'57 poncho rear ID

I bought a rear out of a '57 poncho. is there any way to determine the ratio without the rotate and count method. I need an accurate ratio,not a about. Its between 2.75 and 3.50 by the rotating method. Are the marked on the OUTSIDE?

 

Yes, unless you know it came out of a stock '57 Pontiac, make sure of what third member you have. If it's 1st generation, i.e., 1957/58, the casting number is 522496, which is located at the nine o'clock position as you're facing the pinion snout. Supposedly, the date code, an alphanumeric code consisting of a letter and either two or three digits, is located at the three o'clock position. Having said that, my date code was located next to the casting number at the nine o'clock position. So, you may have to hunt around for it. The letter corresponds to the month of the year. For example: A equals Jan, B equals Feb, etc. If it has three digits, the first two are the day of the month and the last is the year. On a pad near the bolt hole at the seven o'clock position will be a stamped number, zero thru nine (except "one"), and possibly the letter, "L". If the stamped number is followed by the letter, "L", it has the Safe-T-Track differential. The stamped numbers equate to the gear ratio as follows:

0 - 3:08
2 - 2:69
3 - 2:56
4 - 3:90
5 - 4:30
6 - 3:64
7 - 2:87
8 - 3:42
9 - 3:23

You may have to clean the third member off with degreaser and a wire brush to see the numbers clearly as many, such as six, eight, and nine, tend to look alike. Good hunting!

 

Won't find an L on a '57 housing, I've read in several places that it wasn't available in '57 and won't fit the case without mods and custom axles.

 

Well.... Pontiac and Olds limited-slip differentials weren't available until the 1958 model year, which was introduced in Sep 57. Therefore, it is possible to have a third member cast with a 1957 date code that was destined for a 1958 model car, which cud also have a stamped "L" on it. It gets crazy when you're trying to figure out just what you have, especially when you only have the part and not the car it came out of, or if you do have the car and don't know the history of the car.

 

Well, a '57 complete rear will have leaf spring perches on it and a '58 should have 4-link and coils, so ***uming you have the whole thing the difference will be pretty apparent.

The 59-64 posi is a lot easier to find, but as noted the splines on the axles differ and the width changes, particularly if it's out of a Pontiac. Moser used to make axles that would let you run it in the 57 housing, but I guess even those are hard to come by now.

Plus I'm going from memory from a couple sources -

 

Definately a '57 with leaf springs. I'll clean it uo to check ratio. Thanks to those that KNOW.

 

I also have a question about these rearends that somebody may be able to help me with - I need the measurement from the face of the axle where the wheel bolts on to the face of the axle housing flange where the bearing retainer bolts up.

Mine has aftermarket axles and no brakes yet. Trying make sure the axles are made to stock specs.

 

Fabcraft in Texas sells an excellent book on the 57-64 Olds/Pontiac rear ends. It has tons of info on the rear ends and will worth the money. However, I don't think the book mentions axle lengths or rear end widths. Other than that just about everything else you need to know is in it.


Dustin

 

You might try getting on the Performance Years (PY) forums (all Pontiac). You can find almost any Pontiac info there ...or someone who frequents there probably knows. The 61 and earlier section would be a good place to start your search.

 

I guess even those are hard to come by now.