I also have an '88 Jetta TD and when I got it the brakes were almost nonexistant due to a bad master cylinder. I beleive it was a 21mm but starting on the Scirocco 16v and carrying over into the MK3 Golf/Jetta they started using a 22mm master cylinder. It decreases the amount of pedal travel required to stop the car though it may reduce the resolution (for lack of a better word) in the brake pedal. This is a direct swap onto most if not all MK2's. Stock the car had 9.4" solid front rotors and rear drum brakes which can easily fade on the twisties. I replaced the front knuckles with those from a 2L MK3 and then used the 10.1" MK3 brakes. I also swapped on the rear disk brakes from a MK2 (The MK3 rear brakes should also work but you must use the MK2 e-brake cables). It stops much better now but in order to move up to the 10.1" brakes you must be running a 14" or larger wheel. If you want even more then the 11" G60 brakes will also bolt onto the MK3/Passat/G60 knuckles. The stock knuckles used with the 9.4" brakes are not upgradeable. I hope that helps you out a bit.
the braking in a correctly-setup older VW (75-92) is phenomenal. i was out in my friends 91 16v GTI last week (stock brakes) and almost put us through the windshield while testing out the brakes :lol: