87 Cherokee, been giving me some braking issues lately. All started a month ago when i went to stop and the pedal went to the floor, but i was able to pump it back up. I look under the vehicle, and see i have sprung a leak in my rear brake line. I figure this is the issue, it made it home. So new lines go in, aswell as wheel cyl.'s and shoes etc. Day later, pedal sinks to the floor again. seems to do it when you havent used the breaks for a while, and you can always pump it back up when it does fade away. Most of the time, it works no problem. Also, the pedal would sink while you held it at a stop sign for instance. So, i figure it must be the master cylinder. I replaced that, bled it properly, aswell as the whole system and it still does it. No leaks whatsoever. Any input on what to check next?

 

Brake booster would be the next place I would look.

 

Bad booster will cause high hard pedal. If you hold pressure on pedal does it hold or slowly crepe down . New dont guarantee good any more.

 

Pedal will hold if the pressure is there to begin with. 90% of the time it works fine, but every once in a while you will go to use the brakes and you will have to pump 2 or 3 times to bring it back. Symptoms havent changed throughout this process so i dont suspect the new master cyl. being bad, although if anyone has input on that i wouldnt rule anything out at this point.

 

No leaks some thing by passing letting pressure leak back.

 

what would be your first suspect?

 

Bad master. Even thought its rebuilt it can by pass internally. That's only part in brake system that applies pressure every thing else will leak.

 

Ah, thank you.