What all do I need to cover to swap the rear end in my car? I can get a disc posi 3.23 from a '91 Z28 and want to swap it into my '85 Z28. The car currently has a 3.08 one leg axle with drum brakes. I guess I need to change the master cylinder for the discs and will need to change the driven gear in the tranny for the speedo - anything else? Handbrake cable? Brake hoses? Uni joints? Will it bolt right up?

 

the rear will bolt right up so will the u joint, unless one has aluminum drive shaft, then i'm not sure. you'll need porpotioning valve, not master cylinder. if you have the flat sided macnined looking aluminum one it ought to work, but if you have the round cast looking one it ought to be replaced. a lot of people don't replace anything and get by. not sure if you'll have any clearance issues with your wheels, i'd guess not.

 

I can't recall when they changed from SAE to metric brake line fittings, but you may need to deal with that.

When I put a 91-92 disk brake rear in my 83, I got the last 10' or so long piece of line with the fitting, and spliced it onto my SAE line with a flare fitting. Parking brake cables hooked right up. I did not have to replace my MC or prop valve but you may have to change the prop valve in your car, there are a couple of varieties. IIRC in the later cars the drum & disk rear brakes both used the same ones of those however.

I have 87 IROC 16" wheels on my car, they fit about the same before and after. Don't know about the old 15" like your car would have come with.

Like ede said, the U-joint yoke will be the same.

You will need to change the speedo driven gear at least, maybe the drive gear, it depends on what's there now.

 

I'd love rear discs...but for now I looking at deeper gears.

Any thoughts on the right ratio for a street car that sees a fare amount of interstate?

My 2.73's are great for 95 MPH cruise, but kill me in first gear.

 

Depends on your motor among other things; 3.42 is a generally good ratio for these cars