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Mystery brake issue

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Old Oct 29, 2017 | 05:09 PM
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Default Mystery brake issue

98 XJ. I had a sticky caliper. Started by replacing both front calipers and rotors and bled them. Then, I had almost no braking power at all. Replaced master cylinder, rear wheel cylinders and shoes, as well as rear brake lines, bled all 4 brakes, adjusted rears. Still nothing. Replaced power booster, bled all 4 brakes, still soft. Adjusted rod in power booster. Still soft. No leaking fluid anywhere. WTF?

Last edited by paulutions; Oct 29, 2017 at 05:30 PM. Reason: Forgot a part
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Old Oct 29, 2017 | 05:19 PM
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vacuum hose to the booster leaking ?

marc

edit: does your idle change when pressing the brake pedal ?, did you bench bleed the master cylinder ?

Last edited by LadyKenai; Oct 29, 2017 at 05:26 PM.
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Old Oct 29, 2017 | 05:30 PM
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Old Oct 29, 2017 | 05:32 PM
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Originally Posted by LadyKenai
vacuum hose to the booster leaking ?

marc

edit: does your idle change when pressing the brake pedal ?, did you bench bleed the master cylinder ?
I replaced the vaccum line. But, yes, the idle does change when I apply the brakes and the break light goes on and off intermittently
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Old Oct 29, 2017 | 05:34 PM
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Originally Posted by LadyKenai
vacuum hose to the booster leaking ?

marc

edit: does your idle change when pressing the brake pedal ?, did you bench bleed the master cylinder ?
Originally Posted by paulutions
I replaced the vaccum line. But, yes, the idle does change when I apply the brakes and the break light goes on and off intermittently
Also, I did bench bleed the master cylinder.
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Old Oct 29, 2017 | 05:37 PM
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if your idle changes while pressing the brake you have a vacuum leak somewhere

marc

let me rewrite this..

edit: if there is a 'noticable' idle change when pressing the brake and its outside 'specification limits' you are probably looking at a vacuum leak

Last edited by LadyKenai; Oct 31, 2017 at 08:12 PM.
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Old Oct 29, 2017 | 05:59 PM
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^^ that. And are the bleeders on your calipers on the top or bottom?
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Old Oct 29, 2017 | 11:14 PM
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An idle change when pumping the brakes is normal so ignore that. Do make sure that you put the front calipers on the correct sides, bleeders above the hose.
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Old Oct 29, 2017 | 11:31 PM
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In my past 3 Jeep's I have never had an idle change when pumping the brakes. That's my solo input. Maybe someone can explain this better to me?
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Old Oct 30, 2017 | 08:10 AM
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Um. I feel stupid. Yes, I did put the calipers on the wrong side. I just went by the L & the R that the nice guy at Oreilly's wrote on the boxes & forgot all about it. Thanks for reminding me, y'all. I'll let you know if that's the problem.
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Old Oct 30, 2017 | 10:02 AM
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The upside down calipers is your issue. Since the bleeder isn't at the top there's a lot of air in there.

A tip to not loose fluid while swapping calipers: Using a bar or something, there's actually a tool for this too, hold the brake pedal down a bit while doing the work. With the master cylinder pistons pressed away from their normal resting point they block fluid flow. You may have a small amount of pressure so when you open the first bleeder expect a small squirt of fluid, after that you'll have almost no leakage while things are apart. I've had systems open for days and didn't loose any fluid. Be aware that the brake lights will probably be on so if you're gonna have it apart for many hours you might drain your battery.

In the video posted he says the front reservoir for the front brakes, that's backwards. The front reservoir is the rear brakes.
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Old Oct 30, 2017 | 12:23 PM
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Originally Posted by paulutions
Um. I feel stupid. Yes, I did put the calipers on the wrong side. I just went by the L & the R that the nice guy at Oreilly's wrote on the boxes & forgot all about it. Thanks for reminding me, y'all. I'll let you know if that's the problem.
Mixing the left and right caliper happens more often than you might think. The bleeder always faces UP.
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Old Oct 30, 2017 | 03:11 PM
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Yup. That was it. Switched calipers, bled the brakes, and she's good as new. Thanks, y'all.
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Old Oct 30, 2017 | 03:32 PM
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if you had a sticking caliper you should probably change the front hoses too since you will be pulling the calipers again.
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Old Oct 30, 2017 | 05:02 PM
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on 2 of our jeeps the idle doesnt change when i press the brake the other jeep does and i know for fact its the booster is leaking. if you should ignore that? thats up to you

marc
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