hiperf 427

I have a pair of late C-3's that I'm putting together for my girlfriend and myself. Hers is a '79 with auto and mine is an '81 with a stick. Mine has numbers matching engine and tranny that will both be pulled and stored in favor of a rebuilt Super T-10 and a 500 or so horse 406. Her rear end gears have been changed to 3.90's which is way too high for the amount of highway miles we'll be putting on it. Mine is stock 3.08. Can I swap rear ends straight across or is this gonna open a big can or worms? I also plan to go to heavy duty U-joints and probably have hardened stub axles in the one with the stick. Any recommendations on which U-joints or stub axles to use would be appreciated!

Jvette73

I think there is a difference in the rears between those years. 68-79 are the same using a GM unit. 80-82 use a Dana unit. Im not sure if they are interchangeable.

Gordonm

:iagree: The two rears are totally different. they will not interchange.

hiperf 427

So, which is stronger? Could I swap the entire rear assembly, crossmember and all, if needed?
Thanks for your help!

Twin_Turbo

Mounting a 80-82 diff isn't that hard, it just requires 4 ears to be welded on the frame. positioning is simple too, just bolt up the lower pintion mount and put the diff in place and presto, you know where to put the ears. Might even chop them off a 80-82 frame.

The earlier diffs are a bit stronger than the 80-82 Dana44 but they can be built up to be pretty reliable. A 4 series case will fit if you want short gears. Polishing the case is a good way to eliminate stress risers. Clip or spring secured clutch plates don't matter, both will fit. The 80&81 manual and all 82 diffs have the stronger big block stubs (& half shafts if you get the complete rear)
The problem w/ the alu case is that the bearing caps for the case are mounted on an AS CAST surface in the diff case (the C4 D36 has that too, the C4 D44 has machined surfaces there). You'll need to properly set up the case by stretching it, these things have quite a bit of growth with temperature.
Tom shims the clutch pack to specs instead of spring/clip loading it. Then they turn the thing 50 times by hand (one stub clamped in a vise) to break in the clutches, then disassemble and finally shim to spec again.

Scooter70

Wow, Twin Turbo likes to fabricate things.... Me? I'd buy a rebuilt diff with 3.36 gears from a forum member. See the C3 parts For Sale section. There's a couple in there that will work. (One is mine.)