particulates in the crankcase. Note: We get plenty of sub-freezing weather in the winter, and I always use the factory block heater before a planned trip, allowing 12 hours or so of coolant warming before start-up. I installed a block heater on the 4.0L Jeep Cherokee gasoline engine and use that heater every night, as this is our daily driver. A block heater is a must for any diesel vehicle parked outside. 45 degrees F is my magic temperature for plugging-in the block heater before a run. With a switch to 5W-40 oil, I might change the block heater plug-in to freezing temperatures—or maybe keep with the 45 degrees F practice. The heater works nicely with the block warmed first! On another note, I also use a battery maintenance device nightly in the winter. The Battery Tender or a CTEK charger work fine for this purpose. The CTEK has many additional features. The Battery Tender has kept the OEM Mopar batteries in good condition since we purchased the Ram 3500 new, and that was 10 years ago! I attribute this to the battery maintenance device, which stays on when the truck parks in the winter or in the summer if the vehicle will set for some time. Do the zinc oil additive during the current camshaft and lifter break-in. After that, your choice of engine oil is up for grabs. My preference as an equipment operator "hand" is still the mainstay commercial/fleet diesel oils that carry the off-highway construction equipment and 18-wheeler truck engines over their extreme lifespans. Trust this helps... Moses

Hi, Seb! The injectors on these engines are electronic assemblies, and the 2004.5-2007 system is a common rail EFI. They seem to present less trouble than the earlier Cummins injectors, so parts receipts here should be enough proof. If purchased new, these injectors can be quite expensive! Tire wise, I lean toward the new BFGoodrich KO2 All-Terrain that we tested at Baja in September. This is a breakthrough tire with extended wear capability, the "snowflake" rating and a very strong sidewall wrap with advanced tread and sidewall rubber compounds. The KO2 tire has been tested by the media at Canada, look for reviews from a few months ago. The least hassle will be the OEM size tires, there will not be a speedometer error, and the tires will match the gearing. My very best fuel efficiency with our Ram 3500 was with the stock size OEM tires (happened to be BFGs) that did not alter the gearing or, more specifically, the tire revolutions per mile. Load Range E is a must for whichever tire you choose. As for noises, the very nature of a diesel engine makes it difficult to hear engine "knocks"—the compression piston rattle is a continuous knock! If you suspect engine bearing noises, the best test is the drain oil analysis, capturing the drain oil properly for the test. Watch the engine oil pressure. I expect over 40 psi within seconds of startup cold. Idle oil pressure will drop when the engine warms. Don't compare Cummins oil pressure with a gasoline engine, especially an AMC/Jeep design inline six! What you want with oil pressure is consistency once warmed. The pressure should hold at whatever is "normal" for idle and road speeds. Here are the factory recommended oil pressure specifications for this 5.9L Cummins engine. These are minimum pressures. Again, I like to see over 40 psi at 2,500 rpm and at least 20 psi at idle. The minimum pressures listed are low in my view: Engine Oil Pressure (MIN) At Idle 68.9 kPa (10 psi) At 2500 rpm 206.9 kPa (30 psi) The rest of your testing on this truck is straightforward. Check for clutch slip, "chatter" or roughness on take-off. Listen for gear noise in any gear(s) of the manual transmission. Check for driveline "clunk" or axle ring-and-pinion backlash noise. Listen for axle bearing noise or gear whine under acceleration, "coast" and deceleration. Stock axle gears like 3.73 or 4.10 should be quiet when compared to 4.56 or 4.88 aftermarket gears. Note the brake response for true, straight stopping from higher speeds. Check the steering return-to-center after corners and for excessive steering pull left or right. When checking for steering pull or drift, be objective; try for a flat road surface, not a dramatically tilted or cambered road. Check that all options and accessories work. Ideally, factory installed equipment is best, as there is less fear of wiring issues or poor connections, which often get hidden behind the dash or worse. If aftermarket equipment is in place, check for proper installation and function. The truck should accelerate well from idle to 2,500 rpm. Beyond that speed, the 5.9L Cummins is just spinning itself out, although horsepower continues to climb and should feel strong at 3,000 rpm. "Redlining" (3,400 rpm in this case) these engines is pointless, though some do this when they have no idea how to drive a diesel. You have a whopping six manual speeds with the NV5600 transmission. Whether testing the truck or driving it as an owner, use the gears! For maximum fuel efficiency from a stock Dodge Ram 3500 5.9L H.O. Cummins engine and an unloaded truck, I would be upshifting the manual transmission at 1450-1600 rpm. Loaded, I would strive for 1,600-1,900 rpm shift points whenever possible. Grades, passing and so forth, the stock H.O. will pull strongly past 1,900 rpm, you could spin the engine at 2,400 rpm or higher when necessary or for safety sake. Moses