First of all I ahev 2 rears:
-2.7x posi with drums 10-bolt (from 88)
-2.7x open with disks 9-bolt (from 86)

I want to switch to the posi rear but want to keep the disks. Is it possible at all or are the bolt patterns different?

-Max

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86 Trans Am LB9/700R4
-Flowmaster 3inch exhaust, K&N, Ported Plenum, Redone Ignition system

 

Yes and no. If you have access to a machine shop then yes you can machine the flanges of the drum brake axles to accept the disc rotors. Sorry, I'm too lazy to dig out my drum rear from behind my storage shed to get the dimension, but as I recall the disc brake flange with the wheel studs in it is about half an inch smaller in diameter than the drum brake one. The disc brake axle flange measures 5-7/8". Next you'll either have to drill new holes in the disc brake backing plates to mount them to the two bottom holes on the drum brake rear or weld them to the housing. Custom fabricating them is another option. You would need to swap the brake lines from the disc rear to the drum as well. If you don't have access to a machine shop, then swapping the entire rear end is a much easier and cheaper route. I chose to swap the entire rear end since mine was a 2.73 10 bolt non-posi drum rear end. You may need to swap the proportioning valve as well. Early drum brake p.v.'s had a cast body that has a line coming out of the front. Disc and later drum p.v.'s are machined from an aluminum extrusion and have the line coming from the bottom. It is better to swap that line as well, but some people have carefully rebent theirs succesfully. Good luck, Lon.

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90 RS Convertible
Owner: Top-Down Solutions
http://www.sc3gfb.org/members/lonsal.html
http://www.taskerinc.com/gs3/profiles/Lon_profile.htm

 

you should be able to take the drum axles and have the ends (the flang with the lugs) turned down to fit in side the rotor you can do this by just mesuring the disc axle flang and making the drum one the same or just smaller will be even better(they are a tight fit from the factory) next mesure the axle housing flange I belive you can just cut the top off (where the wheel cylinder goes) and drill the two upper holes and It should bolt right up. of course "mesure twice cut once" this will be very fast and easy way of doing this I almost did it to my old drum housing but, got a great deal on a 10 bolt disc.

 

Well, this sounds like more work then I am willing to do. I am going to a junkyard this weekend and I'll pick myself up a nice posi/disc/3.xx axle.

BTW What models do I ahev the best chance to find posi/disc/3.xx combo. I am guessing 90-92 Z's and TA's?

-Max

 

3.73/posi/disc; that's a toughie; look for an 83-85 Trans Am or Z28. Lean towards 84-85; the '83's have standard (SAE) brake line fittings, while all 84-up's have metric. You could still use an 83 axle; you'd just have to find some kind of adapter, or bend/flare your own custom lines (with a metric fitting on one end and SAE on the other).

If you stumble onto the car I did... look for an '84 Trans Am, with engine code "G" (think "gold"), and a manual transmission. Chances are good it's got rear discs.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

I found my disc rear in a 84 Z28 I basically just used the housing and calipers every thing else I switched from my other rear. I had a new posi in my drum rear and used 3.73 gears from an s-10.