posi rearend id help requested

[Guest]

I have a complete rearend from a '77 88 or 98; I forget which--it has been 15 yrs since I pulled it. It is a posi. The stamped code on the pass side tube is: 7 KZ B309 1. The casting number on the diff housing is 1251502, left side; GM42 on the right side The cover looks like 8.5 covers; it has the scallops on the sides.

What I would like to know is: is this a 8.5 rear end? It only has about 100,000 on it. It was behind a 403/turbo 400. I am not sure what I am going to do with the rearend. I am hoping to ID it without pulling the cover. That way, if it is an 8.5; and if I do decide to sell it, I can say it hasn't been opened and messed with. Any help would be appreciated. Thanks.

[Sgt Art]

Here's what I found on Olds FAQs:

The 442 and Regal axles are hard to find because 442s are rare and most T-types and Grand Nationals are not junked yet. For older Cutlasses, the B-body 8.5" axle might fit better than the G-body axle.

RPO |--------Axle Code--------|

Ring Gear Code Ratio Conventional Limited Slip

-------------------------------------------------------

7.5" G72 2.14 2AK 2BK (aluminum brake drums)

7.5" GH2 2.29 2AH 2BH

7.5" GU1 2.41 2AJ,2AZ 2BJ,2BZ

7.5" GM8 2.56 2AA 2BA

7.5" GU2 2.73 2AB,2AX 2BB,2BX

7.5" GU4 3.08 2AC,2AV 2BC,2BV

7.5" GU5 3.23 2AD 2BD

7.625" GT4 3.73 2TF 2TH (Monte Carlo SS)

8.5" GU6 3.42 3TP 3TJ (T-Type, GN Std.)

8.5" GT4 3.73 3TG,3TE 3TR,3TX (442, GN Opt.)

8.5" GU2 2.73 8YB 8YP (B-Body)

8.5" GU4 3.08 8YD 8YR (B-Body)

8.5" GU5 3.23 8YE 8YS (B-Body)

If you don't have the codes with you to indentify if it is an 8.5" or not, I found that if you measure the distance between the very bottom bolt for the cover and the next adjacent one (either right of left), it will be 3 ¾" for a 8.5" and 3 1/4" for a 7.5".

All 1978 and up Olds came with 7.5" 10 bolts, no 12 bolts (Chevy or Olds) whatsoever. So guys with 1978 and up G bodies had a few options: beef up the 7.5" with better axles and a good posi unit, or find an 8.5" out of an 83-84 HO, 85-85 442, or 84 and up T-Type or GN, or go with a Ford 9" from Currie or Moser, or buy the control arms from Southside traction and install an older 1968 or so Chevy 12 bolt or 10 bolt.