The Stovebolt Site Forums The Shop Area Driveline Rear end swap candidates

Hoping you guys could save me hours of research and staring at a computer screen.

What rear ends have you guys swapped into the '36-'38 trucks? I'm keeping the stock wheels so wondering if there's a good candidate that is the correct width that's already a 6 lug axle.

I saw in another post Colorados and Canyons being mentioned, but the pinion offset was brought into question. I was originally planning a Ford 9" but I'd need to buy custom axles. Before I spend money on that I thought I'd just look to see if there are other Chevy or foreign options that are already 6 lug.

Ron

Help the guys out with a little more information.

What is the goal of your truck build? Daily driver better gearing, resto mod, stock build etc.

'36 Low cab, 235 swap with S-10 T5. Just looking for more/better drivability for summertime cruising. The ultimate goal is to safely do 60mph but maintain stock look.

I found a 69 C10. 3:08 6 lug rear on. CL for a good price. The rear had been installed in a 58 1/2 ton. 69 saddles had been cut off & leaf spring saddles welded on. I reversed that work & installed in my 66 C10. All C10 s have 12 bolt rears , pinion is slightly different than the car 12 bolts. I also retro fitted a posi unit. Truck has several hundred miles on it now & all seems to be working well. Seems to me you need to figure out the width you can live with & go from there

There are quite a few options, but if you already have a T5 with OD….I’m not certain you really need different gears to cruise at 60 mph. Do you know what ratio you have now and what OD ratio you have? Tire diameter would be good to know as well.

I am not conversant in the 30s trucks and what axle width they are. AD pickups need rear ends in the 60 inch range. If your truck is similar…..

Nissan Hardbody pickups are close to right width and right bolt pattern

Nissan Frontier and XTerra are as well. Have to stay earlier side. Somewhere around 2005-6 they get wider.

Late 90s Isuzu rodeos had a 6 lug version of a GM 10 bolt. I’d love to have one as the gear ratios are almost infinite. They are getting scarce.

55-62 Chevy truck rear ends. Most are 3.90, but you can buy a 3.38 Ring and pinion.

63-69 Chevy truck rear ends. 12 bolt GM, and carry a few different ratios. 3.73 is super common.

The truck is stock driveline now. The 235 and T5 are not installed yet. Need the rear end to (eventually) complete the conversion. T5 ratios's are: 1352-145

1985 - 86 S10

3.76

2.18

1.42

1.00

0.72


Edited to include tire OD is 29.02" according to Coker.

I put a GM 10 bolt with 3.73 gears out of a 69 LeMans. had to redo the pads for the leaf springs but the width was good. I have a 39 gmc T-14, 4.3l with a 4l60e.

Ron, Have you measured your existing axle from WMS to WMS (Wheel Mounting Surface)? If you can give us that number, it would make it easier to try and suggest a possible later open drive (but still 6 lug) axle that will fit your 17" Artillery wheels. It will probably help for us to know what the wheel offset is on the 17" wheels as changes to the axle width will affect where your wheel/tire combo sits inside the fenders.

Others with more personal experience on what gears would work best with your 235/T5 combo will probably chime in here soon.

My axle is 59" from WMS to WMS. Spring perches are 41" center-to-center, but I don't expect to find something that already has the proper perches at the proper spacing. Just thought I'd throw that in there in case anyone asks.

As for wheel offset, I'll have to measure. I will say that my tire centerline sits a little to the outside in the fender, so I probably wouldn't want to go much wider on an axle. There's a little wiggle room there but probably not much. Maybe 60" total WMS to WMS width max.

I was considering the same conversion also, but wanting to keep stock rims and appearance. I was considering the Colorado rear end with six lug but read that the axle hub diameter is greater on it, not sure how much things could be modified to make the rims fit properly. I would like use the T5 also. But with wanting to keep it as stock as possible, I am leaning towards swapping the torque tube rear end for a 3.55 gear set.
I thought I read it on here about that six lug on a canyon rear end would have some differences as far as the stud size and axle hub dimension being larger. Can anybody confirm any of this?

Axle hub diameter? You mean greater than the center hole on the wheel so the wheel won't index on it? If that's what you mean, that could probably be turned down.

My best friend has a 36 lowcab with a 235 and T5. It has a 3.90 55-59 rear. His is still in a lot of pieces, so he can't report on any driving issues with body roll vs. the fit of the axle and wheels and tires. That gear ratio combined with your tires and 5th gear would put you at 67-68 mph at 2200 rpm.

He also has a 29 coupe with a 216 and T5. The rear in it is a 55-59 (62?) 3.90 third member swapped into a 39 truck housing with solid perches welded on in the right spot (running the 39 axles). I am wondering if your 36 axle housing would accept the 55-62 third member in the same way, ensuring a good fit, and if the axles would work as well. I haven't had a chance to look in my parts book, and I fully expect to find different part numbers on the axle housings for different reasons even if the centers will swap just fine. Maybe someone well versed in the earlier trucks can chime in on interchangeability.

I put a malibu rear end in my 37 so its 5 lug.....
...but you could have machine shop redrill pattern
...on another note I have a RIM that will fit a 5 or 6 lug axle but cannot remember where i got it. I used it for my spare tire for my 6 lug panel and 5 lug on my 37.
Just a thought.

