96' LT1 Brake issue

[digimc]

About two months ago I had a soft brake pedal problem which resulted in the brake booster, master cylinder, ABS valve unit and one caliper being replaced. All was good after the replacement parts (about 300 miles) until I went to use the car today and while backing out of the garage found that I needed to apply major pressure to the pedal to stop the car. The pedal was rock hard! No sinking or rising pedal. I have proper vacuum at the booster and no hissing anywhere. The car rolls fine but is completely unsafe to drive as it is hard enough to stop at rolling speed much less highway.

The car has a total of 23000 miles and is well maintained although it sits on the storage lift too much. Any suggestions are appreciated.

 

[forrest]

About two months ago I had a soft brake pedal problem which resulted in the brake booster, master cylinder, ABS valve unit and one caliper being replaced. All was good after the replacement parts (about 300 miles) until I went to use the car today and while backing out of the garage found that I needed to apply major pressure to the pedal to stop the car. The pedal was rock hard! No sinking or rising pedal. I have proper vacuum at the booster and no hissing anywhere. The car rolls fine but is completely unsafe to drive as it is hard enough to stop at rolling speed much less highway.

The car has a total of 23000 miles and is well maintained although it sits on the storage lift too much. Any suggestions are appreciated.

This is totally from the hip, could you have a clogged brake portioning valve. Find someone to stand on the brake pedal and go crack the bleeders starting at the wheel end and working your way to the master, I suspect that you have reduced pressure to the fronts.

After thought before you start cracking bleeders, Question is the ABS pump doing its test cycle Constantly while moving slowly, or the normal 1 second test once moving?


If the pump keeps running it treats braking like your on ice and the car will not stop to well. making me lean more toward a bad wheel end ABS sensor.

 

[digimc]

I'm not sure how to tell if the ABS unit is going through a test cycle. I do not hear any chatter or feel any pulsing in the pedal. Also, I thought I would add that with a firm foot on the pedal and then starting the engine there is no change in the pedal position. Usually every other car I have done that with results in a slight depression of the pedal upon starting the engine. I wonder if it isn't a defective booster or bad pedal linkage to it. However, all was fine when I pulled into the garage last week. Annoying to say the least. This car will need to be flat bedded if it needs to go to the shop.

 

[forrest]

I'm not sure how to tell if the ABS unit is going through a test cycle. I do not hear any chatter or feel any pulsing in the pedal. Also, I thought I would add that with a firm foot on the pedal and then starting the engine there is no change in the pedal position. Usually every other car I have done that with results in a slight depression of the pedal upon starting the engine. I wonder if it isn't a defective booster or bad pedal linkage to it. However, all was fine when I pulled into the garage last week. Annoying to say the least. This car will need to be flat bedded if it needs to go to the shop.

when you tested for booster Vac. did you just pull the hose off the check valve or did you take the check valve out and see if the Vac. is getting into the booster

 

[digimc]

when you tested for booster Vac. did you just pull the hose off the check valve or did you take the check valve out and see if the Vac. is getting into the booster

Yes, I removed the check valve which is new and it was functioning properly.

 

[forrest]

Yes, I removed the check valve which is new and it was functioning properly.

I guess you could have a bad Booster since you say the pedal starts out high DOES NOT DROP when car is started, it has Vac into the booster, I would still try cracking the bleeders to test for blockages before just replacing it doesnt cost anything but some time and rags and a shot glass of brake fluid