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Dodge Ram 3500 with 48RE Automatic Transmission Shudders on Take-Off

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#1 Megatron

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Posted 01 July 2013 - 10:18 PM

With my '06 Dodge Ram 3500 4x4 and 48RE transmission (Cummins diesel power), I notice when pulling and away and accelerating from a dead stop, like a stop sign, I will get the slightest vibration in the transmission. I assume it to be the clutch plates on the torque converter but not sure if that is right. it only does it from a dead stop and only through a few 100 rpms. it acts like trying to take off with a heavy load on a standard transmission.

 

I compare this to a solid flywheel conversion we did on an older powerstroke ford. to save a few bucks, we ordered the solid flywheel and clutch kit that didn't have the springs in it (like factory). well that was about the worst thing you could have done to that truck when hauling a heavy load. that thing would buck no matter how you feathered the clutch peddle lol. that action is what my truck feels like taking off, just not as violent and very subtle. no matter the tranny temp or load on the hitch. never less and never more. Any ideas?


If you think its expensive for a professional to do it, wait until you see what it cost for an amateur to do it... 


#2 Moses Ludel

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Posted 01 July 2013 - 11:34 PM

You described your take-off shudder well.  For openers, this is not likely converter related, as the converter clutch is not active at this speed.  If it is the converter, this means the converter clutch is dragging, in which case the symptoms would get steadily worse and cook the converter.  If you do suspect the converter, I can share how to test it in the truck.

 

Some would jump to transmission issues like band adjustment or worn clutch packs, motor mount issues, with the Cummins especially, and surely this could contribute.  Likely you have done the band adjustment during service work, though.  There would also be a benefit to upgrading to the aluminum accumulator piston that I describe and install in my Sonnax survival upgrades.  See that article at: http://www.4wdmechan...nsmissions.html.  You'll see the accumulator piston change there, too.

 

I like your gut comparison to the Ford Powerstroke that lost its clutch and flywheel harmonic dampening with the solid flywheel and clutch install.  You may have a similar harmonic or actual binding issue with the shudder you describe.  This may come as a surprise, but I would look elsewhere for that load shudder when you get the truck moving: check the rear driveline/U-joint angles.  You have a 6-inch lift on the truck, and I'll share some pointers here.

 

Your Mega Cab wheelbase likely uses the two-piece driveshaft.  If so, the shaft from the transfer case to mid-shaft bearing is probably stock still.  Maybe you've dropped the mid-shaft bearing to reduce driveline angle at the rear piece.  In any case, the U-joint angles must "cancel each other", meaning that an angle at the transfer case should have the same cancellation angle at the other end. 

 

A common issue with taller lifts is to not have the joint angles cancel properly.  For example, there may be a straight shaft out of the transfer case and through the mid-shaft bearing.  If so, the angle of the second/rear driveline should have U-joint angles that cancel each other (complementary angles) on the second or rear shaft. 

 

Many think it's great to angle or rotate the rear axle pinion upward to reduce pinion joint angle.  That only works if the angle either 1) matches the angle complement at the other end of the shaft (which is impossible) or 2) the front end of the shaft uses a double-Cardan or CV type joint as seen in the photo below.  Also see this Jeep XJ Cherokee article at the magazine for a single piece driveline and 6-inch long arm lift:

 

As a final note, you have shared that you're still running 3.73 axle gearing with the 37" oversized tires.  This is enough to cause extreme take-off loads and maybe even the shudder you describe.  The 3.73:1 gearing is marginal even with the factory tire diameters of less than 32".  At your current ratios, the gearing is way out of balance.

 

Moses

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#3 Megatron

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Posted 16 July 2013 - 06:17 AM

Thanks for the info, Moses!

 

  You are correct. During the last round of transmission updates we did spec as many things as we could during the build. Since the problem was there before and after, I ruled out some things like band adjustments and the accumulator. My inexperience with the diesel and its automatic transmission configuration is what lead me to suspect the transmission as the origin of the vibration. Call it fear that the 48re has problems lol.

 

  Okay. I took some time this weekend to explore my driveshaft angles and condition. Even though my truck is lifted, it has a matching carrier bearing drop bracket and the wedges for the rear leaf springs to correct rear end housing rotation. Everything looks to be close to correct (without using an accurate degree finder that is. (I have a new gauge on the way). All u-joints feel tight and the carrier bearing and bushing seem solid. However, there does seem to be and excessive amount of play on the pinion shaft going into the rear end. I am researching that currently (looking at your write up on rebuilding the AAM 11.5) so I can get an accurate measurement on play. This is one problem with not owning your truck from day one. You never really know what the last guy did with it.

