Random Brake Problem

[XJHummerRescue]

'89 Cherokee, 4.0, aw4

Starting yesterday, at seemingly random times, my brake pedal has no resistance, and will drop to the floor... It still brakes just fine, it just takes a few more inches of brake pedal travel, and I really dont like not knowing when my brakes are going to kick in. Is this a sign my master cylinder is going out? Booster seems to be air tight (according to the test in my Haynes manual) so I do not believe it is that.

Thanks,
Jeff

[CanMan]

I would start off with a MC. How many miles are on your rig?

[XJHummerRescue]

It has 157k miles on it. Most of the brake system (except pads, shoes, and 1 hose) are original.

[Matthew Currie]

Classic master cylinder failure.

Bad booster would not cause a sinking pedal.

[XJHummerRescue]

I replaced the MC yesterday and the problem is still there. I did bench bleed it, and everything is hooked up right. I checked again and still do not see brake fluid leaking from anywhere.

Any suggestions on where to look next?

Thanks
Jeff

[XJHummerRescue]

Just replaced the extremely worn rear shoes, still no change in the odd pedal travel dilemma. Tomorrow I am going to bleed the entire system, maybe there's too much moisture in the old fluid in the lines, unless someone has some input :).

Thanks,
Jeff

[Rick Anderson]

Well bleed the lines until there is all fresh fluid in the system. I do that close to once a year for all my vehicles, I've had original brakes on 230k mile vehicles that worked perfectly, only pad/shoe changes and new rotors.

Rear Wheel Cylinders are a common leaker, that could leak down the Reservour and soon as you suck air, 1 or the 2 stages goes limp. Plus if its a minor leak, it will usually self bleed itself, so if you add fluid, the pedal goes back to normal. Perhaps fluid sloshing as the vehicle moves uncovers and recovers.

Maybe a Rear Wheel Cylinder with an intermittent leak, it extends to a certain point and looses pressure.

Eitherway, you re-did the rear shoes, did you notice any fluid on the Wheel Cylinders?

How is the fluid level in the reservour as this happens? If your losing fluid, its a leak, fluid level stays the same, I'd guess a MC blown seal, but you just replaced that.

And last, brake leaks can be hard to spot sometimes, I looked for one on my Mini-Van for months, never spotted it until I had someone pump the brakes while I looked them over, then I noticed the fresh stream of fluid running down a caliper as the brakes were pumped. Same spot I looked over several times before, didn't notice it until I saw the fluid leaking down the side in action.

[XJHummerRescue]

The rear wheel cylinders had no fluid on them... in fact, they still had some mud on them from a wheeling trip a few months ago.
When I replaced the MC, the original one was leaking past the seal, because as soon as I loosened the 2 nuts, fluid started coming from behind the piston.
I have been checking the level on the MC daily, and it is not going down at all, unless it's going REALLY slow.
I will look for leaks with someone pumping right before I bleed them... no sense in bleeding them if I have to make a repair and bleed them again is there? :)

Thanks for the help,
Jeff

[anony91xj]

Do you have ABS? Weren't there wierd problems and a lifetime recall or warranty on the Renix ABS systems?

[RandyD71]

You need to bleed the system better. Make sure that you follow the correct sequence. Start at the master on the truck with the line closest to the booster. Move to the front line after that. Then you want to go RR, LR, RF, LF and bleed each wheel until you get a clean clear stream of fluid for atleast 2 times. If there is resistance now but still a low pedal make sure your rear brakes are properly adjusted as this will give a low pedal. If that is fine check to see if the rod coming through the power booster is adjustable. If so, you may need to lengthen it a little bit at a time to get the correct pedal height due to production variances between the master cylinders.

[XJHummerRescue]

Nope, no ABS.

I bled the lines at the master when I installed, and quite a few times too, but I will do it again before I start to bleed them after work. I have plenty of brake fluid :). I adjusted the rears last night after I did the shoes, and a re-adjustment will probably have to happen, so I'll do that after I bleed the system.

[woodyjeep]

speed bleeders will make it much easier to bleed ;) I have speed bleeders all around and it is nice

[XJHummerRescue]

Alrighty... Went to bleed system at the lines at the master cylinder and noticed my new one was leaking by the piston and pushing fluid out back by the booster, so I swapped it out again for another new one. New one bench bled, installed, bled lines at master, bled lines at wheels (RR,LR,RF,LF), checked for leaks on all brake lines along the whole lengths and at master cylinder again (making sure I didnt get another bad one), and then test drove.

