1993 GTP Brake problem Help!!

[Boneyard]

I've got a 93 GTP (3.4L) with anti-lock brakes that I'm using for a race car. The problem is the brakes are not very good on it, I can't get any rear brake and not a great front brake. Actually, I'm not sure if the front brakes are bad, I just know that the car doesn't stop very well and I'm getting nothing from the rear. The back lines are fine, I've tried bleeding them, changed calipers and can get nothing. Is this just a bad master cylinder or is there something else I could try. There is only two lines coming out of the master cylinder and some funky line underneath that goes to ???. If it's a bad m.c. so be it, but is there maybe something I'm missing. any help greatly appreciated. thanks

[TEAM_BRIAN]

SAME EXACT PROBLEM... I have a 93 SE 3.4 litre with brake problems. It just doesn't stop quickly enough. I don't have anti-lock brakes though but my brakes won't lock up anyway and stop very slow. I have almost rear-ended other cars like a million times because of this, and i have no idea why the brakes are in this condition. Anyone else have a clue???

[corning_d3]

Maybe your slack adjusters for the rear aren't working.

[BlueGT02]

When you bleed them are you bleeding the fronts too, cause the right rear is on the same system as the left front and the right front is on the same system as the left rear.

on my 94' i had to vaccum bleed the brakes 3 times to get the pedal to feel and work correctly,

also do you have 4 wheel disc, or do you have rear drums

[richtazz]

There is a reset button on the proportioning valve that may need to be pushied. If the system loses pressure, the proportioning valve shuts off flow to the offending corner and it's opposite. These cars are cross valved (LF-RR and RF-LR) so if the porportioning valve tripped, you only have brake line pressure at two wheels.

[Boneyard]

This Grand Prix has only two brake lines coming out of the master cylinder. Only one line heads toward the back, therefore they don't pair up with the front brakes (maybe they aren't abs, but there is an abs light on in the dash) They split toward the back. The back has disc brakes (which don't work at all).

[richtazz]

If your car is a 93, it has 4 lines coming off the master cylinder. Two come off the side, and two come off at an angle from the bottom. The two hex shaped "nuts" on the master cylinder near where the lines come off are the proportioning valves, and the left front and right rear are controlled by the one toward the front of the car and the right front and left rear are controlled by the one toward the rear of the car. The two rear lines run parrallel to each other and split just in front of the rear axle.

[Boneyard]

richtazz-appreciate the help-couple of things-if the front and rear are paired off, why do I have front brakes and no rears? I'm pretty sure that this GP is a '93, (it's not here at my house but at the shop), but if it's older could the brake system be different? And finally-how do I fix it?? thanks again for the help!