 

   I have dealt with drive line angle issues in the past (lifted YJ) and I am aware of the need to be accurate with CV's and pinion angles. I spent countless hours testing different angles and joint types trying to overcome way too much lift with a short wheelbase ha-ha. What? Who hasn't wanted a 6" spring lift on top of a spring over kit?? I guess experience isn't learned from success but from failures instead.

 

  I am planning new gears later this summer to match my tire size. So even if I find that my rear is currently out of spec, I doubt I will take much action until it is time to swap them out. So if the problem truly lies within the rear it will be a while before I can confirm it.  

 

   When I get my new degree finder I will make a detailed account of driveline angles. Its hard to spot little variations with an analog style degree finder.  

 

  As always thanks for your replies and input. You should really write a book or two about mechanic work or even a magazine ;)


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#4 Moses Ludel

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Posted 16 July 2013 - 01:21 PM

We each have read or heard enough about the 48RE failures and aftermarket heavy duty replacement parts solutions to be skeptical. Worse yet for me, I tried to discuss the 48RE with a Mopar engineer at Moab.  We were test driving new Ram Power Wagons with the 5/6 speed automatics on Poison Spider Mesa Trail, and I could see his eyes glaze over.  This was a look I've seen many times as a professional, when manufacturers move on from a product and no longer have an interest in talking about "old technology".  He may have thought I was a 2005 Dodge Ram 3500 4x4 collector.  After all, the truck was six model years old!

 

Chrysler's now on to better things, including abandonment of the time-honored A727 transmission architecture with an overdrive thrown into the mix.  I remind myself that we saw the A727 Torqueflite behind 426 hemis in muscle cars, tucked into Class A motorhomes behind the 413 and 440 wedge-head V-8s, and joined to the original 12-valve Cummins in the earliest Cummins-Dodge Ram trucks.  Does the planetary overdrive really make that much difference?  Well, I do have suspicions about plastic accumulator pistons ("weight saving?") and stamped sheet metal looking band struts.

 

The driveline issues are a possibility, the angle gauge will eliminate guesswork.  You should be an expert after dealing with drivelines in a 94-inch wheelbase YJ Wrangler with a spring-over lift plus 6-inch spring lift!  For the record, the steeper a driveline angle (side view) and U-joint angles, the less torque the driveline can handle.  These physics reflect the angle of the U-joints and the torque needed to rotate them on a tilt.  Minimizing and matching driveline angles increases the life of U-joints and the torque capacity of the driveline.  1-1/2 to 2-degrees angle would be the least.  Less than that will not keep the needle bearings rotating.

 

Check out my 11.5" AAM axle rebuild and setup of the 4.56:1 ring and pinion gear set.  You'll find that the ring gear backlash setting is quite close for an axle/ring gear this large.  I did follow that setting with success.  The OEM 3.73 gears (bought the truck new) did have noticeable backlash like you describe.  That is gone now, the pinion backlash feels normal, and there is no "clunk" on forward to reverse gear changes.  It's rather annoying for an axle to have pinion clunk, though it's not necessarily a defect—especially on larger ring-and-pinion gear sets.

 

When you check that rotational play at the driveline, make sure you're not adding the differential gear play into the mix.  Move the shaft lightly to the points of first resistance.  That's the actual pinion shaft backlash.  If you're not hearing a whine on acceleration or coast, there's not likely a wear issue.  Check the axial/side movement of the pinion shaft, too.  As a point of interest, the 11.5" AAM axle is very stout, a proven G.M. design.

 

When you do swap gear sets, you can address the backlash issue.  Inspect the differential gears for play, too.  That's the time to make remedy.  As a footnote, changing the ring-and-pinion gear ratios will take a huge load off your 48RE.  The take-off shudder may diminish or disappear, an indication of torque converter loads.  You now have me paying attention to my truck's take-offs, and there is a moment of torque pull.  This could be the torque converter, it's high on the list of 48RE OEM parts "ready to go at any time"...

