The Stovebolt Site Forums The Shop Area Engine Shop Rear-End Swap?

I have a 54 GMC 1/2-ton truck and I believe it has the original 4.11:1 rear-end ratio with 6-lug pattern. My question is I found a 1957 Chevy car rear-end w/ a 3.55:1 ratio and 5 lug pattern. I was told it measures 54.5" from flange to flange and has the following numbers cast into it: CE217, 3726899, GM23. Will this rear-end work in my truck and can I switch axles, so I can retain my 6-lug bolt pattern? Thanks.

Jim

You can usually have custom axles made for your application. For example, if you have a Chevy that you're putting a Ford 9 inch in, you can get axles made with the Chevy bolt pattern for that rear end.

What you want to do is to contact some place that deals with differentials and ask them about your specific application, and see if they can make axles for the older applications. That is an excellent question.

I wish I had a 4.11 or taller rear end in my 3/4 ton. I have a 4.56, so it's only got about a 60 mph comfortable cruising speed and about a 72 mph top speed.

You may be able to have the 5 lug, re-drilled to 6. If something happens down the road you will always have to have one drilled. But the amount of time and cost might be better spent finding a 10 or 12 bolt chevy rear end from the 70's. The 12 bolt I found from a 77 burb has 2-3/4'' wide HD brakes, a BIG difference. The e~brake cables are a near match in length (for my 3100). We moved the axle back 2 to 2-1/2'' rather than the 'kit' has @ 1-1/2'' from chevy duty. I had to make an adapter to fit the end of the E~cable outer housing to the 3100's stock cable adbutment holder.

Jim, What kind of ratio do the '70 Chevy rear-ends have in them? How much modification is needed to make one of these rear-ends work on my 54 1/2-ton GMC? Would I have to modify my drive shaft as well?

Jim

Pretty typical Chevy ratios are:
3.08, 3.23, 3.36, 3.55, 3.73, 3.90, 4.11, 4.56, 5.10. But there may be some variation on that.

You can get these narrow 5 to 6 lug adapters. you can find them cheaper, but this site has good pics and it was the first one that came up on my google search

http://www.adaptitusa.com/index.asp?PageAction=VIEWCATS&Category=7

If you are going to keep the front drum brakes you can change to 54 chevy pass hubs and drums. Then use the 57 pass rear axle and every thing will match. Or go with a Blazer rear axle with 6 lug pattern. To keep stock wheels.

If I do go for a Blazer (Year?) rear axle, what will I have to do to adapt it to my 54 GMC 1/2-ton truck? Drive shaft change, emergency brake cables? Thanks.

Jim

Cujo8,

The 54 rear axle for my Chevy is 62 1/4 inches flange to flange and the ratio is 3.9 to one. I am not sure if the GMCs are the same - probably. Your 57 pass rear end width sounds like it is too narrow. You might think about changing the gear set to a 3.55 to one, that is if you want to keep the stock closed drive shaft.

Others here have done the Blazer swap so they would know more. Find an early Blazer with the ratio you want, order a spring mounting kit from one of the venders. "No Limit" www.nolimit.net has the offset axle mount kit for $103. that relocates the axle to the center of the wheel well. I am not pushing their products, because I have not used them, but the kid across the street from me works there and he just gave me a new catalog yesterday. Nice catalog. Get the Blazer drive shaft with the rear end, it is probably too short but you can salvage the ends. Find a good drive shaft builder. Someone else will no doubt direct you on the brake cables.

If you have a closed drive line now, you will have to change the trans to an open drive line, which is probably why you want to change the rear end.

Get dirty, bust some knuckles, and have fun.

The only part of my drive train that is original is my Rear Axle (Maybe). My 54 GMC 100 has a Chevy 261, SM420 4-spd, and a 3/4-ton drive shaft setup, which starts out as a closed shaft and then becomes open before the carrier bearing. I am thinking that a rear-end swap will be alot cheaper than rebuilding my existing rear-end w/ new gears.

79-84 toyota rear axle is the right width with the same 6 lug pattern. Gears are cheap and readily available from 3.23 and up. But you need to watch out, they are usually 4.10s if the truck had a 4 cylinder.

