Front Brakes Lock Up after a few stops
 

My front brakes lock up after a few stops. This is so bad that the car comes to a complete stop and can't be driven. If a wait a few hours the brakes release by themselves.

I have replaced both front brake lines but the problem still remains. If I crack either front bleeder screw both sides release. This would seem to indicate a problem with the master cylinder or the ABS unit.

The car is a 94 with 18k miles. The problem occurred when the car sat in storage for about a year.

My current theory is that if I crack one of the lines at the master cylinder and the brakes release, then it is probably the master cylinder causing the problem. If they don't release, then its probably the ABS unit.

I would appreciate it if someone could let me know if this approach makes sense and any other likely causes.

Also if anyone has a diagram of the brake line routing from the Master cylinder down to the ASR and ABS unit the brake calipers, it would be useful.

Re: Front Brakes Lock Up after a few stops
 

Its the master cylinder

Re: Front Brakes Lock Up after a few stops
 

:happy1:

Re: Front Brakes Lock Up after a few stops
 

Thanks, I just ordered one and will post the results once I install it.

Re: Front Brakes Lock Up after a few stops
 

It was the master cylinder. I replaced it and the lock up problem is solved. I now have the red brake light in the instrument cluster illuminated. Apparently there are 3 things that can cause this.

Parking brake switch .... didn't mess with it

Low Fluid warning switch

Brake pressure switch

A little more diagnosis is necessary.

I found this post which was helpful https://www.corvetteforum.com/forums...-light-c4.html

Re: Front Brakes Lock Up after a few stops
 

Did you reconnect everything? bleed the system top off brake fluids??

Re: Front Brakes Lock Up after a few stops
 

I've been fighting this a while on a buddy's car. It is most likely the proportioning valve that repositioned while bleeding (air in system). I have one more trick up my sleeve before I throw in the towel.

Turn key on--don't crank. Make sure parking brake is off. Then unplug switch on mater cylinder on the proportioning valve cylinder (the white switch you traded out). Did brake light go out?

Ted