Tremec 5-speed Transmission Swap for 1971 C-10 Pickup

[Mr Rex]

Does anyone have experience replacing a Muncie SM465 transmission with a Tremec 5-speed in a 1971 C-10? 

Currently my truck has a 3.08 rear differential that I took out of a C-10 with an automatic transmission, which gives me the highway legs that I like but doesn't do so well around town or on dirt roads.    I would like to have a wider range of gear selections than what the Muncie offers, which is why I am considering the Tremec.   But it is pricey.   Any thoughts on alternatives?

[Moses Ludel]

Mr Rex...I'm partial to the SM465 for its ruggedness and compound first gear, though 1st is unsynchronized, which means no downshifting while moving!  The other dilemma is no overdrive. 

With your tall 3.08 gears, the 5th gear in the Tremec would be really tall.  You likely could get by with the SM465 and 31" or larger diameter tires although compound low is not suited for rolling downshifts.  Your C-10 is two-wheel drive, right?  Will 31" tires even work?  If this is a "street truck", custom or lowered, the tire diameter will be limited.

If you want or need overdrive, the Tremec could be practical.  How much horsepower are you producing?  If you want the widest range of gearing plus ruggedness, there's the iron NV4500 five-speed truck box, and a version was used in GM trucks.  I have worked with the NV4500, it's a true truck workhorse with synchromesh on all forward gears.  You typically start off in second (like the SM465) or use first for real loads.  The NV4500 has overdrive.

One of my favorite trucks was our '73 K10 4x4 SWB that had the 350 V-8 and SM465 with 3.08 gears.  Tires were 33" diameter.  The truck had a wide range of power and was highly versatile.  We wish we'd kept that one!

Moses

[Mr Rex]

Moses;

Thanks for the reply.  I agree with the impracticality of trying to use an overdrive while running a 3.08 differential ratio.   Originally, I had a 3.73 rear differential and a three-speed manual transmission in the truck.   The low rear end did well around town but made that little 250 six-cylinder howl whenever I exceeded 60 miles an hour.   I had hoped the Muncie 4-speed with its low first gear would compensate for the loss of power at low speeds while I ran the 3.08 differential, but it was too low for regular use and effectively I still had a 3-speed.   It's certainly a rugged transmission, I pulled it out of a 1969 C-10 4X4 and it's never been rebuilt.  But, as you noted, in addition to first gear being too low, it also requires a complete stop before shifting into that gear.   

Yesterday I ordered a Yukon locking differential and new 3.73 ring and pinion for rebuilding the rear axle.  I realize this brings back the highway speed howling, which is why I asked the question earlier in this thread regarding a Tremec 5-speed transmission.   However, it occurs to me that I may also need a new engine as well as a new transmission at some point in the future.   I have already rebuilt the engine twice which has left me with .060" oversized cylinders, a .020' undersized crankshaft, and at least .050" off the head.  So, perhaps a newer engine with an NV 4500 transmission will be the next upgrade.   

Its been a good truck for forty years, even though I am not sure how much of the original truck remains.  Its not a toy or a trailer queen, I want to keep working it and  maintaining it until I get too old to drive.  My daughter plans on burying me in it, or at least that is what she says, but that seems like a waste of a perfectly good truck, particularly once I install the locking rear differential and a Tremec.  

V/R, Rex

[Moses Ludel]

Mr Rex...Thanks for the insight into the truck.  I am guessing you have a 4WD chassis if a '69 SM465 from a 4x4 bolted in place.  2WD and 4WD transmissions have different outputs and tailhousings...If your truck is a 4x4 ("K-10"), the 3-speed is very rare though on the order list as standard equipment with a 250 six.  You've not mentioned "K-10", so please clarify.

If you have a 4x4, a 2WD Tremec transmission would not mate to the transfer case.  If your Chevy is a 2WD, the 3.73s and Tremec might work with tires up to 30" diameter.  The transmission's overdrive 5th gear could be effective at that rate.  What size tires are you running? 

An NV4500 would be much heavier duty that the 3-speed or Tremec.  The heavy duty version of the NV4500 would be even stouter than the SM465, and that's saying a lot.  Both the SM465 and NV4500 transmissions are suitable for 1-ton capacity trucks and even the lighter end of the medium duty models.  If your truck weighs in the 4,000 pounds curb weight range, the NV4500 overdrive could be useful.  Heavier curb weight than that, an overdrive may be too tall to utilize with the 250 six.

