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    Help identifying rear axle

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    fourfiftyfive
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    Help identifying rear axle

    Post  fourfiftyfive on Mon Aug 03, 2015 9:45 pm

    Hello, I have a 93 caprice classic LO3 engine, 2.56 rear. I'm pretty certain it's a 7.5/7.625 rear (small horns on bottom of cover). My question is identifying the rear without disassembling it; for two reasons:

    (1) I drive this car daily, can't afford much down time

    (2) I have an S10 rear that is a 7.625 with 3.08 gears, and another S10 rear which is a 7.5 with either 3.23 or 3.42 gears (checked it the inaccurate way spinning the wheels and counting), either of which would provide a nice upgrade, and the price is right (free from the junk pile Very Happy )

    So, my question is how to identify which it is, so that (hopefully) I can get lucky with this thing and get a little more pick-up out of it.

    Thanks in advance.
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    Myloth
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    Re: Help identifying rear axle

    Post  Myloth on Tue Aug 04, 2015 11:46 am

    ! Having swapped from a 7.5 to a 8.5 from a 90s Roadmaster, swapping in the known to be very weak 7.625 could be a

    time waster. There are 8.5 Posi around granted I paid a pretty penny for mine but free is not always a good thing.

    You could go with a 7.625 but you'd be locked into a weak factory rear with no upgrade potential down the road.

    I wouldn't do it but it is free and if you think it's solid the 3.08s might be worth it, but don't consider the 7.5s they are

    really WEAK the 7.625 is OK with factory power levels and not too much abuse. I am no expert but I have killed enough

    Rearends to know which are weak ones rofl .
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    fourfiftyfive
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    Re: Help identifying rear axle

    Post  fourfiftyfive on Sat Aug 08, 2015 11:56 am

    Hey man I hear ya, I've been hunting around trying to find an 8.5, but this is a stock 305 car and my daily driver so I don't plan on making any serious power or abusing it. What I was really looking for information on is how to tell a 7.5 from a 7.625 without wasting too much time or opening it up.

    Who knows, maybe I'll find a decent 8.5 in the yards around here (they're rare here in the rust belt) and then maybe I'll make a home for that 350 in the garage...
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    Re: Help identifying rear axle

    Post  GM B-Body Forum on Sun Aug 09, 2015 3:21 pm

    Yeah theres no difference on the outside from the 7.5 to 7.6 only the inside bearings and ring and pinion are different, same with the 8.5 and 8.6. If your just using it for stock application, then thats fine, even though i destroyed mine with 2.41 gears with the stock motor. They are pretty weak but are found in millions of GM vehicles. Only way to accurately find the gear ratio with out the build sheet is to take the cover off and read the numbers on the ring gear. But since GM only put a few different ratios in them it should be hard to guess with a tachometer. I know they came with 2.41, 2.56, 2.73, 3.08, 3.23, 3.42, and i think thats it for the stock applications for both the 7.5 and 8.5. If you know what its coming out you can narrow down those gear ratios. If you havent yet check this out, but im sure youve already seen it https://www.gmbbodyforum.com/t333-how-to-id-your-rear-end-gm-10-12-bolts-7-5-8-5-8-75-8-875


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    1979 Caprice Sport Coupe, 400hp Vortec 350, Th350, GM 8.5 w/disc brakes, 3.90 gears Detroit Truetrac, 2.5" stainless duals w/ x-pipe, Dynomax race bullets.
    1984 Caprice Sedan, 305 motor, 700r4
    1978 Caprice Sedan, 305 motor, th350
    1993 L99 Caprice, 4.3 v8, 4l60 trans
    1972 Ford F-100, 302 windsor, c4 trans
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