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Brake issue, mechanic stumped

Old 11-21-2015, 07:43 PM
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Default Brake issue, mechanic stumped

Hi all,

I have a brake issue and my mechanic is stumped. Hope someone here can help!! I have a 2002 Grand Cherokee 2 wheel drive with about 122k miles. Brakes were replaced about 2 months ago and everything seemed fine.

Every once in a while, while driving and coming to a stop, I get a slight shutter in the brake pedal...not rotor shake, but almost feels like it would be line related. Never have had an issue but it happens every once in a while.

The other day, I was driving and as I came to a stop, I felt a little brake shutter again...after that, the pedal went to the floor. I figured it was a master cylinder and my mechanic thought the same. He confirmed that by the fluid leak. He replaced the cylinder and test drove it. All seemed fine. I drove away and all seemed fine, but in the span of less than a mile, it felt like my brakes were slowly being applied. I turned around and headed right back to the mechanic. By the time I got back, my brakes were smoking and were pretty well seized up. Mechanic thought it might be a defective master cylinder, so he replaced it with another and bled the lines. Test driving revealed a very squishy brake pedal, almost like it was before the original replacement.

He spent today putting in a THIRD master cylinder, re-bleeding the lines and making sure everything else was correct, but this one is squishy as well. He says it goes down about halfway to the floor, maybe a little more. He said it works, but something is definitely not right.

SO, I turn to you all....any thoughts? He has said he would be willing to try another MS, either another brand or an OEM, or he would be willing to put the original one back in and refund me so I can take it somewhere else.

Any thoughts or suggestions would be greatly appreciated!!

-David
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Old 11-21-2015, 09:52 PM
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Abs system issues.
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Old 11-22-2015, 09:30 AM
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Damn! I just lost a long post! I guess I'll start again.

The brakes on my 2000 WJ have always felt squishy. Lots different than my Chevy brakes felt. I know they are working right because with the engine off and the vacuum bled down, I get a nice hard pedal and they stop the car. I've been told it has something to do with how the ABS system works, but IDK for sure. I absolutely HATE the ABS system. I can do a better job with my foot than it does! Once it engages on icy pavement, I have to shift to neutral to get it to stop.

When I first bought the jeep, the front brakes didn't seem to work at all. My mechanic tried to bleed them and we weren't getting any pressure in the fronts. He had to open all 4 bleeders to get fluid flowing to the fronts, but since then, everything seems to work fine and has for 50K miles.
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Old 11-22-2015, 03:44 PM
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could be a bad flex line swelling up. with the calipers seizing up it creates a lot of heat that transfers to the fluid and rubber flex lines.

possibility...
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Old 11-22-2015, 07:08 PM
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Okay, but that pressure is supposed to bleed off into the master cylinder. That's why it's vented.
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Old 11-23-2015, 06:19 AM
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I'm going with Caged's suspicion on this one. Replace those original flex lines.
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Old 11-23-2015, 02:21 PM
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Push Rod on the Booster not Properly Adjusted for the master cylinder
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Old 11-23-2015, 04:38 PM
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BINGO!! If the pushrod is too long, it won't more back far enough to vent the system. If it's too short, you get a low pedal.

It's a pleasure to confab with intelligent people! (DUH!! Why didn't I think of that?)

Last edited by dave1123; 11-23-2015 at 04:43 PM.
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Old 11-23-2015, 04:57 PM
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yep. i read right over that. i even went through that on the wifeys jeep a few years ago.

it may take a few tries to get it, but you will be good at it when you're done. lol
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Old 11-23-2015, 05:21 PM
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I've interchanged quite a few boosters and master cylinder combos.
I unfortunately and all too familiar with the outcomes, haha
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Old 11-23-2015, 06:01 PM
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I believe the Haynes manual has length dimensions for the rod.
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Old 11-23-2015, 07:06 PM
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Originally Posted by dave1123 View Post
I believe the Haynes manual has length dimensions for the rod.
Take a pair of calipers and measure the distance
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