Pre and post ‘83 are different due to the distance where the master bolts to the servo.
post ‘83 are all compatible with the exception of abs master cylinders. These can be adapted by blanking off ports if I remember but I cannot confirm how the bias will work on these abs ones
For reference, there is also 3 different rear cylinder sizes on the mk3 and a standardised middle one on the mk4. Altering these along with the different master cylinders can make a rear difference in how the brakes operate.
I run a 24mm master and 17.8mm rear cylinders on my mk4 Cabriolet with the larger xr/rs drums and 260mm front discs and have nice, balanced brakes.
Last edited by iansoutham; May 20, 2018 at 07:46 AM.