Bad Brakes

I know this has been beaten to death, but I thought I'd post my brake problems here and what I'm doing to resolve them. If you are having problems with your brakes/booster/master cylinder, I hope this helps.

First of all, I have an 87 XJ almost stock (completely stock in the brakes department). When I bought it, the brakes were spongy and the brake light was lit. When depressing the brake pedal, I would hear a constant shhhhhhhhhhh sound from under the dash.

The first thing I did was replace the brakes. Fronts are very easy to do and I believe that process is covered in other posts on this site. There are two different versions of pads for the Cherokees, so take your old pads in once you get them off and make sure everything matches from old to new. I tried to be prepared and picked up a set of pads ahead of time only to find out I had the wrong ones. These ended up costing just over $30 for both sides. The old pads were completely gone and the rivets that hold the pad material on had dug into the rotor about 1/8". I had to pick up new rotors which ran about another $35 for both sides. Both wheels took under two hours.

The rear drum shoes aren't too bad if you've done any break work before. I highly recommend getting a retainer spring tool from the auto parts store (they're about $5 and relieve about $50 worth of frustration). New brake shoes ran about $30 for both wheels. Both wheels took about three hours (including cleaning everything up with a wire brush). Make sure you lube the brake adjuster assembly with a bit of grease while you're swapping all the parts around. The Haynes manual was very handy to have on hand for the rear brakes.

After getting everything adjusted and bled, the Jeep stopped much better and the light went out occasionally.

I could pump up the brakes, hit them hard and come to a very quick stop. I still heard the shhhhhhhhhh from under the dash and the system would still lose pressure causing the brake light to come back on occasionally, but I could pump up the system and the light would go off.

I was afraid that I was losing fluid from one of the calipers (front) or wheel cylinders (rear), but after careful inspection, I don't believe that to be the case. Also, the fluid level in my master cylinder is not dropping.

I did notice that with the cover off of the master cylinder, brake fluid seems to escape from the piston when the brake pedal is pressed. I'm not sure if this is normal, but I don't think it's supposed to do that.

After a bit of research, I believe the shhhhhh from under the dash is a bad brake booster. With the brakes losing pressure and the fluid escaping the cylinder, I figured my master cylinder is bad as well.

I removed the old master cylinder and brake booster (I had to take off the window washer fluid reservoir to get to everything). I was expecting this to take quite a bit of time, but it only took about an hour and 15 minutes doing all of the work by myself. I just picked up a new booster and master cylinder (about $100) and will be installing it this weekend. I'll give an update after it's in.

If this doesn't do the trick, I think I'll move on to the proportioning valve, wheel cylinders and calipers.

I call these "all you gotta do..." jobs. I hope the booster is the final step for you.

It was your brake booster going bad.

Happened on my 88. Replaced and fixed the problem.

I'm having a similar problem, just without the sound...

My 93 XJ had a leaky master cylinder. The level got low and it sucked some air into the lines. I figured while I'm bleeding it, I should replace the master cylinder. I did that, and bled the brakes and they worked great for a couple weeks. But all of a sudden yesterday I lost pressure in my brakes. I can pump them and get pressure back which makes me think air somehow got into them again, so I checked my fluid level in my master and it's the same as when I replaced it a few weeks ago. So I'm quite sure I'm not leaking it out somewhere, but how would air get into the system without fluid leaving it through the same place?

It's -25 here and I don't want to spend hours laying under my jeep in the driveway with the cold and wind, but it is a necessity since I need it to get me to work (the garage is full of my summer toys) so any help or pointers are greatly appreciated if it saves me time outside

If you find your brakes are still not good enough for you, its an easy job to put a WJ master/booster into an early XJ, and will REALLY increase your brakes. I put one in my 87 with 35's and can lock up the tires now.

http://www.4x4wire.com/jeep/tech/brakes/xj_wjbrakes03/booster/

I got a WJ booster and master from a 2004 WJ with 40k miles for $60 shipped via www.car-parts.com, and spent about $30 on misc parts from the store. The entire job took me less than two hours to do.

Isn't there a vacuum switch under there for the cruise control? I would think a hissing would mean a vacuum leak near the brake pedal.

Isn't there a vacuum switch under there for the cruise control? I would think a hissing would mean a vacuum leak near the brake pedal.

Click to expand...

Maybe, but I don't have cruise. The sound is coming from the pedal area and only when the brakes are applied.

ert01 said:

I'm having a similar problem, just without the sound...

My 93 XJ had a leaky master cylinder. The level got low and it sucked some air into the lines. I figured while I'm bleeding it, I should replace the master cylinder. I did that, and bled the brakes and they worked great for a couple weeks. But all of a sudden yesterday I lost pressure in my brakes. I can pump them and get pressure back which makes me think air somehow got into them again, so I checked my fluid level in my master and it's the same as when I replaced it a few weeks ago. So I'm quite sure I'm not leaking it out somewhere, but how would air get into the system without fluid leaving it through the same place?