 

Write books?  You know what they say, "You're only as good as your last book—or next success!"  I say, after seven books that include best sellers, "Why not quit while you're ahead?"

 

Moses


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#5 Megatron

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Posted 05 April 2014 - 09:07 AM

Well I know its been a while since I kicked up this thread but I would like to post my findings and results.

 

   I took Moses advice and checked the angle of my rear drive shaft through the mid support with a digital level (after my eyes tried to tell me it looked fine lol). I discovered the angles where not as true as my eyes had lead me to believe. The front half of the shaft was at a different angle than the rear half.  So after a few measurements, some shims and two longer bolts... boom no more shudder on take off. I wouldn't have believed a set of 3/8" shims would make a difference but man did it ever. Truck takes off like factory again. Just proof that with an hour of time and some hand tools you can fix something with noticeable results lol.

 

  I guess to look back at it, these trucks make a considerable amount of power/torque and have to get a crazy amount of weight moving at take off. So something like a degree or so of angle can be magnified into a bigger problem. It is also a relief not always thinking that maybe your ring and pinion gear is on the fritz.

 

Thanks again, Moses, for taking time to help those who don't know become those who do know...


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#6 Moses Ludel

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Posted 05 April 2014 - 10:33 AM

Great, Megatron!  Your truck deserves to be free of shudders...

 

When the U-joint angles are different, opposing joint rotational forces work against each other.  Envision the angled arc that each U-joint follows as it rotates.  Since part of the joint "compresses" and the opposite side "expands" during each rotation, there is actually a speed-up and slow down over the arcs.  The driveshaft/joint input and output speeds remain the same; the U-joint design compensates for speed variations during each rotation of the joint.

 

Simply put, if the rear driveshaft's front U-joint angle differs from the rear U-joint angle, even if the two joints align properly in "phase", they have irregular speed-up/slow down patterns over their arcs of travel.  So you get a vibration because the shaft is fighting itself end to end.  Another cause for this vibration is when a splined driveshaft is assembled with the cross-joints misaligned.  This is "out of phase" and a real cause of vibration.  It can even tear apart the driveshaft since the speed-up and slow down over the U-joint arcs of travel run at different cycles.

 

You mention power/torque, and that brings up another concern.  A driveshaft loses torque capacity as the angle/slope of the shaft increases.  When a vehicle gets "lifted", the typical 4x4 scenario, if the driveshaft slope increases, the torque capacity of that driveshaft diminishes.  U-joint life suffers, and failure of joints is often common.  Even when the U-joint angles match as they should (by shimming the pinion angle or mid-shaft bearing properly), the U-joint lifespan is shortened.  This is strictly a function of U-joints: steeper angles make the joint weaker.

 

One way many offset this risk is the use of a CV or double-Cardan joint at the transfer case output yoke and a single Cardan joint at the rear axle pinion yoke.  The CV not only reduces the angle on each joint within the CV assembly, it also helps knock off the driveline slope factor considerably.  Since the double-Cardan CV joint has "self-cancelling" angles between the two cross joints, the rear axle joint angle (a single Cardan cross joint) can be very close to straight when measured at static vehicle height—with axles weighted or on the ground.

 

Actually, 0-degrees of U-joint angle is unacceptable for U-joint survival.  When running a CV driveshaft, I set the rear axle pinion joint (single-Cardan) for 1.5- to 2-degrees angle with the vehicle at static curb height and weighted.  This minor angle allows the joint's needle bearings to rotate in the bearing caps, which prevents them from starving for lube and also distributes the load uniformly over the needle bearing sets within the U-joint caps.

 

Note: The 1.5- to 2.0 degree rear joint angle is achieved by rotating the axle housing to angle the pinion shaft and yoke upward.  There is only one "downside" to doing this:  Lubrication/fill of the differential is thwarted by the dropped fill plug height.  Aftermarket differential covers for lifted trucks often have a relocated fill plug, higher on the cover to permit normal fill levels with the pinion angle rotated. 

 

The amount of rear axle rotation has little affect on chassis geometry or spring action.  Many lift kits provide a tilting spacer block to restore U-joint angles.  On installations that require use of spring-to-perch wedges to restore the rear U-joint angle, I use steel and not aluminum wedges.  Steel will withstand more punishment and not pound out or loosen over time.

 

Thanks for letting us know how this worked out, Megatron!  Great to hear your Ram is back in top form...

 

Moses





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