The inline 250 is a wonderful 7-main bearing engine.  I prefer the torque of the 292, which has regained popularity for its "street truck" novelty.  The tall deck 292 has the limitation of fuel consumption.  Despite the displacement and massive torque, a 292 seldom surpasses a 327 or 350 V-8 for fuel efficiency.  A Chevy 305 or 307 V-8 might provide enough power and reasonable fuel economy, too.  I like the 350 with 4-bolt main caps.  During the last few years of the 327 truck engine, the block has a big journal crankshaft like the 350.  We had a late sixties (1968) GMC 4x4 with the 327 big-journal V-8.

Please clarify your truck's chassis (wheelbase and whether it's 2WD or 4WD) and the tire diameter you want to run.  Is fuel efficiency a significant goal?  What are your performance expectations?

Moses

[Mr Rex]

My truck is a long-wheel base, 2-wheel drive C-10.  It started out its life serving as an errand and light utility truck for a gas station in Fayetteville, AR and I acquired it with around 70K miles on it.  

Right now, I have P235/75R15 Wranglers mounted on all four wheels, and probably would like to keep it that way.   Given the cost of gasoline these days, I would like to maintain a relatively high level of fuel efficiency.  At one time I could squeeze 19 mpg out it, but that was a long time ago.

I may be mistaken regarding the source of the Muncie SM 465, since it was about 26-27 years ago when swapped out the original transmission and the cab to accommodate the Muncie compared to the smaller three-speed box.  

Can you recommend a manual or guide for overhauling the differential in that model truck?

[Moses Ludel]

Mr Rex...I have the visual on the truck.  It was originally a utility model with a lot of versatility.  You have had many years of service from your C-10 and will get far more!

I'm all about fuel efficiency these days, as we all should be.  For maximum fuel efficiency, the 3.73s or even 4.10s would work with the Tremec 5-speed.  I support that idea with fuel efficiency in mind.  Which Tremec are you considering?  What ratios?

Even without overdrive, 3.73s would be good for pulling power, which the truck had when new.  If sold, the SM465 should fetch enough to get the ring-and-pinion gear set and bearings that you want.  This is a common axle.  A used Motors professional manual from the period would work.  A used print copy of the factory workshop manual would be even better.  Try eBay.  There are now a variety of reprint books and CDs available, this is one reprint example:

https://www.themotorbookstore.com/1971-chevrolet-truck-chassis-service-manual.html

I like the CD versions for easier navigation and no smudge prints.  If you have a PC or laptop at your shop, that works.  You can also print pages from the manual and take the printed pages into your shop.

I think you would be happy with a 307 V-8.  This would be a compromise between the 250 inline six and a 350 V-8.  The 307 is a "stroked" 283 that produces strong torque and is fuel efficient.  (The 305 is in this niche, too.)  I'd target 8.5:1 to 8.7:1 compression with a mild camshaft and two-barrel manifold/carburetor.

Moses

[Mr Rex]

Thanks, Moses.

i am considering a Tremec 5-speed GM TKX transmission rated for 600 ft-lb torque, max RPM 8000, max shift RPM 7500, 31 spline output, 26 spline input, with gear ratios of 2.87, 1.89, 1.28, 1.00, 0.68, respectively.

This seems a little bit like overkill for my intended application, but I haven't really found a better alternative.   I imagine that it will require installing a frame crossmember, even though the Muncie installation doesn't have one.  I do like the idea of a 307 V-8 as a potential engine swap.

V/R, Rex

[Moses Ludel]

Mr Rex...I like this transmission for your intended use.  Plenty of stamina and the ratios match up well with your C-10's weight and cargo capacity.  A quick search has your original 3-speed's 1st gear at 2.85:1 ratio, so this Tremec transmission would be a good match for standing start torque.  If you do update with a 307 V-8, this would also be optimal ratios for that engine.