The problem is still there! Went to the gas station on my test drive, and pulling up to the pump, brake pedal dropped to floor, and my E-Brake light came on. Went back off with another press of the brake.

I believe this is telling me (as well as the crud buildup in the bottom of the old master cylinder) that I have a sticking proportioning valve.

Anyone have experience with this? Input is appreciated.

Jeff

[woodyjeep]

Alrighty... Went to bleed system at the lines at the master cylinder and noticed my new one was leaking by the piston and pushing fluid out back by the booster, so I swapped it out again for another new one. New one bench bled, installed, bled lines at master, bled lines at wheels (RR,LR,RF,LF), checked for leaks on all brake lines along the whole lengths and at master cylinder again (making sure I didnt get another bad one), and then test drove.

The problem is still there! Went to the gas station on my test drive, and pulling up to the pump, brake pedal dropped to floor, and my E-Brake light came on. Went back off with another press of the brake.

I believe this is telling me (as well as the crud buildup in the bottom of the old master cylinder) that I have a sticking proportioning valve.

Anyone have experience with this? Input is appreciated.

Jeff

it's not a hard or expensive fix, just replace it and know for sure

[CanMan]

You may be correct on the Prop. valve. The symptoms you still describe would lead me to believe it is the MC, but I wouldn't be too hard pressed to say it may be the Prop. valve.

[Rick Anderson]

I'm a little skeptical, if the proportioning valve was leaking and losing fluid, then yea, I could see it being the cause. But you've said the fluid level is staying the same.

The proportioning valve/combination valve, does two things. It reduces pressure to the rear brakes and it has a piston/switch arrangement between the two stages of the brake system, so if there is a big pressure difference between the 2 stages it will move from the pressure difference and throw a switch to light the e-brake light.

The pressure reducer could block or do no reduction at all; eitherway the pedal would still feel the same and the rear brakes would be locking up or not braking at all.

The pressure difference switch, a properly working MC would have equal pressure on both stages, so no matter how blown seals were on the pressure difference switch the pressure would be the same on both sides of it.

That e-brake light is only going to come when there is a big pressure difference between the 2 brake stages. And the brake is only going to drop to the floor if there is a pressure drop. The only thing I can think that could cause boht;

*A Brake Leak (but your not losing fluid from the reservour)
*Blown Seals in Master Cylinder (your on your 3rd MC, that doesn't make sense either)
*Somewhere in the brake system, a huge expansion is being allowed without much resistance.

If your rear drum brakes were all messed up, they could be allowing one of the pistons in the wheel cylinders to move out really far and cause a pressure drop? Maybe a caliper has a piston being force back, so that it takes a full pedal stroke without building pressure? A hose is ballooning?

[XJHummerRescue]

The rear brake hose is new, got one for a '95 YJ when I put in my lift, but the front ones are still original... so maybe one(or both) of the front ones could be ballooning. I really doubt with brand new shoes in the rear that either of the pistons could extend far enough to cause the pedal to drop like it does, but the piston in the caliper is plausible I think. Any way to check that?

Jeff

[Rick Anderson]

I've seen bent up rear shoes that let the pistons in the rear wheel cylinders extend way to far and cause a soft pedal. But, yea, brand new shoes, as long as the hardware and the pins and backing plate were in half decent condition, I can't imagine how the rear drums could still be the problem.

Hoses ballooning, enough to make the brake light go off and the pedal drop to the floor? I was probably a little presumptious in that suggestion, I'd think the hose would have to balloon so bad to do that, it would have had to burst long ago.

Caliper, try pushing the calipers in the direction of the piston, you shouldn't be able to push in that piston by hand, you need a clamp or lever, like a big screwdriver, to get it to retract. If something is driving that caliper back while your driving, the piston is pushed in, there forms a big gap between pads and caliper, then the next brake pedal push, no pressure until the pedal strokes enough to push the piston back out to take up the gap. Never heard of happening before, but that is the only thing I can think of that could cause you to loose brake pressure without loosing fluid, and is not a bad MC. Once the piston is fully extended again and the caliper all snugged up against the pads, the brake should act normally until the piston is forced back in again.

Again, a lot can be learned by having a helper pump the brake while you observe the brakes at each wheel.

The proportioning/combination valve, I'm far from some brake guru so take my advice with a grain of salt, but from how understand how that part works, I just can't see how it would cause the brake pedal to drop to floor or the brake light to go off, unless it was leaking.