HR gave you the ratios.
I would go to a site and figure out what rear ratio you want, you might as well do this sort of thing once and you're done
http://www.smokemup.com/auto_math/mph_range2.php
can do this for you. you input the tranny and 'pick' a ratio. I live in the foothills, so mountains are an issue, I have a 3.40 w/ a T5 speed. Your choices are wide if you need to change the gearing on 10 and 12 bolt chevy rears, mine came from a 77 chevy suburban 4x4. For towing the lower (4:10), or speeding on freeways (2:90) to 1 is a benchmark. I had to cut all hangers off the axle and weld on a conversion kit from chevy duty, which moves the axle 1.5''. We actually moved the axle 2.5'' so my 16 gal under bed tank would fit. You can use the ebrake cables that come w/ the 10/12 bolt w/ little mod.
I also believe the rear swap will be BETTER than rebuilding you old rear end and re-gearing.

we had to cut the old hangers off completely so the new kit could be welded on to fit our 51. the kit allows you to move the axle back to 'center' it in the tire well by 1 1/2'', WE DID 2 1/2'' using another 1/4'' plate and redrilled the index hole. It looks great.

Jim, That site you gave requires a subsciption to use the calculator. What is purpose of the Tire Diameter 2 and GearRatio 2? Under transmission selection they list a Muncie Wide Ratio and a Muncie Close Ratio as the only Muncie choices. I have a Muncie SM420 4-speed tranny, which choice would be correct if any?

Jim

I believe it allows you to view 2 at one time.
It didn't used to cost but now it does, too bad.
if you do a search on rpm vs speed vs ratio. my link shows gearing w/ a T5. Tire dia counts because it changes the ratio, taller dia means faster speed.

I want to start searching for a used chevy rear-end for my 54 GMC and I need to know what measurements I need to have and exactly where to measure. Do you measure from the out side edge drum to drum or from outside axle flange to flange? Are there any other measurements I need? Are there specific year axles I shoud focus on or some I should avoid? Thanks for any help.

Jim

Hot Rod Dad, if you search for "Eaton" in the archives you will find all the info you could ever want about installing 4.10 gears in a 3/4-ton truck.

This was a big help for me when I swapped out my gears in my 54 3600 3/4 ton.

http://www.oldgmctrucks.com/page0276.html

Want to know about swapping out a rear end.
and what to use Here's food for thought.... on 50’s chevy’s By: Jim Forbes

