Hello. I am miffed with my braking problem. I am hoping someone might be able to help me. I have 1994 c4 vette with LT1 ABS/ASR. My problem is I occasionally(3 times over past month) lose ALL brake pedal (to the floor)after driving car for a while. 2 of 3 times I lost pedal I turned car off and waited for a few minutes then pedal returned...pumping pedal didnt work and NO dash BRAKE warning light activated. The last time it did it was yesterday but this time I was able to pump pedal to get back some brake pedal only for it to sink again to floor on next stopping pedal push...then pump again to get back about half way(this continued for few miles). The dash BRAKE light illuminated shortly after pedal failure only to go off after a few miles then pedal was back up again and stayed up for rest of drive. The problem has happened b4 so I replaced the master cylinder with new delco master cyl and after that I replaced the power brake booster as well with new delco. REMEMBER this problem occurred b4 replacing any parts but has continued since. There is no loss of brake fluid in the system, at wheels or or lines, master. Master cyl stays full. SO ...my question is: is this a symptom of a needed ABS brake fluid bleed by dealer? or does it sound like an ABS modulator/actuator failure? Also when brakes are working the brake pedal also feels very tight/hard always when pushing as if the power brakes are some what off but still stops car ok... just fyi in case this sheds more light on problem. Also good vacuum to booster. PLEASE any ideas would certainly help. I want to see if I can fix b4 heading to dealer but need a direction on what might be wrong. ALSO no tripped trouble codes or ABS/ASR warning lights.Thanks again for any help you can offer. ONE final note...bled system at wheels and bench bled master on install...but not the ABS modulator.

 

I understand your frustration and need for a prompt solution, but it might help if you fill out your profile or at least tell us your location. Several members have Tech1 scan tools and might save you a trip to the dealer if they happen to be close by, myself included.
This might be grasping at straws but I will toss it out there. Have you made any exhaust changes or heard any leaks since the problem began? I have seen such intermittent loss of pedal and return to normal if a brake line comes in contact with the exhaust or hot exhaust gas is directed at a line. This can cause the fluid to boil causing pedal drop, once it cools the pedal returns. Certainly not common, but one possibility to consider since you have already replaced the master, good luck.

 

I havent made any exhaust mods...completely stock. The advice on the heat problem near the brake lines certainly is an idea to visit. I also kept thinking that might be something to look at due to the problem occurring only after driving the car a while and as I recall the earlier events only after the car was at hwy speeds then slowing down it happens. I will look around and see if something might be too close to an exhaust part. The only thing that is interesting with that is the dash warning BRAKE light going off...not sure what that would trip to set light off other than a pressure drop which might be the trip detail Thank you and I will get back to you on that after I check it. I bet your right!

 

Sounds to me like you have air in the system, a bad master cyl, or your loosing pressure somewhere.
The ABS system will not cause you to loose all pressure. Even if the ABS system was completly bad, and unhooked the system will still hold pressure.

It could be becuase of exhaust causing the fluid to heat like mentioned above.