I'm currently restoring my '65 Malibu SS that came with a 283 engine and Powerglide tranny. I moving up to a 327 + .060 and a Muncie M21 close ratio box. The 10 bolt differential code is stamped "CA" so it is a 3.08 ratio and non-positraction. I have a feeling that the transmission's 220 1st gear ratio is going to "lug" the engine some and I really don't have interest in smoking just 1 tire so I need to move up to a positraction unit (probably Eaton). Maybe a 3.55 to 3.70 ring/pinion ratio.

Now, the real question. Can anyone out there definitely tell me what type of differential that the 1965 SS originally came with? Some people have told be that I have a 8.5 differential and others say the '65 Chevelle came with a 8.2. My research has found that the 8.2 is basically useless under any real horsepower loaad but the 8.5 differential is serviceable if upgraded to 30 spline axles. There seem to be an ample supply of posi units available for the 8.5 so I would like to go that way if possible.

Help...and THANKS!

KD's65SS

Unless the rearend has been replaced, it should be a 8.2. The 8.5 did not come out until later. According to the Summit catalog a 8.2 has 25 to 27 splines on pinion and the 8.5 has 30 splines. To tell what you have, get under car and see if you can count the splines on the pinion. There is probably a buildup of grease/dirt around nut so it will have to be removed first. This is the only way I know to check. Maybe some else has another seggestion.

The '65 Chevelle had the 8.2 10 bolt with a 25 spline pinion and 28 spline axles. The 8.5 was not produced until '71. The 8.2 with an Eaton Posi, good gears, bearings and axles is strong enough for a 327 street engine. The gears must be set up correctly or it will break with a 4 cylinder. A 3.55 gear would work well with the 2.20 Muncie.

Thanks Guys! You've been a big help. I'll look into the price & availability of the 8.2 components. If this is the way that I decide to go, I'll find a professional to set up the rear end right. I guess the rear end's notched differential cover threw me off a bit.

The 8.2 and 8.5 covers will interchange. Does yours have the square lugs at the 5 and 7 o'clock positions?

Go for an 8.5 or 12 bolt, dont waste your time with an 8.2. I put more time and money into an 8.2 than it was worth. Trust me dont bother with it you'll kick yourself in the end

If it matters to anyone. I found and rebuilt the 71 12 bolt w/411 gears for my LS 454. Its so pretty sitting on the rack waiting to go in.
Point of the story:
The 70' 8.2 10 bolt that was in car when I bought it w/eaton 4:10 posi,30 spline axels, and T/A girdle just wont break! It has survived behind the 440HP/510Lb ft LS5 for over a year now. I took off cover and inspected myself and then had a shop inspect and they said whoever set this up knew what they were doing as it has perfect mesh and no signs of eminent breakage. They said any competent shop can set up any 8.2/8.5 10bolt to withstand up to 450 rear wheel horspower but it aint no 12 bolt either they said.