I'm having poor braking on '88 GTU (same brakes -four piston- as the turbo). The car does not have ABS.

The problem is that the pedal goes halfway down before engaging.

First, about what's been done/info:

Brakes bled several times
Booster check valve is good
All four brakes are engaging
There is no external fluid leak- the Master Cylinder level is static

The pedal will rise higher if pumped, but then requires a lot of force to depress.

I'm guessing the problem is one of two things:

1. Internal Master Cylinder leak
2. A vacuum leak

Is it possible that a vacuum leak could cause this problem? Suggestions, insights?

 

Have you tried to adjust your brake booster pushrod? I have an 88 GTU and found that lengthening the brake booster pushrod will do the trick. You just have to be careful not to pull it out too far. Unbolt the master cylinder from the break booster. You can do it without removing the hydraulic lines.

There should be two 12 mm nuts and a 10 mm nut on that gray thingie. Pull the 10mm nut off and push the grey thingie aside before you get to the last 12mm nut. Then move the master cylinder out of the way and you should see the brake booster pushrod. You may have to pull it out a bit with a pliers. On the end is an adjusting screw that needs to be lengethened. Use a 7mm (at least I think it's 7mm) socket to lengthen the pushrod. You may need to use the vise grip to keep the adjusting screw from just turning pointlessly.

You you might want to pull it out just a couple millimeters. If you lengthen it too far the brakes will drag. After you lengthen it put the pushrod back in and bolt the master cylinder up. You should notice your pedal travel to be significantly shorter. You will have to play around with it and adjust it perhaps several times to get it just right so that the pedal travel is acceptable and the brakes don't drag.

 

Sweet. I'll give that a shot. Thanks.

 

is it like just plain hard to push? because if it is hard to push it may be a vacuum leak so you arent getting the help of the booster. And sometimes it could be the booster, such as an internal leak of somesort.

 

Woah more 88 GTU owners, this rocks! Oh yeah I had a problem like that on my car, but i couldn't brake for ****, look at the left side of your engine bay and look at your lim, at the left of that theres a vacuum line that connects to a metal line by the brake booster (I think thats it) I had a leak there and I had bad braking just like you did.

-Andrew