The 307 V-8 strikes me as a smart bump in both torque and horsepower.  Here's a link to a useful, downloadable PDF on your 1971 Chevrolet C-10 truck specifications:  https://www.gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Chevrolet-Trucks/1971-Chevrolet-Truck.pdf

On page 6 of the PDF, you will find a comparison between the 250 six and base 307 V-8.  You would gain 55 gross horsepower and 70 lb-ft of gross torque.  The distinction is the rpm for each.  The 250, typical of inline sixes, peaks torque at a low 1,600 rpm.  The 307 reaches peak torque at 2400 rpm.  An actual torque curve chart might show the 307 matching or nearly matching the 250's torque by 1600 rpm, which would be ideal and the best of both worlds.  You can also This would be a conservative "factory" engine swap for your model year truck.  GM engineering knew the consumer needs and the truck's requirements.

The price of the Tremec is staggering, frankly.  Yes, it's a fantastic transmission with a high torque and rpm rating, purpose built for high performance applications.  As a suggestion, though, I would consider a 1966-up Saginaw 3-speed with factory overdrive.  These transmissions use an all-synchromesh front end similar to your 3-speed with a classic B.W.-type overdrive unit.  This was the end of the traditional overdrive era, and you'd need to find one of these somewhat rarer units.  I have rebuild many B.W. transmissions with the R10 and R11 overdrives.  If you're okay with a classic overdrive for use on the highway (coasting in overdrive is a "neutral" sensation, these are planetary units), this would be much less costly.  Here's an example of what I'm describing:  

You'd be giving up the Tremec 5-speed's close ratios (essentially a close-ratio four speed plus overdrive) but gaining an overdrive if that were the objective.  All with factory parts.  These Saginaw overdrive transmissions were available in light trucks and passenger cars and would be a familiar, bolt-in arrangement.  You might need to alter driveshaft length.  Maybe not.

If a synchromesh four-speed is desirable, some adapt the classic overdrive to the popular factory four-speed transmissions.  Here is an example that provides four forward speeds plus the 30% B.W. overdrive ratio:  https://www.motortrend.com/how-to/get-gone-grassroots-overdrive/.  This might be an alternative and far less costly than the Tremec.  There are many photos available at the article.

Moses

[Mr Rex]

Finally finished the rear axle overhaul.   Definitely runs quieter without all the slop and backlash in the gears that had accumulated from 250K miles of hard driving.  With the 3.73 gears it has significantly more zip than with the 3.08 setup.  

Torquing the pinion nut to sufficiently collapse the spacer about gave me a hernia.   I must have applied 300 ft-lbs of torque on the pinion nut before achieving the 18 in-lbs of pinion bearing drag specified in the Yukon directions.   It appears the collapsible spacer that Yukon offers with their locking differential case is significantly stiffer than the stock spacer.  

Someday I would like to understand the design concept behind using a collapsible spacer instead of just relying upon the differential housing to maintain the pinion bearing preload.  

[Moses Ludel]

Good job, Mr Rex!  The collapsible spacer ("crush sleeve") is a means for quickly attaining the right preload without repeatedly changing shims to get the right preload.  It's an initial (factory) time saver rather than any gain in design.  GM axles went to the crush sleeve.  Spicer maintained the traditional shimming method for years.  More recently, Spicer/Dana adopted the crush sleeve. 

When I do shim type axle work, I use a set of "dummy bearings" modified to slide with finger pressure onto and off the pinion shaft.  If the installer is fortunate enough and the axle has never been serviced, the original Dana/Spicer pinion head markings provide a reliable gauge for determining the shim stack height for the new (marked) pinion gear.  (See my article at https://4wdmechanix.com/moses-ludels-4wd-mechanix-magazine-moses-ludel-rebuilds-the-jeep-yj-wrangler-dana-30-front-axle/.)  I trial check the pinion depth (ring-and-pinion mesh/centerline) by temporarily installing the carrier/ring gear and doing a pinion depth tooth contact pattern with the inner shim stack in place.

Once the inner bearing shim stack is correct, I press a new inner pinion bearing onto the pinion shaft with the shims in place.  With the carrier/ring gear removed, I use the outer trial bearing and shims to set the pinion bearing preload.  Once I have the right bearing preload shim stack, I can pull the new outer bearing into position on the pinion shaft and confirm the preload with the pinion nut secured to torque specification.  I then install the carrier/ring gear and verify the combined carrier and pinion preload total.  A tooth contact pattern test while setting the ring-and-pinion backlash completes the process.

There are "tool" versions of my dummy bearings for shops that do a lot of axle work on Spicer and other shim-type axles.  I use take-off bearings in top condition/tolerance for making my tools, sanding out the inner bearing race evenly with a sanding drum in my drill press, carefully removing just enough material to allow finger pressing the bearing onto the pinion shaft.

