Hi guys,

I've got an 89 Cherokee Limited with the 4.0. The brakes are less than perfect and i have bled them twice with no improvement. Tonight i was driving with the radio off and i could hear a hissing noise under the dash with the brake pedal 3/4 the way down. if i let up or push them to the floor the hissing stops. It only hisses around 3/4 the way down. Could it be a leaking booster? The pedal doesn't seem hard to push but i know the brakes could/should be better. What do you think.

 

most likely the brake booster leaking internally. Mine is doing the same thing and i plan to swap it out in the near future.

 

Agreed

 

Hey guys mine does the exact same thing. Is there a way to test the booster to make sure its faulty?

 

Disconnect and plug the vacuum line going to the brake booster. If the hiss stops then your booster is faulty. (if you dont plug the line you will have a crazy high idle speed)

WARNING! this will disable the power assist on your brakes so be aware that you will need to press on the pedal MUCH harder to stop!

 

My pedal is doing the same thing. Parked idle is around 1200rpm but drops to 700 when brake depressed. Bad booster?