[XJHummerRescue]

Well, I did check the front hoses, and they are definately not ballooning. I went over every inch of brake line again, and there are no visible leaks (brake fluid would definately be visible on the light brown mud covering almost every inch of the underbody and almost everything under the hood :)) I will check the calipers, but I dont see how anything could force the piston back in.. but I have to check, im almost out of options here :explosion. What symptoms would the brakes show if the vacuum line to the booster had a leak in it? Same as a wearing/failed booster, or different? I would just disconnect it and try, but it's pretty stuck on there and I dont want to make a leak if I can help it :).

Jeff

Edit: Forgot to mention, I am noticing that EVERY SINGLE time I pull into my parking spot at work, the pedal drops, as well as my driveway. It seems like it happens more at low speed and rpm. I dont know if this could be related or coincidental, but it may be important.

[Rick Anderson]

A vacuum leak to the brake booster would give you less brake boost, the pedal would be harder to push down.

The Brake Booster only helps you push the brake pedal, if its bad, even in a way to make it too easy to push the pedal to the floor, then a good brake system would react just like you had slammed the pedal to the floor, it would lock up all the brakes. I got the impression from posts that the brakes don't change when the pedal drops to the floor, that can only be a pressure drop in the hydrualics of the brakes and definitely if you getting a brake light.

[XJHummerRescue]

I was just throwing the vacuum line out as a suggestion, just want to fix this problem. I really do not like not knowing where my brakes are going to actually brake. I am going to check the calipers/pistons and maybe bleed my brakes again just to be thorough, and this time with the engine on. Maybe I have some air still trapped somewhere.

Jeff

[XJING]

OK I hate to... but have to ask...... how are you bleeding your brakes?

I remember a while back evrybody tried to help a guy with a brake problem and found out after many pages of attempted answers he wasn't bleeding his brakes correctly. No flames please, you seem to have checked everything logical in the brake system. I am leaning to a faulty wheel bleeder or air being left in the system by improper bleeding.

[XJHummerRescue]

I bleed my brakes by first loosening the bleeder valve, then snugging it back up, then slipping my 2 ft. length of clear vinyl tubing over the valve (which goes to a 20 fluid oz. bottle about 1/5 full of brake fluid), having my assistant pump the brakes, then hold, open the valve, close valve, tell assistant to let off, repeat (from pump onwards). Then move to the next wheel after the fluid coming out is clear and no more bubble of air is coming out, checking MC fluid level frequently.

Edit: Clear vinyl tubing is 5/16" OD 3/16" ID... smallest ID tubing I could get to fit over the valves.

[XJING]

Once again sorry for even asking. You're problem is very unique thats why I had to ask, seems like maybe speed bleeders might be the answer as you might be getting a bit of air back through your current ones. Its a long shot, and a real long one at that but with new bleeders you have now cancelled even that out. I dont know what else it could be.... Good Luck

[XJHummerRescue]

Do not apologize, when it comes to something as important as brakes, I like to have my work double checked as a safety measure anyways. Just in case I have a brain fart or something. Never hurts to make sure I'm using the right method. I might go ahead and put on some speed bleeders, just so I wont have to have help to bleed them anyways :).

Jeff

[Blkxjkrawler]

When you replaced the rear shoes did you A) have the drums turned or measured and verify that they are within wear specs, and B) make sure that you have the primary and secondary shoes in the correct position? I have seen both drums that were out of spec, and shoes that were installed backwards cause just this type of concern.

[XJHummerRescue]

I did make sure that the shoes were installed in the proper position, but I did not have the drums turned nor measured. I didnt even think of it. The shoes that came off were worn uniformly per side(drivers side was worn more than pass. side though), and the diameter of the drum measured exactly 10" with my tape measure (even though I know that a tape measure wont be an exact measurement). I will look into the drums being measured or turned, or maybe just buy some new ones :).

Jeff

[Johnny V]

Look at your front calipers...I had huge problems with the brake pedal going to the floor. Turned out one of the problems was on install, an inner caliper fell off it's rail/slider and got hung up...I wasn't aware of it until I took the whole system apart and started from the beginning.

A belated big :kissyou: thank you to Rick Anderson for sticking with me through my brake trials and tribulations a few months ago!

[XJHummerRescue]

I think I will do that... I'll take apart and inspect the entire front disc brake system to make sure all is in order. I put new pads on about 3 weeks ago, and the problem showed up about 5 days ago, but something could have possibly shifted. Thanks for the suggestion.

Jeff

[XJHummerRescue]

I just went for a drive, and the pedal dropped all the way to the floor again, and the brake light came on again, and there was a big clunk from the right front wheel. I think I will look there first for my brake problem, maybe a broken/dislodged pad or a messed up caliper.

Jeff

[Johnny V]

Turned out one of the problems was on install, an inner caliper fell off it's rail/slider and got hung up...

