86 Audi coupe What else do I have to change when converting from drum to disc brakes. more details>?

Question

I am a professional mechanic so i know it can be done. I just need to know if anyone else has done this and if they ran into any problems. I have a 86 audi coupe GT with rear drums and I know a rear axel from an 88 80 or 90 will bolt right on( rear disc). the problem is with the master cylinder. I know i cant use the original. but will a master from an 80 or 90 fit on the 86 coupe and still work the front brakes with the proper pressure. anyone have a clue or know a website where audi owners swap info like this. the proper rear shoes are getting hard to find and the parking brake is really weak with this setup. Remember, I'm a professional mechanic with many best answers so NO RETARDS ALLOWED. If you cant help, keep your mouth shut.

Answer 1

Congratulations on a rare car! I had an '83 CGT for many years.

The cheapest, easiest and most sensible thing to do would be to buy an '87.5 Coupe which already came with disc brakes, plus a larger and more powerful engine (and an odd, love-it-or-hate-it digital dash). Audi Coupes, sad to say, are essentially worthless -- oh, sorry, "seriously undervalued by an ignorant car-buying public who doesn't understand their value." (I love them, but it's basically down to you, me, and this guy I know in San Jose who understand why they're so cool.)

Having said that... the NEXT cheapest/most reasonable thing would be to find an '87.5 in a junkyard and swap out the whole braking system (not forgetting the little rear-brake biasing switch just in front of the right rear trailing arm). Take the motor, too -- it's a higher-compression 2.3L five-cylinder, with more torque as well as more power (130, if memory serves -- a hefty jolt up from the 100 in my 2.1L version. The last '87.5 I drove, the one belonging to the guy in San Jose I was talking about, was a LOT more punchy than mine.)

Barring that, you can swap in the entire braking system from an Eighties 80 or 90 (FWD, obviously) -- get the fronts, too, the front discs are larger (I have a set in my garage, a planned track upgrade I never installed on my CGT.)

You may also need to snag the wheels from your donor car. I know that my '83 used 4 x 100 bolt pattern wheels (same as contemporary VWs), and I know that the post-87.5 Audis used 4 x 108 wheels (same as my Alfas), but I DON'T remember when they changed over, so I'm not sure which size your car uses. Take along a set of calipers when you're junkyard hunting.

The thing is... the drum brakes on the early Coupes aren't a problem, except that ricers will laugh if you have rims with big spaces between the spokes and they see drums instead of red-lacquered calipers and cross-drilled rotors. There's so little weight on the rear wheels in our Coupes that even for high-speed track work, the drums work perfectly well and give a fine balance. (Which is why the 80/90 upgrade also included larger front discs, so that the car doesn't snap around on you when you slam on the brakes.)

Now, if you've already dropped in a low-pressure turbo from a 5000T, or maybe the entire 20V turbo from a junkyard 200T, and you're planning on doing a lot of track time with R-compound tires, then yes, you might really be justified in upgrading the rear brakes. But otherwise... rear discs are really just bling on these cars, and your money and time is much better spent in other areas (like that junkyard turbo swap, for instance -- the I5 crank and rods are good for 300BHP, though your tranny isn't).

And THAT is the honest, non-retard truth.

Answer 2

definite the front drum brakes may be switched over to disk. the conversion calls for that the spindles, proportioning valve, carry close cylinder and power booster(if power brake) get replaced. the spindles would nicely be used yet all different elements should be offered new. i trust you should use similar 3 hundred and sixty 5 days LTD or Galaxie elements yet i'm not helpful so verify with a Ford save or a recking backyard that sells used elements both might want to be able to verify this. replacing basically the drum brakes to disc brakes with out replacing the proportioning valve and carry close cylinder does not be a secure conversion. disc brake are extra efficient and require a lot less pressure that drum brake so a proportioning valve used for drum brakes at the same time as used for disc brakes would reason uneven braking. also disc brake require a significantly better quantity of brake fluid that drum brakes. this calls for the carry close cylinder get replaced. if safe practices is your important situation do all or none!