The '36 is an enclosed torque tube driveline and rear end, so it has to go when the T5 is swapped in. And if I am not mistaken, you cannot even change gear ratios in these old differentials.

5 lugs are a 4.75" (chevy) or 4.5"(Ford) while the 6 lug is 5.5". I don't think there's enough surface area on my 5x4.75" axles to redrill a larger diameter pattern.

Right.

You unbolt the third member and torque tube assembly and remove it all as one big piece from the axle housing, and bolt in an open drive third member from a 55-62 truck in its place, then fab or modify a driveshaft to replace the torque tube. Replace or otherwise immobilize the pivoting spring perches, and you're set. That's what I did on my 50, and that's what my friend did on his 29 using a 39 truck housing, which brings me back to wondering how similar the 36 truck and 39 truck housings are, and if it could be an option for you.

There are/have been 3.38 gears available for them, but in my personal experience, as-is the 3.90 works very well with the tire size, overdrive ratio, and inline 6 power band.

I didn't know any of this would be an option. If I can do this with my 36 housing, it's definitely something I would want to do. Thanks for making me aware of this possible option.

I'll try to figure out if it's possible, but if anyone knows whether or not my housing is compatible with the 55-62 third members, please let me know.

Ron, A quick check of a 1929-46 Chevy Master Parts book shows the 1936 FB rear axle listed as GM# 601925. A one year only axle per my research. It doesn't cross over to any other axle housing that I could find. Doesn't necessarily mean a Task Force open drive differential (third member) won't bolt in, but I would say not likely.

A little snooping through some older threads in Stovebolt came across this conversation much like yours. The last reply by Bolter Pre '68 Dave suggest using a later 1947-50 1/2ton axle mated with the Task force differential to get what you seek.

Others should be along to offer more info and suggestions.

Even if the 55-62 third member doesn’t directly swap into your housing….it would be easy peasy to adapt a complete rear into your truck. They are still very common and usually CHEAP…. if not almost free. So many people take them out for 5 lug swaps and/or hotrod projects. You will get Bendix brakes out of the deal, if you haven’t already upgraded those.

As for gear ratios, I sourced a replacement for my worn-out 55-62 rear and completed the swap recently. I “accidentally” ended up with a 3.38 gear set. Whether they are modern gears or old gears, I do not know.

I was concerned that taking off from a stop or accelerating in 2nd gear (this is an SM420) would be struggle. I have 30.5 inch tires. However, I honestly can’t feel much difference taking off….and highway cruising is more comfortable.

That said, I am also planning a T5 swap (someday) and I figure the 3.38 will make OD kinda useless. But I like it enough so far that I might just step down in tire size if/when I get around to the T5 project.

I saw the 33-63 carrier and cover gaskets are all the same, so it seems the third member will at least bolt in. Question now would be would my axles work?(diameter, spline count, location etc)

Two other issues come to mind (just thinking out loud here)...Could I upgrade the rear brakes to Bendix style on this housing? On the front axles, I think it would just be a matter of drilling the 7/16 holes to 1/2", but I don't know if the rear would also be the same.

Also, availability of new bearings.

Do you happen to know what width those rear ends are?

I don’t have the official answer right in front of me, but it’s somewhere in the 59-60” range.

Close enough.

A cautionary tale:

As much as they are available and affordable, so are the 55-62/55T/HO33 rear ends OLD. They are OLD and who knows what kind of life they lived. A life of ease or a life of constant abuse and neglect. There’s a “pig in a poke” element to these things. Very few sellers of one are going to know much of anything about its history.

I am a cheapskate. My primary motivation for installing this current rear is that I literally got it for FREE, and I figured some spring perches and a couple brake parts were a reasonable gamble if it ended up being a turd. Seems I got lucky. So far, anyway.

Rebuild kits are available but spendy compared to more common rears like 12 bolt GM, 9 inch Ford, etc.

I paid 150.00$ on CL for my 69 C10 6 lug 3:08 . I seem to recall it is 60 “ from backing plate to backing plate.

That 60s 12 lug would have been the first choice for my swap.

Kept an eye out for a while and the ones that were nearby were too much money. The deals were farther than I wanted to travel. This other 55.2 rear end just kinda fell in my lap and I decided to give it a try.

Those 63-69ish C10 6 lug 12 bolts are also OLD. But they carry the advantage of having widely available and affordable replacement parts. And a wide range of gear ratiosz

...fyi, the automatic rearends, up to 62 should be ones with higher ratio if i remember correctly.
I suggest changing out the older one.

In my '38, I used a mid-eighties 4WD S-10 axle (the 4WD axles were wider than the 2WD axles) with 3.42 gears and 4" wide two-piece bolt-on 5 to six lug adapters and stock wheels with original size bias ply tires. It was just the right width.

I used the .72 overdrive T-5 with a stock rebuild 261 inline and was very happy with the pep in the old trucks step.

Do you know the overall width measurement with the adaptors? Seems like that would be too wide, but I guess not. I need to be around 59-60" total width, WMS to WMS.

4" thick each

I meant the total width of the rear including the adaptors.