vibration in the brake pedal -
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post #1 of 7 Old 01-08-2003, 01:48 PM Thread Starter
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vibration in the brake pedal

When I go past 15 mph, and then hit the brakes to stop the car does some sort of halfway ABS function. The brake pedal vibrates, the vehicle doesn't stop near as fast, and keeps going on, until it slows to 2 mph then all the vibration stops. This happens on dry pavement, literally every stop. When I hit ice and the wheels lock up, true ABS kicks in and the pedal really shakes, not the same feeling. If I drive at about 10 mph for 15 - 20 seconds the ABS light comes on, and the problem stops, but unfortunately so does my ABS protection. Any ideas?

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post #2 of 7 Old 01-08-2003, 06:10 PM
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i think you might have warped brake rotors, it's a really common problem in ZJ's (93-98). in my experience the whole car shudders when braking but it might trasfer just to the pedal if it's not too severe. just go to a mechanic to get it checked out. they'll know what you're talking about.


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post #3 of 7 Old 01-09-2003, 05:45 AM Thread Starter
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Thanks for the idea, but I know that it's something to do with the ABS system. For one thing if it were rotors, hitting the brakes at highway speeds would give a shutter. But another thing is that if I drive the car at 10mph, while it's in the midst of the annoying vibratation with my foot off the pedal it's still doing it. If continued at the same speed for 20 sec it will stop and the ABS light comes on and the problem is fixed. It doesn't vibrate the pedal any more.

I appreciate your ideas though.
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post #4 of 7 Old 01-09-2003, 04:16 PM
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You did not mention what year your jeep is, but since this could be a saftey issue I would take it into a dealer and see if this is covered under warranty. Often saftey and emissions components are covered for a longer period of time than the normal 7/70 or 3/36 warranties. You can pull the fuse on the ABS system to see if this clears up the problem. That may help isolate the problem.

I would not completly rule out the warped rotor theory. Mine vibrated at slow speeds before they stared vibrating at high speeds. My ABS light never came on though.

Good Luck

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post #5 of 7 Old 01-10-2003, 08:03 AM Thread Starter
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All good thoughts. My Jeep is a 98. Problem is that it has 150k miles. So I'm sure the fix is on me. That stinks too because it breaks left and right. Anywho, your right brakes are an important item to have on a car. So I have an appt scheduled for next week. The fuse on the system good idea, I tried that once before. I saw 2 fuses, one for the pump and one for (???). Neither looked like a master system fuse. I disconnected the battery negative cable and left it off for an hour, but it has an alt power source because not even my radio settings were off by the slightest (but yet it can't remember my seat position from one time to the next). I know it is the ABS system because once I get the ABS light to come on it stops fine, no problems. I plan to see what the mechanic says and then go buy the part at a junk yard. I'm sure it will be something in the ECU and cost a couple thousand, whereas I can get a used part for a couple hundred, and have about the same warranty.
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post #6 of 7 Old 01-13-2003, 07:51 PM
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Z - I had a similar problem with my '96 GCL. Turned out to be the rear parking brake liner separated from the metal shoe and broke the driver side rear wheel speed sensor (there is one on each wheel that the ABS uses to detect lockup). The computer could not sense the rear wheel spinning so it was trying to engage the ABS each time I was on the brakes below 20 mph. Good luck!

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post #7 of 7 Old 01-14-2003, 06:28 AM Thread Starter
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Yeah, I took it to the dealer yesterday and they said it was the sensor on the back too. But the crazy thing is that I just replaced that sensor a couple weeks ago and this problem continued like before. They are replacing the new sensor, so if it was the sensor then I guess the other one was bad out of the box.

Good thoughts though!
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