Technical Pontiac/Olds Rearend TECH...post it here...

That would be a '57 or '58 rearend...as far as swapping into a 55 chev, I believe it's a direct bolt-in swap except maybe for u-joints or driveshaft length...oh, and your rearend has a 5x5 lug pattern instead of the Chevy 4.75x5

 

hey this thread has been pretty helpful, although a few things are a bit foggy, I got a 59 poncho parts car that i was going to pull the rearend out of before i sent it off, but it appears to be an open drive, is it easy to convert it to posi or do i have to buy a whole 'nother 3rd member? also if i use it i am probably going to have to narrow it since its a widetrack, does anyone make custom axles for those rearends that would have 5x4.75 bolt pattern? just wondering if this rear is worth my time or if i should just leave it well enough alone...

 

Dude, don't be so new. Pull that rear end out and then figure out what to do. As far as narrowing your rear it all depends on the car that it's going into. Yes posi's are available. And yes it's well worth your time.

 

well thanks R., good thing by the time i got back on here I already had the car up in the air ready to pull the rear. not sure what its going in yet, possibly my 54 PU, but can guarantee whatever it is aint nearly as wide as my 59. i guess it will just have to hang out in the shop while i do some more research. just thought if anyone had any quick answers off the top of their head, i never built a rearend before. im a fab man not a mechanic, but i am trying to learn.

 

looks like i will be doing some shopping at Fabcraft...

 

ok the extra pumpkin i had that i was talking about earlier in this thread.it has 3.92 gears but it is a 10 spline unit and i have late 56 rear 16 spline axles.if i took the ring and pinion out of the third member could i install it in my 56 third member housing.?the difference i noticed was the u-joint yoke was shorter.were all pinions the same lenght for 56 and earlier?want to install the 3.92's

 

Another great info thread!

As for narrowing one, You bet ! Stronger than a 9", and better gear selection than most other types of rearends. That is why i am putting one under my 1800+hp 69 Firebird dragcar with the new even beefier alum. center section.

 

The 516744 rear is a 1955 unit. It was cast on May 22nd 1955 .
The 506925 unit is probably an early 1948 unit and was cast on Aug 21st 1947.
All late 47 to 56 carriers will interchange in 47-56 axle housings.
The Pontiac parts book shows the same u-joint yoke used from late 47 to 55. It used a "mechanics" type u-joint that bolted directly to the flange. 56 used a different yoke that retained the u-joint with "U" bolts. It's possible that someone may have swapped yokes. In any case late 47 to 56 yokes will all interchange.
Differential side gears are all the same from 37-56 so axle spline count won't be a problem like the later 57-64 rears. None of the 37 to 56 rears were ever equipped with positraction, although some aftermarket "spools" may have been made.
By the way, If I were you, I wouldn't plan on any serious drag racing with any more than 300 HP with these rears. They don't have anywhere near the torque capacity of the 57-64 rears. Casual street use will be just fine.

 

Hey, I just got offered last night a 1964 Olds. rear with 31 spline axles, 3.42 gears and a posi for $600. Deal?

 

You bought it, right?

 

He's going to hold it for me 'til the end of the month when I get paid. Or if anybody needs a core 454?

 

I hate going every other week for paychecks, but monthly must really be tough!!! Yeah, I'm a huge fan of the 57-64 Olds/Pontiac rearend, which is I guess why I am doing the new center sections.

 

Just picked up a 3 rib center section w/ 4:56's and a spool + Summers Brothers 31 spline axles.............for $300. Everything went right in my 57 housing. Good deal?

 

Smokin' deal you got there. Any plans on racing your 55 Chevy?

 

I just posted a 1958 Olds. Pontiac rear for sale in our classifieds.