It's -25 here and I don't want to spend hours laying under my jeep in the driveway with the cold and wind, but it is a necessity since I need it to get me to work (the garage is full of my summer toys) so any help or pointers are greatly appreciated if it saves me time outside

Click to expand...

Make really sure you're not losing fluid somewhere hard to see, like a rear slave cylinder.

It's always possible you got a defective master cylinder, especially if the one you bought was rebuilt rather than new. I'd try one more bleed, just to make sure, but if the brakes go soft again without any fluid loss, I'd suspect that. While you're at it, try turning the engine on, so that the booster is boosting, and press slowly on the pedal, firmly but not too hard. If the pedal sinks slowly to the floor, there's either a leak somewhere (which should show somewhere)or a bad master cylinder.

UPDATE:

I installed the new master cylinder and booster last night. I wrangled two other folks into helping me (I would highly advise having someone hold the booster in place while you bolt it under the dash). It took about 45 minutes to get it in and hooked back up. It took about another two hours to bleed everything out. I finally finished the bleeding this morning.

No more weird noises and the brakes will throw you through the windshield!

NOTE - part of my problem was that the rear brakes had MUCH air in them. My brother bled these for me when I changed the back brakes and he failed to mention that he didn't get any fluid from them. The bleeders were so clogged with dirt that no fluid could pass. I cleaned them out by hand with a small drill bit, bled both sides and WOW!

Whole project cost just over $200 with all of the parts, fluid and tools. Not sure how much this would have cost in the shop, but I'm guessing it would be approaching $1000 (my brother-in-law had his master cylinder replaces in the shop last week and it cost $720-ish - that's with no pads, shoes, rotors, or booster!). So, I estimating that I saved enough money to go buy another XJ!

kd5dwy said:

Not sure how much this would have cost in the shop, but....

Click to expand...

No contest. You're way ahead.

Matthew Currie said:

Make really sure you're not losing fluid somewhere hard to see, like a rear slave cylinder.

It's always possible you got a defective master cylinder, especially if the one you bought was rebuilt rather than new. I'd try one more bleed, just to make sure, but if the brakes go soft again without any fluid loss, I'd suspect that. While you're at it, try turning the engine on, so that the booster is boosting, and press slowly on the pedal, firmly but not too hard. If the pedal sinks slowly to the floor, there's either a leak somewhere (which should show somewhere)or a bad master cylinder.

Click to expand...

I'll check for leaks more indepth, but the fluid level in the master hasn't dropped which is why I'm a bit confused, unless just a tad of oil left and some air got in then.

I still need to replace my brakelines though from when I did my lift, so I'll give it a thorough exam tonight when I'm putting the new lines in. Hopefully I'll get it figured out during that process.

ert01, doesn't take much of a leak to let air into the system. You may not observe any change in fluid level and still have "weeping" at one or more connections. Wipe each connection clean and dry, pump brakes and hold pressure for 10 sec or so, then check very closely for wetness; don't need to see drips for there to be a problem.

I didn't have time to replace the brakelines, but I did quickly bleed the system and after 10 minutes of work it was feeling good again. I still didn't notice any leaks though...

I'm quite new to all this stuff so I'm learning as I go. Feel free to correct me
here, but is it possible that there's a leak inside one of my rear dums? When I bled the fronts, no air came out, but the back right had air that came out but I still didn't see evidence of a leak. Are there seals in there that can go bad?

is it possible that there's a leak inside one of my rear dums?

Click to expand...

Yes.

Are there seals in there that can go bad?

Click to expand...

The fluid goes to a wheel cylinder under the drum. If the wheel cylinder is leaking, it's not good. This can cause the brake to stop working (the leaking fluid lubricates the brake) and can cause the shoe material to glaze.

These wheel cylinders tdo wear out over time (as with any moving part). The piston and sleeve wear down allowing fluid to pass between them.

A quick check looks like you could replace both wheel cylinders for about $20 plus some time (in the neighborhood of three hours). You'll have to disassemble the entire rear brake to get them out and re-bleed the system once they go in. Having a Haynes manual handy wouldn't be a bad idea in case you forget how something goes together. Make sure you do one side at a time for the same reason (you can always use the other side as a reference).

Brakes are just one of those things where you don't want to have doubts. I would rahter not be able to go than not be able to stop!

the back right had air that came out

Click to expand...

Are you sure they were bled completely to begin with? Once you bleed them out, try re-bleeding in a few days. If you continuously get air into the line you have a problem. If you stop seeing air after a few bleeding sessions, you never got all of the air out.

I have a haynes already, and it's been quite a handy pal so far. As far as bleeding them goes, I'm quite confident they were completely bled the first time. I took it into a shop and they power bled the brakes. They felt amazing after I got it out of the shop and slowly over the past weeks, they got worse again until I had to rebleed them last night. I know I didn't get it done completely lastnight cause they don't feel as good as when the shop did it, but it's good enough to lock up all 4 if I hit them at normal driving speeds (70km/h).

I will be checking them over the next week here and re-bleeding them if necessary because I don't have time to fix it until next weekend now.