I believe that the 85 GTI uses mere 9-inch brakes like earlier cars. Only the 16V GTIs (of 1989-up) had the larger 10.1 inch brakes and Girling Calipers. These later calipers are what were used on the MK III cars as standard issue. Before that, only the 16V GTI, GLI and Scirocco had them.
But, as noted by others, the fronts are vented. Frankly, I've often found the solid rotors to brake better and be less prone to warping. But, that's just me. You may want to convert. BUT, there could be a problem there: the brake pad carriers on the 1985 are part of the spindle housing. You'd have to swap the spindles onto your Caddy. I can't remember if this is possible. I'm pretty sure the struts won't fit over the top of the spindle, and I think the lower ball joint is different size too. So, you may be SOL on the front brakes.
If you want to upgrade your fronts, I think you only bet would be to find some 16V Scirocco front calipers and carriers (hard to find these days). They will bolt right up to your front spindles, and they are 10.1 inch vented style Girling Calipers. While the calipers are all the same for 1989-up 16V cars and MKIII cars, only the Scirocco had the carriers that would bolt up to the MK 1 spindle. Contrary to popular belief, the other 16V and MKIII carriers will not.
The rear calipers will bolt right up. You'll need the stub axles and the backing plates to bolt them up to your rear axle. I do forsee a potential issue with the E-brake cables. Check the poortex. I'm sure someone has figured out a solution. Normally, you'd use Scirocco 16V cables on a Rabbit, but the truck cables are longer.
Also: the 1985-1988 rear calipers had the e-brake cable mounted to the TOP of the caliper. Later cars (1989-up) switched them to the bottom. I used to live in New England, and the early style ones were quite prone to siezure due to the fact that salty water would dribble down the e-brake shaft to the heart of the caliper. The caliper might work the brakes, but the E-brake part would do nothing. If you live in a road-salt zone or a rust zone, it may be a better idea to get some rear calipers off of a later car, and use the stub axles off this car (I may be wrong on this: thinking they interchange). Anyway, something to think about.
As for proportioning valve. Your truck should have one mounted to the rear axle, or just the simple one mounted in the engine bay. If you have the rear-axle style, then you may be able to adjust it (can't recall if it's adjustable: and I think only the 1980 truck had the axle-mounted one). If not, then 16v proportioning valves are a good idea.
Good luck!
Topic: Need Help! Rear Disc brake upgrade -1980 Caddy (Read 10388 times)
