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View Full Version : Brake Problem.. any help appreciated!


thewooddogg
02-22-2005, 11:27 AM
Hello fellow AZ Jeep'rs!

I've been a AZVJC lurker for a while, always reading stuff and looking for stuff, waiting for the time that I have a little extra money to get a lift and have some fun with you guys. Well, that never seems to happen, but my 88 Jeep Cherokee keeps getting older while the time goes by.

Recently, I've had a problem with spongy brakes, a "hissing" brake booster, and a leaky master cylinder. So, I started a week ago by going down to the autozone nearby (yeah I know they don't have the greatest parts but I can't afford expensive ones for my daily driver), and picked up a master cylinder, brake booster, and a bunch of brake fluid.

I installed it exactly as the instructions and my Haynes book said too. I cycled in the new brake fluid to completely replace the nasty black old stuff. The new brake booster works outstanding! The new master I have some concern about. My brake pedal travels too far! I have very responsive braking at low speeds, but if I'm driving above 30 or so my brake pedal goes all the way down and the brakes never lock, although it does stop eventually, but not safe enough in my opinion.

I started by thinking it was my master cylinder not being bench bled well enough, so with my freshly purchased bench vice I removed and bench bled it, reinstalled it, bleed the brakes again, and tested. I did this twice, by the book both times. Second, I messed around quite a bit trying to get the booster push rod perfect, I tried 3 different methods of adjusting it correctly. (although, I'm still not satisfied that I got this part correct).

So then, I figured I'd start with the hard part first, the rear brakes. I replaced the drums (autozone showed me one of them was cracked in quite a few spots), shoes, all the springs and stuff (except for the self adjusting stuff), and both wheel cylinders (one was leaky, and they were cheap to replace).

The pedal still goes to the floor. Still very responsive at low speeds, but not enough braking power at higher speeds.

So, the only items left to replace: Comination valve, front calipers, front rotors(if they can't be turned, front pads, and brake hoses.

Anyone have any advice for me?

I'm at a loss... I'm going to try and adjust the booster rod again tonight and re-bench bleed the master cylinder. If that doesn't work, I'm going to replace the front brakes. If that doesn't work, I'll replace the brake lines, and then call the stealership to see how much a new combination valve costs. After all that, I will have essentially replaced all the brake parts except for the metal lines... If it doesn't brake well after that, I'll drive it off a cliff or something... jk

jeep108
02-22-2005, 11:44 AM
It sounds like you bled the master enough.Did you bleed the rest of the system?Sounds like you need to bleed the rest of the system.

thewooddogg
02-22-2005, 12:54 PM
Thanks for replying Ken!

I appreciate your time to suggest an idea. Unfortunately, I did bleed the brakes anytime I disconnected a brake line. I used the method out of my Haynes book which seems to be the most thorough and standard method.
I can tell you, that my wife is getting pretty sick of pushing the brake pedal for me! :P

Anyone know a smart way to adjust the push rod on the booster?

I don't know if this is possible, but I keep thinking that maybe the master is sucking up air from the lines when trying to bleed it. What I mean is, when I remove the master, the 2 lines it was connected to are dripping a bit. Air probably gets in the lines, I bench bleed the master, then reconnect it, and start bleeding with the right rear... is it possible the master is getting air from the lines at that point?? It makes sense, but it doesn't at the same time... if I'm right, then how would I ever bleed the lines right? hmmmm

richard
02-22-2005, 07:25 PM
check the vacume line going to the boster for cracks :confused:

rvisokey
02-25-2005, 04:03 PM
Start with the vac lines. Sounds like you may have a crack.

Also, during your bleeding you should check the level of fluid in the master C. It should never get below 1/2 full before you re-fill or you might suck air during the peddle pumping action of bleeding the brakes.

Make sure the person pumping never gets the 'peddle to the floor' while you are bleeding the line. If they hit the floor and you haven't closed the line it can suck air back in.

OlneyJeeps
02-25-2005, 07:01 PM
If you are hearing hissing when you press the brakes, it is entirely possible/probible you have a defective brake booster.

after the engine is turned off, the booster should still be holding vacum (pull elbow from booster and you should hear release of vacum)

if you were to suck on hose going into booster, it should develop vacum.

Alternate method of bleeding brakes: one at a time, open bleeder valve, connect piece of vacum hose to it with other end in a jar full enough with brake fluid that end is submerged. Pump brake pedal (slowly) 3-4 times. refill master. repeat 2-3 times per cylinder. Discard fluid emitted into jar (brake fluid acts a dedergent absorbing moisture; should be changed every 3-6 years to remove moisture from system)

where are you located (beer level is getting low in my fridge)?
as I have replacd over 2dozen masters and boosters, I dont think it would be much to fix
Steve (N central PHX)