 

I'm confused about the 16 spline axle. All the parts books I have available are Pontiac. And they say that the differential spider gears were all the same from 37 to 56 which if memory serves me correctly were 10 spline. Could it be that Olds used a different spline count on some of their later axle shafts? Possibly so. If so, it may be possible to trade spider gearsets from the 3.23 rear into the 3.90. However, I can't confirm this.
It is possible to remove the spider gears without disassembling anything else. You simply remove the center pin (held in by a lockbolt) and rotate the entire gearset to the window so you can remove one gear at a time. Then you slide the side gears toward the center and pull them out. All gears and washers should be replaced as a SET and all components should remain in their respective positions when possible.
It is not possible to swap ring and pinion sets between the two differentials. The 3.08 to 3.42 diffs used a different diff case (the part the ring gear bolts to, not the pumpkin housing) than did the 3.90 to 4.55 cases.
The 3.23 rear that you have checks out to a 55 Pontiac by it's casting numbers. However, all of it's components may not be 55 Pontiac. Junkmen, in particular, were very adept at assembling a unit from whatever they had lying around in order to make a sale.
In closing I might suggest that you try swapping the yoke and spider gearset from the 3.23 pumpkin into the 3.90 pumpkin. Through careful comparison and measurement it may just work. Good luck!

 

well what i am probably going to do is find another diff with low gears that is correct for my rear.wanted to swap gears out for when i go far or when it is street driven change to low gears.my motor is pushing more then 300 this rear end is holding up just fine.thanks for the info

 

Hmmm, probably already gone...if anybody has one, I'm new on the thread, but looking for a Safe-T-Track Posi for my 1964 GP...Thanks

 

Hoping someone who knows these units can help me. I have a 55 olds rear that I want to put some lowering blocks on. Does anyone know off the top of their head the U bolt thread and size ( think 1/2 UNF) and the locating pin diameter ( again think 1/2).

I know I'm being a little lazy, I would like to order the lowering blocks this week and get to it on the weekend. I can find the info from dropping one side of the diff, but I wont be able to do that until the weekend, was hoping someone might know this off the top of their head so I can do the job in one go.

Also will the stock 55 diff hold up for a 455, being I don't punish it too much?

thanks.

 

I may have missed it but where is the gear ratio # stamped? I looked at my 2 57s and could not find it. Mine are supposed to be OLDS but measure too wide, may be Ponts. Thanx, Dave

 

Identify one more please.. I'm pretty sure I have it narrowed down to a pre-57 axle, but if possible would like to know what year exactly.

I think the number on the carrier is 51328(or 6)1

measured approx. 55" from axle housing flange to flange

 

I have a 1964 Pontiac rear to go in my '55. I'm doing a 1965 period build. I understand that rearends were not typically narrrowed. Is that right?

 

Depends on if you had the money or resources to do it back then...Pontiac axles are tapered, so they're much more of a pain in the ass to shorten and respline the axles...

 

I would like to know also?....I have one that is a posi out of the Gold Rush gasser sedan from 1966.

 

Revhead, From the info I got on the HAMB and some other research I would say your rear is the less desirable 1956 & earlier unit. It's difficult to see from your pictures but if the center section is not completely round (oblong) you have the earlier rear.

 

Great info. Been looking for this info.

 

Well I have this 1964 rear end with 3.42 gears and a posi that is going in my '55. I want my rear tires to just come a 1/4 in. past the lip so I'll have to measure my car and measure the rear end and wheels to make sure.

I guess that's right? Yeah makes sense to me.

 

Yeah, I think it is the "less desirable" one. I have a '58 converted to 31 splines in the garage and it is just too big IMO for my A roadster. I was looking for identification just for the purpose of ordering parts. I'm assuming it should be strong enough for a mild pontiac 347 in a Model A.

 

Here we go with the Model A debate again. If you want to put your wheels in the middle of your rear fenders the you want the rearend to measure 49" at the inside of the backing plates. A Ford Maverick 8" rear works great and if you get a V8 rear with 5 lugs it will handle a 347 nicely.

 

Who's debating? I don't have any fenders, much less rear ones. I pulled this rear out from under a '36 ford 2dr sedan, so it is what I have. If it is too wide I'll use something else, but I wasn't debating about anything, just trying to identify it.