══════════════Frequently Asked Question════════

Author: Pioneer63
Reason: topic
My personal experience on the interchangeability of 70s GTC and vacuum booster with a 90s booster.
So, friends and fellow enthusiasts, Mark has some minor issues with his brakes, specifically after adjusting the rear wheel alignment, my brakes started acting up. The problem is that during winter when I was doing the adjustment, I had to remove the rear control arms and naturally disconnected the brake hoses. Since it wasn't an urgent job, the braking system got clogged somehow and upon testing, things went haywire; the brakes simply wouldn't inflate properly. I took out the GTC, cleaned and blew through it but it didn’t help much. With the front GTC, when pressing down on the piston, brake fluid would spurt up to the ceiling as expected, but nothing from the rear one. After disassembling and injecting fluid directly into the GTC with a syringe, it seemed to have helped. I reinstalled everything, and initially things were back to normal. However, during driving trips, it was discovered that over time, the front brake circuit would start binding (re-flushing did not resolve this issue). Eventually, I got tired of it and continued driving as is: after about 15-20 minutes of driving when you feel the front starts binding, pull over to slightly drain off the brake fluid from the rear right wheel’s caliper. This allows the pads to separate (you can hear the pistons retracting), allowing me to continue. Of course, this became quite annoying for me and due to lack of time, I didn't have proper resolution.
I then examined a GTC with vacuum booster at Cross, compared and measured them; they seemed almost identical, just slightly shorter in length and position differences on the fittings but these can be adjusted. So, I ordered one. Upon arrival, I took off mine and installed the 90’s model (important note: it was from GX-90, NON-TURBO! Turbo versions have a completely different setup requiring significant bending of pipes which complicates things!). Notably, the mounting bolts fit perfectly without any need for drilling or additional modifications. The shaft fitted nicely into the pedal as expected and everything just seemed to slot in place smoothly. I only had to slightly adjust the hoses for both front and rear circuits: the front hose needed minimal adjustment while the rear one required more extensive changes but nothing too complicated with patience.
Now, all that's left is to flush it again and test how things have changed (I believe the brakes should now feel softer but perhaps also better gripping, though I’m not sure - we’ll see).
P.s. I think this information would be useful for all 70’s models owners looking for parts related to GTC and vacuum booster.