zj rear disk brakes not working!!!

Ok, ive done some searching on zj rear disk brakes, and learned what all to get from the lists every one posted. I read some people changed the proportioning valve out, and some did not.

Well, friday i went to the pick and pull and got everything but the ebrake stuff and the proportioning valve to put on my 97 8.25.

None of the 7 zjs i saw had any of the ebrake stuff left on them or i would have gotten that too.

After installing, and bleading the brakes 3 times using up 2 of those big containers of fluid, i still have problems.

When you step on the brakes, the brake light comes on, and the peddle all but goes to the floor, if you let off and pump it one time, the light goes off, and you have pretty decent peddle, pump it again and great peddle, let off drive a block, and step on the brakes, and almost no peddle again.

I took it for a drive, and at 40 stomped the brakes just to make sure it was save to drive, and the fronts locked up solid right off, and i could feel the rears catch, but not as strong as i would have liked.

What am i missing here? Feels like im loosing pressure and i did not have this probem before the conversion. Do i have to have the zj proportioning valve to fix this problem?

Are you sure you got all the air out of the lines?

very sure, and we i double and triple checked all connections, and nothing is leaking, if you pump it about 4 times and hold, the peddle does not fade a bit.

We blead the brakes for around 3 hours this evening, kept thinking there was air in there somewhere, but there is not, we are sure.

You have the rear calipers on the proper sides, right? With the bleeder valves on the top?

Did you use the rotors and pads from the junkyard? If so, what condition are they in?

xjohnnyc said:

You have the rear calipers on the proper sides, right? With the bleeder valves on the top?

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Yes, i marked them when i took them off

EricsXJ said:

Did you use the rotors and pads from the junkyard? If so, what condition are they in?

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yes i used both the rotors and the pads from the junk yard, the pads looked new, and the rotors had just a bit of surface rust on them, so i took the grinder with a wire wheel to them, and they shined right up. Neither the rotors or the pads had any marks in them to say that they where bad or worn funny.

Ditto the response on the bleeder position.

If they are not both in the same position, you'll get a small bit of air trapped in one caliper that will cause all your symptoms. You'll not get it bled unless you take the caliper off, rotate it upside down, use it to clamp the rotor, bleed and then reattach to the caliper bracket.

I've had this happen with my Ford brakes and everything seems normal until you step on the pedal while moving and you realize you're not stopping.

Yeah, double check the bleeder position. Even though you marked them in the yard, they could have been installed wrong before. That might even be the reason that Jeep was in the yard.

You could also try gravity bleeding the system.

I have them both with the bleeders up

I there anything else?

Does your Jeep have ABS? I recently had my brakehose to the rear axle removed in search for a longer one. The original was installed when we ran out of time, the brakes bleeded and now I'm having the ABS pump kick into action everytime just before the vehicle comes to a stop. I've read the factory service manual and it seems the car need to be connected to a computer when you are bleeding the brakes. I think somehow the ABS pump can be activated during the bleeding process to make sure there is no air in that part of the system.

If you've bled them right, it must be pads/rotors or calipers.

Mine bolted right up and worked after the first time I bled them, I used junkyard calipers and they were all good.

I didn't even bother trying to get the junkyard rotors and pads, that's just silly. Why potentially save yourself $80 (what it cost for new rotors and pads) to get used rotors? It's dangerous and seems stupid.

The point of the mod is improved performance and reliability, right? Why cheap out on small, frequently replaced parts? You wouldn't rebuild a DS with junkyard u-joints, would you?

Anyways, remanufactured calipers are $30-50 a piece, start with pads and rotors, progress to calipers next if you have to. Worst comes to worst you got some cheap cores.

On my '97, I didn't end up needing to touch the prop. valve or anything else, so I really doubt it's something funky with your hydraulics.

Unless you ran the master cylinder dry sometime during 3 hours (seriously?) of bleeding your brakes.

have you tried removing the internals of the prop valve and testing the brakes then???

that shouldn't take long and is something else to test

Fred85 said:

have you tried removing the internals of the prop valve and testing the brakes then???

that shouldn't take long and is something else to test

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Not particularly safe and addresses a part of the vehicle that didn't have anything change...

Did you pump up the brakes 10-15 times before bleeding? And start with the passenger side rear (longest brake line first)?

To me it sounds like there is still air in there somewhere.

Did you fill the calipers and hoses before installing them (in effect priming them)?

If the above is all good, I'd say calipers are the next likely candidate. I could easily see pads and rotors being worthless, but not causing the problem you're talking about (having to pump up the brakes to get a good pedal).

I know from personal experience that this mod can be done to great results (on 31x10.50 M/Ts and my braking is better than stock was) on a '97 without touching the prop valve in any way whatsoever.

NighthawkXJ - sorry we missed you monday. It was a good time. I am having a totally different problem with my zj disk brake conversion. Hope you can fiqure yours out.

Have you had any luck fixing the problem yet? I am in the process of getting the parts for the conversion on my '97. Also, where did you find a pick-n-pull around here? I live in Ellsworth and would like to find a ZJ prop valve.

I think the problem with my disc brakes have been fixed, i back blead the brakes in the rear, and they are working now.

I think the continued problems that i have are either a master cylender, or a power booster. Before starting the jeep, i push on the brakes, and all are locked and peddle is good. Then i start the jeep, and the peddle goes around half way to the floor. I have done some reading on ::, and according to other peoples problems, it has been said that it is the brake booster.

The light is no longer on, and only comes on if you panic stop hard. Normal day to day driving, besides the peddle not being where i want it to be, the brakes work great.

Has any one else ever had a problem with the power booster? Or was the information i read correct? I would rather be told im wrong before spending 100 on a new power booster and not have the problem fixed.



As for where i got the stuff, i went to a pick and pull in Kansas City, MO right off I435. I did see anouther zj at the pick and pull in Kansas city, KS later that day that was complete at the Upull it on 12th street right off of Kansas St. If you decide to go up there, let me know a bit in advance, i know alot of us from salina did not bring enough money with us last time we went, and saw alot more we wanted. I have a little trailer, and we usually just take the jeep and make a day of it.

I know you said you bled your brakes, but did you happen to bleed the MC? Maybe try bench bleeding the MC before replacing the booster? I don't know a huge amount about brake systems, but I know from experience that the MC traps a ton of air and can cause problems.

53guy said:

I know you said you bled your brakes, but did you happen to bleed the MC? Maybe try bench bleeding the MC before replacing the booster? I don't know a huge amount about brake systems, but I know from experience that the MC traps a ton of air and can cause problems.

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That's what I was thinking too. If you let the reservoir run out of fluid at any time you're going to need to bench bleed it.

I have not let the mc run dry, but that is one thing i have not tried so i will give that a try.

I back blead all the brakes all the way around to get what i have now. I just wish there was a way that i could back bleed the whole rear and then the whole front at the same time, but hey, i only have 2 arms, and they are only so long.

I have great stopping power, and i love that, lots better than drums, just cant seem to get the peddle back where i want it.