How can I tell what rear I got?

[drop the hammer]

Anyway yeah, Dont know what I got in the rear, I could identify any truck rear end chevy used by eye, the cars, no idea. Was told the rear end was out of a monte ss, but who knows. If it was I know the posi is shot, just wanna know what rear I got so I can replace the guts with deeper gears and posi.

 

[v8power]

if its out of the SS it is a garbage 7.5 dont stick any money into it because it is not worth it. find a chevelle 12 bolt, or 8.5 our of a GN or 442. or you could go the ford 9 way, but i dont really like them unless you are making mega HP's

 

[megaladon6]

x2 the g-body rear is not worth rebuilding unless it's the rare 8.5. even the larger than usual (by a whole 1/8in) monte ss rear isn't worth anuthing. the 8.5's can be found in the GN and 442.

 

[pontiacgp]

if you remove the differential cover you can find the number of teeth stamped on the pinion and crown...you divide the number of crown teeth into the number of pinion teeth and that'll give you the gear ratio...as far as the 7.5 diff we run them in a thunder car which has a 602 crate engine and of all the race cars in that division I think there was one car that had a differential failure so they are not garbage as someone described it....if that diff is out of a SS then if it was 84 and down it probably had a 342 and 85 and up SS has the 373

 

[82355supreme]

I agree with pontiacgp...... the 7.5 get a bad rap & it's complete BS. The average guy with a 400 HP engine (and that's at the crank NOT the wheels) in a street car/cruiser won't kill a 7.5"

If you're running at the strip every weekend with a 7.5", 500+ horse to the wheels, transbrake, on slicks, then you deserve a broken diff.

I personally know (friends of mine) of a '78 monte carlo that runs 11.30s consistantly and an '88 camaro that runs 10.80s consistantly, and they both have 7.5" diffs. The Monte has Auburn guts with stock axles & the camaro has Auburn guts & Moser axles. Both leave on foot brake.

 

[BrownGP83]

were all MC SS rears the 7.625 or were some 7.5?

 

[Furtrader]

Identification of a 7.5" vs. a 8.5" rear axle can be a little difficult if you don't know what to look for.

The 7.5" rear axle can be identified by the "fangs" on the bottom of the center section:

While the 8.5" rear axle can be identified by the "triangles" on the bottom of the center section:

...from oldsgmail.com

 

[85_SS]

were all MC SS rears the 7.625 or were some 7.5?

7.625" started in 85. To address one of the points in the first post - POSI was an option on the SS, and an educated guess would say about 30% of them actually had it. I've owned three, all with open rears.

 

[pontiacgp]

POSI was an option on the SS, and an educated guess would say about 30% of them actually had it

I can never understand why anyone would order an SS or any other performance car without a posi and on the other side of the coin how a car salesman couldn't convince someone who was interested in a performance car to buy that option ... :shock:

 

[85_SS]

I believe the main reason is most cars were dealer ordered. They ordered them with the fancy/flashy/comfort options that you can "see" like power doors/locks A/C etc. but usually didn't bother with something like a posi rear as it's added cost that isn't flashy. Most customers probably either didn't even know what a posi rear was, or didn't want to wait the extra 'X' amount of weeks/months to get their special ordered car with a posi rear when they could drive home the one sitting on the lot that day. Many people that bought these cars simply liked the look (there wasn't much in the way of stock performance in the 80's). I think you'd find that most cars that did have a posi rear, were customer ordered, much like cars that are more basic with manual windows and locks.

The real question is why it wasn't standard equipment on the performance models such as the SS, 442, GN, TR's Hurst Olds etc. It was a very cheap option too IIRC in the $100-150 range.