I have brake problems on my 89 sub 6.2 diesel. The hydroboost system builds up pressure in the brake system causing the brakes to go on. This happens more often when highway driving and not using the brakes much. The brake pedal becomes rock hard and the brakes heat up. Once the engine is shut off for a few minutes it the pedal recovers somewhat but is still rather high. Any Ideas or things to try would be a great help.


Thanks,


VB

Soft seal rings in 'boost have age\heat hardened, are leaking internally. Time for replacement - 'zone, NAPA, etc - check for best price.


Might also consider new hoses while it's down.Edited by: gmctd

Change my Hydroboost unit and still have the brakes getting very hard and I feel the truck is forcing like going up a steep hillcoming I pull over and stop. The brakes are stinking hot. I then stop the engine and discharge the accumulator by pressing the brakes a couple of times until the pedal is hard. I restart the engine with my foot on the pedal and I feel it drop and then push back against my foot as it should. The pedal then feels OK and I start driving again. It is better but the pedal still feels a little harder than it should. I continue on my trip and usually don't have to stop again as I don't feel much drag and the truck. I have only taken it out twice since the Hydroboost was replaced, both time it as done this.


I am very frustrated as I started out with a sinking pedel when stopped at a traffic light. I would have to pump it to keep the truck from creeping forward, I was told to replace the Master. After I replaced the master this hard pedal build up started to happen and I totaly smoked one caliper and burnt the seals off it trying to get off the highway when the pedal became rock hard. I then replaced the caliper and changed the pads on both sides. Still the pedal was getting hard. Changed the Hydroboost unit and still not much better.


I have gone from a sinking pedal to a rock hard one. I don't know what to do next.

Possibility the replacement 'boost unit is defective, where internal leakage is slowly applying the brakes, and forcing the pedal piston back.


Iirc, the rod to the master cylinder requires adjustment at installation, but that should not cause back-feed internally.


Make sure the rod does not compress the piston before the mc contacts the 'booster flange.

As long as your pedal is not pushing on your master cylinder then your brakes will not be applied if your hydroboost is working properly. Is your brake pedal return spring working properly. It is designed to keep the master cylinder rod from pushing on the piston. Sometimes rebuilt units are defective. I think I replaced three power steering pumps (from Parts Plus) within three or four months. So far Parts Plus has replaced my pump five (5) times!!!! I don't buy anymore parts from them!!!

sounds as if you either got a bad rebuilt master cylinder or you still got alot of air somewhere in your brake system. hydro boost unit sounds fine. ps.... ive had clogged lines do this also, check them first. the will let fluid pass but sometimes will not let it completly return.