Looking for help to id this 10 bolt rear end pulled from a 75 Cutlass, I’m not sure it was original. Motor was 69 455, transmission 79 th400.
12” drums on it
like to id it so I can sell it
I think it is an 8.5 but cover has an oil plug on it???
i do know it is a 3:23 posi by the # of rotations
thanks
Jeff

 

There should be a casting number on the center section near the pinion flange. That number will ID it for sure.

 

Thanks I will check it out

 

EDIT.... If you say you pulled it from a 1975 it could be original to that car...as GM did have these as HD rears for the A body cars also 454 Montes, 455 cutlass and Grand prixs etc. Some were even 31 spline axles.
BEST if you open the rear cover- wipe the ring gear edge to see the tooth count stamped into the ring gear edge.
PLUS people will likely want to see the inside if your going to sell too.
NORMALLY- this is what they are found in:
GM 1978-1987 Wagon rear / Full size car it was the HD GM rear of the day.
Cover is a dead give away with the oil check and fill plug.
8.75 ring has a 8.5 pinion shaft (1.625) diameter, 30 spline pinion yoke.
usually 28 spline by this time.
12 bolt ring gear 7/16" x 20 left hand thread bolts
Caddy Deville had them also Chevy wagons, olds pontiac buick wagons
Full size cars with tow package got them.
TROUBLE...No posi units , No gears...
It was derived from the PONTIAC 8.875 full size car rear with bolt in axles back in the day.
Good strong rear...JUST NO AFTERMARKET SUPPORT...

 

Monzaz, I pulled the cover and ring gear is 12 bolt.
ring gear is 42 13gm 0zc97 N which is 3:23 gears.

So I have Gm 8.5 HD rear end with 3:23 gears with posi as per the pictures attached, correct??
so the 3:23 12 bolt ring in the unit is difficult to find??
thanks
Jeff

 

No, You have a 8.75 rear end with a limited slip.

 

Yes, you have one of the better gear ratios you can get in this 8.75 rear. 1978 -1988 era
Still would be nice to see if it might be 31 or regular 28 spline.

 

How can I tell what spline it is by not being too intrusive ?
Jeff

 

what is the casting number on the posi case? 17-1 17-2 17-3 17-4 ???

 

best way is to unscrew the retaining bolt (5/16 or 8mm headed ) that holds the main pinion cross shaft the spider gears spin on ...slide it out, then push the axle shaft in remove the c-clip and pull the axle shaft and count splines. Only other true way.

 

I removed the bearing cap, removed the pin retainer bolt , slid axle inwards, removed c clip , removed axle and counted the splines
28 splines
not too bad once you do it. Never done it before.
Thanks

 

Good job...

 

Mechanic stuff is mostly a memory game and being able to use your tools.
It is satisfying to be able to do this stuff yourself.