View Full Version : Rear Axle swap

08-10-2015, 10:04 AM
Hello All,

I have a 56 BA, that as far as I know has the original rear end in it. While getting on her pretty good this past weekend, I twisted the drivers side axle in half. I also have an old (56 BA) parts car, so I took the Center Section (Chunk) and axles out of it.....but apparently it has a 57 chevy rear end in it, because the axle bearings are 3.00" OD.

Does anyone know if I can just replace the (57) axle bearing on this replacement axle with the 56 bearing? The lengths look very close....but I can't say for sure due to my OEM being in two pcs. The Center sections look identical and even have the same size ring gears and are the same Ratio.

Gotta get back to work, so may be a delay in my response.

Thanks in advance,

08-16-2015, 07:38 AM
Update & Follow up ? --
Good News...... Yes, it appears the axles themselves are the same (at least in my case they were). Installed new bearings and am in the process of putting things back together.

On a previous post, i had issues with ride "stiffness" so i decided while i have it apart i am going ahead and replacing all the leaf spring bushings.
Now i have a some follow up questions--

What is the correct number of leaf springs?
Also, would like to know what Length should each leaf be?? Mine only has 3 and I'm not sure that's correct.
Does it matter how the shackles are installed? (arch to the rear instead of to front)?? What would this impact?


08-16-2015, 08:20 AM
4 leafs including the main leaf were standard on cars. 5 leafs were optional on cars (think taxi) and standard on wagons. 6 leafs were the heavy duty option on wagons.

On a 4 leaf, the short leaf is about 2' long and the other two are progressively longer. On a 5 leaf, the short leaf is only a 1' or so.

Your rough ride problem could easily be the shackles. The arch of the C shape should be to the front of the car. If it is assembled with it to the rear, the shackle will hit the shackle mount before the spring can move much - and this will give you a really rough ride.

08-16-2015, 06:20 PM
Thanks Rick,

The info is very much appreciated.

08-17-2015, 05:06 AM
Good Morning All,

I'm considering changing the ring and pinion to a 3.08gear and would like to keep the same Carrier & pumkin -- Currently I have a standard open face (non-posi) rear end, with 3.36 gears.

My question is what series pumkin / carrier is this? AND is going to a 3.08 ring & pinion doable with what I have?
I "think" the current ring gear measures 8.5"...does this sound correct?
Do you recommend any specific brand or supplier??

Last, Is there a cheat sheet that will tell me what the casting numbers mean? (11-37 ---8726888 gm 8 02882)


08-17-2015, 05:55 AM
OEM 55-64 is 8.2 ring gear, same diameter as early 10 bolt, 71 and newer 10 bolt is 8.5. 11-37 = 3.3636363636.

08-17-2015, 09:24 AM
Thank You markm

08-18-2015, 05:02 AM
Hello all,

I'm going to put my old 3.36 gear back in it for now (hope to find a complete pumpkin with a 3.08 later on). In the meantime, Is there any reason I should NOT use 85w140 oil in this used unit? I believe 85w90 is recommended....but I would think thicker oil would help keep this used unit quieter.

your thoughts?


08-18-2015, 06:59 AM
I only use Chevron Delo 80W90 because with GM Posi additive my rear ends are very quiet. I have convinced others with noise to follow suit, especially on lockers which is about all I own.

08-18-2015, 09:30 AM
Thank You for the feedback markm,

I'll give it a try.

08-22-2015, 06:43 AM
Update & Follow up ? --
Good News...... Yes, it appears the axles themselves are the same (at least in my case they were).

Correction to post #2--
I got ahead of myself with that post. NO the axles are NOT the same. Apparently in the case of my "old junkyard parts car" the rear end turned out to be a mixed bag of crap someone threw together 25 years ago. I don't know what they tried to do or were thinking, just that it's now a mixed bag. Sorry Guys ---- I will NOT knowingly post false information.

Now for an update: I have since found the correct axle ($40.00), installed new bearings, installed 3rd member, new U-joints, new rear Urethane bushings & added missing lower leaf spring. The bushings were shot and shackle was backwards, with both of those corrected she now "sets" completely different. If all the above works good, then my next step will be to get the back end raised back up a tad. With only 3 leafs she looked like a low riders (which is NOT my thing). Hope to give her a test drive later this weekend and then adjust from there.

Question: While the 3rd member was on the bench, I secured the pinion so it would not move, and checked the backlash. It was at 0.012" -- which i think is good for a used unit. HOWEVER, after i installed the drive shaft...... i noticed that the slack @ drive shaft seems to turn about 0.125". Is this normal?


08-22-2015, 12:05 PM
I think you're ok on the slack.

Seems you've fixed a bunch of things that will have positive results.

08-23-2015, 06:19 PM
Just got back from a 60 mile test run and all i can say is "WOW". She rides 110% better, so much smoother than before. Now she sits lower in the rear than before and I may want to raise the back end just a tad at some point.....but not gonna stress over that right now. Perhaps it will grow on me the way it is.

Next project will be brake related, then maybe that 3.08 gear.

THANK YOU to all who added input / info.