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1997 ZJ Low Brake Pedal HELP!


 
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JeepersZJ
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Joined: 21 Nov 2007
Location: Western Massachusetts

PostPosted: Wed May 12, 2010 8:23 pm    Post subject: 1997 ZJ Low Brake Pedal HELP! Reply with quote

I am running out of ideas trying to find what is causing a super low brake pedal on my 97 4.0 ZJ Limited. So far I've tried everything I can think of might be causing this! This started after I flat towed it behind my motorhome, the e-brake partially stuck so the rear disc's overheated especially the left rear. I towed the ZJ over 200 miles and with a 8.3 Cummins pusher I dragged it all the way and never even felt it.

So far I've replaced the rear pads and the e-brake shoes, checked and bled the fronts plus I've also replaced the master cylinder and bled to entire system but I didn't get any air out. There are no leaks anywhere. The pedal goes to the floor but it does stop although I won't drive it that way. Any suggestions?
Thanks, Ken
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savasa
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Joined: 19 Mar 2009

PostPosted: Thu May 13, 2010 4:54 am    Post subject: Reply with quote

Jeepers,
Could it be that you've fried the rubber seals inside the calipers OR the rear brake hose causing some sort of internal collapse of the hose? It doesn't take a massive amount of heat to damage rubber components.
Peter
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JeepersZJ
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Joined: 21 Nov 2007
Location: Western Massachusetts

PostPosted: Thu May 13, 2010 7:02 am    Post subject: Reply with quote

Tnx for the reply Peter, I checked the rear calipers when I compressed the pistons to install new pads and there was no signs of leakage at all. If the seals were damaged wouldn't they leak?

Not sure if there would be any way of telling if the brake hoses are damaged. I hate this kind of problem! It's getting expensive to keep throwing parts at it hoping to find the problem!
Ken
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Orangeamc13
Got Rev Limiter?
Got Rev Limiter?


Joined: 20 Feb 2006
Location: East Springfield, Massachusetts - U.S.A.

PostPosted: Thu May 13, 2010 8:34 am    Post subject: Reply with quote

If you replaced the mc and then bled the entire system and didn't get any air out, I would think that there's still air in there. If the rubber lines are weak, they will expand while braking causing the pedal to feel lower. You might not be able to tell if the hoses are bad by looking at them.
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JeepersZJ
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Joined: 21 Nov 2007
Location: Western Massachusetts

PostPosted: Thu May 13, 2010 7:19 pm    Post subject: Reply with quote

I think your right on the hoses, they can do some pretty strange things when they age and unless one pops it's a guessing game. I wonder if enough heat built up from the e-brake hanging to damage the outer hoses going to the calipers? Also my wife just reminded me that this didn't start immediately after the e-brake hung but actually some time after that. When I bled the rear calipers the fluid looked real crappy so I kept bleeding til I got clean brake fluid but still no air.
furious
I bench bled the new MC then re-bled the entire after installing it but again no air. The pedal drops to the stops when the motors running bit it don't feel like air and it don't come up when pumped. The pedal is good when the motor is off.

Is there anything in the anti-lock system that could cause a low pedal like this? I don't know shit about anti-lock systems and I don't have extra $$ to keep throwing parts at it hoping to solve this!
Thanks, Ken
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Orangeamc13
Got Rev Limiter?
Got Rev Limiter?


Joined: 20 Feb 2006
Location: East Springfield, Massachusetts - U.S.A.

PostPosted: Fri May 14, 2010 7:50 am    Post subject: Reply with quote

I'm not sure about the ABS. I disconnected mine a long time ago.
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kaos
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Joined: 10 Jan 2006
Location: Iceland

PostPosted: Fri May 14, 2010 12:41 pm    Post subject: Reply with quote

Not sure, but I think ABS failure is a possibility, if not exactly likely. The mention of it has, however, reminded me; how did you bleed your brakes. ABS systems require a special procedure to exercise the ABS pump. According to the service manual to my '93 ZJ, this is done by a special program in the DRB code reader/service tool, but this may have changed in your model (for one thing, the DRB tool no longer applies to OBDII vehicles). I have, however, managed to bleed the ABS pump without a service tool by driving (very slowly and carefully) to a lightly trafficed stretch of gravel road, and there, hitting the brakes sharply enough to cause the ABS to activate. The ABS pump has a direct return line to the brake fluid reservoir, and will therefore "self-bleed" when it operates; no need for bleeding nipples. You may need to repeat this several times, and you may need to finish off by conventional bleeding to get rid of any air bubbles in the rest of the plumbing.

--
Best regards,
Kári.
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JeepersZJ
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Joined: 21 Nov 2007
Location: Western Massachusetts

PostPosted: Sun May 16, 2010 5:45 pm    Post subject: Reply with quote

I haven't had the time to try anything else but it sure sounds like the ABS is the culprit! Even the Haynes manual says a special tool is needed to properly bleed the system.

I think Orange got the right idea, get rid of the POS ABS! How hard was it to eliminate it? Just take the ABS motor right out of line and bleed as a normal non-abs break system? Any pointers Orange?
Thanks, Ken
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JeepersZJ
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Joined: 21 Nov 2007
Location: Western Massachusetts

PostPosted: Sun May 23, 2010 5:43 pm    Post subject: 1997 ZJ Low Brake Pedal - UPDATE Reply with quote

Just returned from an RV Rally in which I was a vendor. I ran out of time trying to fix the ZJ's low brake issue and pulled it behind my coach anyway. I figured that I would basically use it as a 4x4 "trailer" as I needed room for supplies.
I flat towed it a short trip to northern Massachusetts but when we got there and unhooked the Jeep something weird happened!
I NOW HAD A GOOD BRAKE PEDAL!
It still wasn't 100% but at least now I could drive it without "cleaning my shorts" every time I had to stop!
The ABS light is still on (it did that before occasionally) but the pedal isn't on the floor now Cool
Didn't do anything since bleeding them or even try to activate the anti-locks! I shouldn't look a gift horse in the mouth I guess!
Don't you just hate it when it's fixed and you don't know why!
Ken
thanks
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