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Brake Help!!

metalhead

NAXJA Forum User
Location
south carolina
I have visited this website many times, and it has helped me greatly just by reading various posts. I now have a condition that I think warrants a new thread. The background on my XJ is a '96 country with 180k with 9 in drums and ABS. I have had the jeep since I bought it used from a dealership in '99 with 56k. I can't recall when it started (some years ago), but I started noticing a decline in braking ability. Some time after this my ABS light came on. I assumed it was a sensor that went bad, and I didnt do anything to fix it becasue I hate ABS and it wasnt kicking in anymore. I dont htink this has anything to do with my problems, because it came on after the decline. I had the jeep on a lift and was trying to diagnose some other problems when i decided to put it in 4wH and slowly let the wheels turn. When i pressed the brakes as hard as i could, it took like 15 secs. to get the back wheels to stop, while the fronts locked up. I tried the handbrake, and it yielded the same results. This is when my troubles began. I took the drums off to find the adjusters all the way in. I greased them, adjusted them, and it would help for about a day, then I would have to readjust. I also tightened the handbrake cable. This process went on for some time. Then I went on a week long trip, came back and saw where a wheel cylinder was leaking. I replaced both, and since it started leaking while it was parked, there was no fluid on the shoes. Braking was still the same as it was. I just put up with it for a while. Then one day on the way to work, a yellow light changed to red quicker then expected, and I moderately applied the brakes. The pavement was a little damp from a very light rain we had, and I went half-way through the intersection with front brakes locked and losing no speed (I am sure this looked pretty funny to the other cars). I never did stop, just gassed on it and looked in the rearview mirror expecting to get pulled over. That was the last straw (or so I thought). I replaced the shoes, springs, adjusters and drums because they had a lip on them. The braking didnt get any better. Also, when you pull the handbrake, its really hard to pull, but it will not lock up the rear tires, even going at speed in wet grass!! I got really mad and adjusted the crap out of the shoes. All this succeded in doing was heating up the brakes and causing a horrible vibration after 15 miles or so. I had to let them back out. From there I got on this forum and found out about the combination valve. It seemed to be the perfect fix. Had to order one from the dealership, and wait 2 months for it to come in. It got here, installed it, and flushed the old brake fluid til clean brake fluid came out at all 4 corners. Bled it at the master cylinder as well. Still no change in braking ability. I was one step away from pulling my hair out, but decided it was a lost cause. I have been driving my jeep this way for probably about 2 months now when yesterday and today I started losing my brake pedal. If you are on a long, solid brake, like getting on an off ramp from the interstate, its fine. If you need to make a left turn or so at a red light, and you have to pull forward a little, stop, pull forward, stop, etc, then every time you press the pedal, it goes lower, then lower, then lower. All the way to the firewall (even though I havent let it reach that far yet). If you release the pedal fully and press again, then full pedal again. It holds when you apply the brake. It only does this if you press the brake and release, but not let the pedal come all the way back up before you press again. It has never done this before. You still have full braking ability (or I should say full front braking ability) at each increment, but i am scared its gonna get worse, or i am gonna get to the firewall and have no brakes. I checked the fluid level, and its not getting any lower. So as you can see from the length of this post(sorry), I have been dealing with this for a while and I am about fed up with it. Any help will be greatly appreciated, although I will be pretty mad if it is a simple fix that has caused me gray hair at age 24 :). And while I am at it, whenever I get gas, the pump cuts off every 23-46 cents. Takes me 15 min to fill up. I wanted to get some advice before I tackled that prob. I am thinking its either a vent tube clogged, or the fill hose has a crease in it. Let me know what you think so I only have to drop the tank once. Thanks in advance!!
 
Sounds like you are incrementally losing your master cylinder, and have already lost the rear system. The test you describe is indicative of a master going bad, the bleed down, ect. I am wondering if you are seeing any pressure at all in the rear, since you can adjust them up all the way but they still won't stop you.

The parking brake problem may be an entirely seperate issue, you can check for corrosion in the cables and sleeves, that is usually the issue, see if you can get some penetrating oil in there to loosen things up. You can access the most troublesome spot right underneath the rear passenger floor pan on the driver's side.

Gas problem ??? You'll have to look see on that one.
 
I would definetly consider the master cylinder. You may wish to have it checked professionally before you purchase/rebuild. I would hate to have you act on my advice and it not be the problem. It could be a portion of the ABS (I am not familiar with the Jeep ABS) not allowing pressure to the rear system.

No, all the parking brake does is mechanically move the brake shoes to engage the drum. The normal brake system does this hydraulically. All you are doing when you adjust them up is moving the shoes closer to the drum, thereby reducing the amount of a) travel necessary with the parking brake handle and b) travel necessary through the wheel cylinder, master cylinder and brake pedal.

After re-reading your post, I am beginning to wonder if you have the correct diameter rear drums.
 
I am pretty sure that I have the correct size. My memory has never been that good, but it seems like they come in 9 in and 10 in drums. I have always used the 9 in shoes, and when I went to buy the new drums, they accidentally gave me the wrong ones (the 10 in). I didnt notice it until I got home, but there is no way I could use the 10 in. The 10 inch were so thick and big I couldnt even bolt my stock wheel on. So i am pretty sure it is the right size.
 
Between the pedel-drop, and the substantial lack of braking power, I'd certainly be suspecting the master cylinder.

One thing that you've got to remember (and most people here seem to be forgetting!) is that the majority of braking is done by the FRONT wheels. Really, even if the rears were to stop working COMPLETELY, you'd probably only lose 20-25% of your ultimate braking ability.

Den
 
That is a good point. But what makes me think that they can work better is when they wont even stop the tires when the jeep is lifted. Do you think having little to no rear brakes is part of the master cylinder problem too, or just the sinking pedal?
 
Yes. The master cylinder is basically configured into two systems, front and rear, so if you lose one you have the other. And yes, the rear brakes should work to stop the wheels if on a lift. Most vehicles have a proportioning valve to distribute working pressure as DenLip said, around a 75-25 split. I have seen these go bad too, but you may have a master cylinder problem because of the bleed down you're experiencing. Multiple problems? Possible.
 
i just wanted to say that I replaced the master cylinder, and it solved the problem with the sinking pedal. Also, in testing afterwords, I found that while going 45 mph and slamming on the brakes, the fronts didn't lock up this time. Thats with bald tires on the front. Thats a defininte improvement and it may have even solved my dilemma. Still a little too early to jump to conclusions, but if def. helped. Thanks for all of the help!!
 
metalhead said:
i just wanted to say that I replaced the master cylinder, and it solved the problem with the sinking pedal. Also, in testing afterwords, I found that while going 45 mph and slamming on the brakes, the fronts didn't lock up this time. Thats with bald tires on the front. Thats a defininte improvement and it may have even solved my dilemma. Still a little too early to jump to conclusions, but if def. helped. Thanks for all of the help!!

Sounds as if you are "back in proportion". At least all your braking power is not going to the front. Bear in mind, the Cherokee braking system is not the strongest in the world. You have to lean on them pretty hard to even think about locking them up with good traction. Matter of fact, I cannot recall ever locking mine up on dry pavement.
 
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