The 82-newer Camaros are wider than the older ones, so you should stick with the 70-81 models. The 75-79 Nova uses the same rear as these older Camaros, I believe. The 68-74 Nova chassis is the same as a 67-69 Camaro; the 75-79 Nova chassis is the same as the 70-81 Camaro. The 82-newer Camaros used the small 7.5" rearend design that the 78-newer Malibu/Monte Carlo/regal/cutlass etc used, but it's quite a bit wider. Some of the 82-newer Camaros used different rearends, such as the Dana 44, and some wierd Australian rearend. Of course, if you want to make sure, get out your tape measure and check yourself! I may be wrong.
Here's another one from Jim on the subject---- There are lots of rearends available! Some fit better than others. For 6 lug rearends, the 64-69 1/2 ton 2wd Chevy (and some GMC) trucks have a 12 bolt rear, about 60-61" wide (I measure them where the wheels bolt on). The 70 2wd and 70-81 4wd have a 6 lug 12 bolt that is a couple inches wider, but will fit under a Task Force truck as long as you don't get too wild with wheel/tire width. The 12 bolt truck rearends from the 60s usually had 3.70 gears, which is a bit much for extended highway driving at 75 mph. You can swap the differential carrier and ring/pinion gears from a later TRUCK or VAN 12 bolt, the 70s trucks usually had 3.08 or 3.40 gears. Of course, you'll need to know how to set up ring/pinion gears, bearing preload, and all that other neat stuff to do this. These 60s truck 12 bolt rearends are from coil spring trucks, so the perches are in the wrong place, and they have some extra stuff on the housing for a panhard bar, which you won't need with leaf springs. Most 60s GMC trucks, and some Chevys, had Dana 44 or Dana 60 rearends, and leaf springs. These rearends are 6 lug, about 60" wide, and will bolt into a Task Force truck (with some fudging, the perches are about 1/2" too far apart). The brakes use different parking brake cables, which is a problem, and the drums have a different offset. Gear ratios range from 3.21 to 3.92 normally, the 3.21 is found behind some GMC V-6 engines, and is a nice ratio for an old truck. The Dana 44 uses a standard Chevy 1310 yoke, but the Dana 60 uses a heavy duty yoke, which takes a larger 1350 series ujoint. A similar Dana 40 rearend was availalbe as an option in 59 Chevy trucks, equipped with positraction...rare, and with a 3.92 ratio. I have one of these rearends, it was in my extended cab truck...I'm saving it for when I build a race truck (one of these years).
The 71 and newer 2wd trucks use a 5 lug 5" bolt pattern, same as the 71-76 full size cars. There is not much available in the way of matching front brake rotors that will fit an old truck, so this rearend is not too popular a swap, unless you get the 70-up 4wd 6 lug axles. Chevy also used 10 bolt rearends in lots of cars, in varying widths. A common one is the 61" wide 70s vintage Camaro/Chevelle/Nova (and clones) 8.5" rearend. In Camaros/Novas it has leaf springs, but the perches won't work with old truck springs. In Chevelles, it has coil springs, with lots of extra brackets to cut off, and the cast in mounting "eyes" on top, where the upper control arm bushings fit. Wheel bolt pattern is 4.75", and there are front disk brake kits available to match, or you can use the 53-54 car front hubs/drums on the original 50s truck brakes, to get the same bolt pattern front/rear. This is a good rearend for using in an old truck, the ratios are commonly 2.73-3.36, with higher gears available. The axle shafts are usually worn out in these things, so check them (pull the cover, lockpin, and C clips out to get them loose) where they ride in the wheel bearings...before buying the rearend! The 55-57 Chevy car rearend is almost a bolt in, the perches need to be relocated to the top of the housing though. It has the 4.75" bolt pattern, and ratios are usually 3.55-3.73, but sometimes you'll find a 3.36. The 78-88 mid size GM cars use a 7.5" 10 bolt, which is about 58/5" wide. This rearend would work well in an early (older than 47) truck, but it is quite light duty. Ratios are usually 2.29-3.23, which means you want some torque in the engine to pull it...but rpm will be low. This is a coil spring rearend, with all the mounting brackets that need to be cut off. The Ford 8" and 9" rearends come in a whole bunch of varieties, and only a few are usefull in oletrucks. The late 50s full size cars have a nice one, but it's not easy to find brake hardware, drum, etc anymore. The mid 60s midsize cars, such as the Fairlane, have a rearend that is about the right width, and would be a good candidate...if you can find one. The Maverick/Granada is very narrow, about 56.5", and would not fit anything but a very early truck, or perhaps a tubbed Pro Street truck. The 60s full size Ford car rearends are usually too wide, but if you find one, measure it and see! Most earlier full size, and all mid size, cars use the 4.5" bolt pattern, while later full size cars use the 5" pattern. The Ford trucks have a big 5 on 5.5" pattern, with a big center that takes some work to redrill to anything Chevy. Ratios range from 2.47 to 4.30, and the axles come in 28 or 31 spline varieties. There is lots of interchange possible with the 9" rearend, which is why it's so popular...I have one in my 55 Belair, and in my 57 Suburban chassis. Unfortunately, they are getting expensive, especially when you have to shop around for just the right one that will fit. So...if you don't know if a rearend will fit, or what it came from, get out your tape measure and see for yourself! The most important things are overall width, and wheel bolt pattern...then concern yourself with ratio. I like a 2.75-3.0 ratio for a V-8 powered truck that will spend lots of time on the highway; about 3.2-3.7 for a 6 cylinder or small V-8 for in town and limited highway use, and the stock 3.9-4.56 ratio is great if you have to use your truck to haul lotsa weight, and you don't have much engine...just don't plan on going much faster than 55!