The crush sleeve has two purposes:  1) set the preload to specification, and 2) provide resistance to keep the pinion nut tight.  The main concern with the crush sleeve is to tighten ever so slowly and not collapse the spacer too much.  If the preload becomes too tight (in-lb setting), a new crush sleeve must be installed.  The builder cannot simply back off the nut to loosen the setting.  For safety, the crush sleeve must continually apply pressure to the backside of the pinion nut;  otherwise the pinion nut can back itself loose even with threadlocker on the threads.  If the sleeve is over-crushed with the nut backed off, there isn't enough force against the pinion nut. 

Yukon likely makes the crush sleeve stouter because most installers use an air gun.  Air guns now put out over 400 ft-lbs torque.  A softer crush sleeve will collapse too quickly and over-tighten the setting.  The higher resistance helps offset air gun torque and the risk of ruining a new crush sleeve.

Moses   

[Mr Rex]

I had to pull the transmission out of the truck this Spring after it began to howl in all the gears but 4th.   I figured the bearings were shot, and I could fix it by replacing the bearings, bushings, and synchronizers.   I must have watched twelve hours of videos on YouTube to get a sense of what was involved in the overhaul before I dropped the transmission, but eventually, I managed to extract it from the truck. 

That is when I realized that I had a 1958 SM420 transmission in there instead of the SM465 that I thought I had.  Not only is the transmission twenty-three years older than the truck, but it is also older than I am.  I'm not quite sure how I ended up with an SM420, because I thought it was taken from a 1970 GMC 3/4 ton when I bought it.  But I suppose I can't complain, that transmission has worked for the past thirty-five years without much attention except to change the gear oil.

When I opened the top cover, I realized that it was the gear teeth that were making the noise; they definitely display signs of wear.   So rather than try to rebuild a 70-year-old transmission, I bit the bullet and ordered a T-5z transmission from Modern Drive Line, Caldwell, ID. 

Would there be any interest in a used SM420 transmission in this forum? 

[Moses Ludel]

MrRex...I'm looking forward to hearing more about the Tremec 5-speed.  What's the torque rating?  Is this the T-5 rated 300 lb-ft torque?  Or heavier duty?

As for the SM420, it is a classic (1947 to early 1968 GM trucks).  The market would be restorers of vintage 1955 Second Series through mid-sixties 2WD GM light trucks.  It does not have the E-brake for a medium duty truck.  It won't work with a torque tube rear axle (1/2-ton 1947 through 1st Series 1955).  If it needs gears, that's a cost issue.

The SM420 transmission was once the go-to for vintage Jeep V8 swaps using a Chevrolet or other GM engines.  (The SM465 has become the updated choice due to availability.)  The more common SM420 has a 7.05:1 compound 1st gear ratio for exceptional reduction.  2nd through 4th gears are synchromesh with a relatively low 2nd gear ratio for normal startups...The mate-up would be easy to a Chevy V8, V6 (4.3L) or a Buick engine with a stock Buick/GM bellhousing.  Advance Adapters has the mate-up to the Spicer Model 18 or 20 and the Dana 300 transfer cases.  Any Members or Guests interested in a "rebuildable core"?

Using the information I provided regarding applications, consider running an ad at Craigslist.  Shipping is costly, so a local Craigslist buyer would be practical. 

Moses

[Mr Rex]

According to the information that Modern Drive Line posts on its webpage; 

1352-0251 TREMEC T-5 WC Z-Spec 5-speed transmission with  gear ratios 2.95,  1.94,  1.34,  1.0,  0.63

10 spline input, 28 spline output shafts

Torque rated 330+ft/lbs

World Class with Cobra pocketed input bearing

Carbon fiber 1-4 synchro Rings

7-tooth speedometer gear drive

To be honest, I am not sure what “Cobra pocket input bearing” truly means, but I suppose I will find out once the package arrives.

[Moses Ludel]

I like it, Mr Rex!  The WC was an eighties era bump that the Mustang GT and H.O. models got.  This should work well for your application. 

Jeep CJs used the standard T-5.  Advance Adapters would upgrade that transmission with a new T-5 World Class.  The C-10 pickup will be greatly enhanced by the overdrive.  You can expect a gain in fuel efficiency with the correct axle gearing.

Moses