Correction...I meant inner pad not "inner caliper".

XJHummerRescue,

Looks like you are on to something!

[XJHummerRescue]

Checked the right front caliper and pads, everything seemed in order... no leakage around the piston, and everything was where it's supposed to be. The pins (whatever you call them, what the caliper slides on) were a little stuck, but I greased them up and put it all back together. Havent taken it for a drive, but I dont think I fixed anything.

[XJHummerRescue]

Got married on the 8th, so I really havent had any time to check anything, but now I'm back to trying to fix my brakes. I still need to inspect the front drivers side brakes, and I am going to re-inspect the rear wheel cylinders for leaks.

Jeff

[XJHummerRescue]

Just checked drivers side pads and caliper... again everything is in order. Will try to check rear cylinders today, if the heat doesnt get to me too bad.

[crazyray]

hey had a similiar problem, its the front hubs going south. they allow rotor to push pad back and then next brake application it has to push out pad. to check take big heel bar and push pads away from rotor then remount wheel on that position and check for side play. hope this helps you but hurry this will continue to get worse

[Xj'sR'Creamy]

Congrats on the marriage. I just read this thread and am pretty confused myself as to what could be the solution to your problem. I wouldn't hesitate to check out those hubs as crazyray suggested...sometimes what you're looking for isn't where you'd expect it to be.

Sean

Good Luck...with the brakes...and the wife ;)

[XJHummerRescue]

Thank you :). The drivers side hub is only around 5 months old, as it was going bad. I checked the pass. side one then, but lots can change in 5 months. Add another thing to my to check list ;). Why do I always have to get the complicated problems? Hehe...

Jeff

[crazyray]

did you find the problem would really like to know outcome

[XJHummerRescue]

Not yet, I had to divert my attention to a window broken by someone who felt like it needed to be broken... One of the big side windows (its a 2 door) and I've been getting quotes to get it replaced. It was parked in my driveway too, mid-afternoon, and I was sitting in my living room, only about 20 feet away. Windows were down and doors unlocked too... Makes me mad. I dont even live in a bad neighborhood.

[davehoose]

sorry to hijack, but have a similar problem but may not be related. A couple weeks ago i found a plug next the master cylinder that wasn't plugged in so i plugged it in to see what happened. nothing, at first. i don't know if it's related but i have less and less brakes, need to push harder and i here a hissing sound inside by the pedal constantly when i hold the brake pedal in. i unplugged the wire but no change. really concerned about the hissing sound by the brake pedal but can't seem to see where it's coming from. any clues?
89 xj 4.0 aw4 98000 miles.

[Lighterknot]

any update? I just had a similar thing happen to me today...pedal went to the floor, heard a clunk from up front and the e-brake light came on. only difference is, I haven't done any maintenance to my brakes in about 8 months.

[Lighterknot]

well I checked my brake fluid, and it was really low...about the half way point on the reservoir. I filled it up and pumped the breaks a few time and then once really hard and the e-brake light went off. still not sure if my breaks work and don't see how that could have fixed anything...I plan on bleeding my brakes and checking for leaks before driving it.

[XJHummerRescue]

I still havent found the problem, and I recently had a family emergency, so I have been busy with everything except fixing my brakes. I've been driving my mother in laws Jeep to work and back, and just had the quarter window fixed today. Now I need to get this fixed. There are a couple things I still need to check. I'm getting pretty fed up with them :explosion , if I dont get it fixed soon, Im just going to take it to a shop. I will give updates if I find anything else out. Maybe someone else down the line will have a brake gremlin ;).

[XJHummerRescue]

Okay, I took it to a local mechanic and he found out the problem for me. My nearly brand new front drivers side hub assembly is already toast, as well as I had a barely noticable small leak in the back side of the proportioning valve. I never saw the leak, but I just checked, and the front drivers side hub sure is gone. Surprised it hasnt fallen apart already :explosion.

Thanks again for everyones help with my months long chase of my brake gremlin.

Jeff

[XJHummerRescue]

Sorry for dragging up such an old topic here, but I never actually posted the real culprit in the end!

When I had previously replaced the drivers side wheel hub, I forgot to put locktite on the bottom bolt, and it had slipped out sometime while driving. That allowed the movement to push the rotor around and screw with my brakes. Oops.

[andrewsnyder]

Sounds like you had a brain fart!! lol I'm glad it got fixed and no one got hurt!

[in2fords]

Ive been fighting the same problem, theres something else to check.

[Brett M]

I've been having the same problem off and on as well. Might be time for new hubs!