Yesterday I replaced my front brake pads. After pumping the brake pedal a couple of times to reset the calipers I pressed down pedel and held it and it sank to the floor slowly. I repeated this several times and the problem continued. I know this is a typical symptom of a failed master cylinder so I replaced it hoping that maybe when the calipers were compressed rust just got pushed up the brake line. The master cylinder was bench bleed first then I followed the bleeding procedure in the service manual. The new master cylinder didn't help. With the engine off the brake pedal is hard and it doesn't sink but when the truck is started and the power assist kicks in the pedal slowly sinks to the floor when holding pressure of it. I checked for leaks and none were found any help you guys could give me would be greatly appreciated.

PS the truck is a 94 2500 4x4 with only rear abs

 

UH did you bleed all the brakes at each wheel? you need to have some one under there and crack each of the bleeders while the engine is running and you stepping on the pedal to get the air out.

 

UH yes. All componants were bleed according to service manual. But the problem started when the new brake pads were installed which doesn't make sense. Has any body else had this problem before?

 

I had this worry on my 96, after installing pads, but I just kept pumping the pedal, a little at a time, and it firmed up. I thought I had a bad master cylinder also, but the brakes are all good now.

Chris