HCH

My first post! I hope someone out there can suggest how to solve this. I have searched the forum, and found a lot of abs related posts, but nothing quite like this:

I have a -94 ZJ, and recently replaced the front rotors and pads. Now, a few days later, I have a problem at the begining of every ride, and it goes like this:

-I turn engine on and start to drive. So far so good.
-While still driving at walking speed, I touch the brake pedal lightly. It immediately starts to vibrate, the pedal turns rock hard in top position, and the car pulls to the right. I hear the noise from the abs system.
-When I release the pedal, the brakes disengage, but there is still noise coming from the abs system (a humming/whining noise).
-Still at low speed, I can repeat this sequence endlessly. The problem does not disappear.
-Only when I reach higher speed, the abs system seems to "let go", meaning that the brakes behave normally, the abs noise disappears, and the abs warning light comes on. The problem does not return when I slow down again.

Any ideas on what this is, and how to fix it? Damaged/fouled speed sensor? Air in system? Would be nice to have this fixed before the Norwegian winter arrives...

Bustedback

You need to find out what the ABS code is. The diagnostic connector is below the ashtray tucked under the carpet. You need a scanner and the Chrysler number 2 connector in order to retrieve the codes. Don't just start throwing parts and sensors at it until you find the code. Did this craziness happen before you changed the rotors and pads?

dnuccio

pull the ABS relay, i did and my ZJ seems to stop better than it did before

HCH

This started after I replaced the rotors and pads. I used the car 4-5 times after the replacement before it all began. But I have had all sorts of problems with the brakes lately. The rotors were replaced because the old ones were warped and frequently overheated (can overheating damage e.g. the speed sensors?). One of the rear brake line ruptured some weeks back too, and this was fixed by a professional, including the bleeding.

Finding the error codes seems to be a bit above my skill (and tool) level. Sounds as a job for the pro again...

HCH

I can live without the abs, so pulling the relay is clearly an option. But I have read other posts where it is claimed that doing so also changes the front/rear brake power distribution.

dave1123

I think the easiest way out of this is to find out if your country's auto laws require them to work if the vehicle came equipted with ABS. Some states over here don't because ABS is not a considerable safety issue. I've heard the UK can be a real stickler on this issue. If not required, pull the relay.

You can try replacing all the wheel sensors and cleaning the tone rings, but it may not cure the problem.

Bustedback

The ABS won't apply the brakes, or keep them applied. You may have a bad hose or a sticking caliper. But find out what the ABS code is, it will give you a place to start.

HCH

Thanks to all for the response, although no one seems to have had a similar problem.
I will try to clean the tone rings and sensors first, then pull the relay as first aid if this does not do the trick. Will get the diagnostic reading next time some serious work is needed.

Any additional views on the impact on the brake force distribution fromof pulling the relay? This might be the only thing that keeps me from going permanently for this solution. Do not want to heavy rear braking on slippery roads...

HCH

The ABS does not apply the brakes (I see my original post was inacurate on this point). The ABS system engages the moment I touch the brake, but no brake force is transmitted to the wheels. Only when I hit the brakes harder does the car pull to the right, still with ABS engaged. Leads me to think that the problem is related to left front wheel sensor.

I find it strange that the ABS system seems to increase the pressure in the master cylinder when this goes on.

JJCIII

If your rotors are over heating and warping, that can cause some issues with your abs. Are the caliper pistons easily retractable?

dnuccio

hasnt changed on mine as far as i can tell. the proportioning valve (the part that distributes/varies brake pressure front and rear) isnt electronically controlled, so pulling the relay should have no effect on it

HCH

They are retractable, but I would not say easily. I can push them back using only my hands, but it requires some force.

The overheating problem was a bit strange. It was not a problem on shorter trips of say 10-20 miles, but on longer trips the brakes often started to drag and overheat (front right and rear left) to the point where continued driving was impossible. My guess was that the warped rotors caused som partial drag which gradually heated up the brakes and somehow escalated. It has not been a problem with the new rotors, but I have not really tried it out on longer drives yet.

HCH

Sounds reasonable. I will do some gravel road test drives.