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Old 08-31-2007, 01:58 PM   #1
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Brake issue

I am stumped.

'91 YJ Sahara with 4.0L

The Jeep sat while I did some engine work. (engine runs great now). Then I took it out for a test run only to find out that a caliper had seized up. Came home and had lots of smoke pouring out of the caliper area.

No problem, replaced the rotors, pads and front calipers. Jeep parts are cheap.

Add a rusted brake line rupturing during the bleeding process just to add to the frustration. Replaced brake line.

Unfortunately, I can't get the brakes to work right. I can pump the pedal up and it will hold pressure. I can back the brake pedal off halfway and then push it down and it works great. When the pedal is allowed to come all the way back up and then I press it down the pedal immediately goes straight to the floor. I can then pump the pedal up to pressure in a stroke or two.

I thought I might have cooked a seal in the brake master cylinder. I figured old brake fluid with some moisture might have boiled up the lines into the master cylinder. So I replaced the master cylinder and bled per the instructions. Jeep parts are cheap.

The pedal still goes straight to the floor for the first stroke and then comes up hard and holds after subsequent strokes.

Is there a peculiar bleeding technique with these jeeps that I am missing?

There is some sort of distribution assembly downstream of the master cylinder. Could that be at fault?

Thanks for any info.

-Britton

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Old 08-31-2007, 02:34 PM   #2
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Did you ever bleed the break lines at the calipers? YOu didn't touch the rear lines right?

Bleed the passenger caliper first and then the driver one to make sure no air is in the lines. Then check the master cylinder to make sure its not sucking any air or has any bubbles in it.

If everything was done right, it sounds like a break power booster problem, not a master cylinder problem.

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Old 08-31-2007, 02:43 PM   #3
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did you bleed the MC first before you bled all the wheels?
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Old 09-01-2007, 07:03 PM   #4
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Thanks for the responses.

Originally, I bled the front two calipers, passenger side first.

Then I pumped fluid from the caliper back up to the master cylinder thinking I had an air bubble trapped somewhere.

Then I replaced the master cylinder, bled the master cylinder and then bled all calipers starting from the rear passenger, then rear driver, then front passenger, then driver side.

Then just for the fun of it I pumped fluid up all the lines in the same order.

Brake power booster problem?... That sounds depressing but thanks for the suggestion.

-Britton
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Old 09-01-2007, 08:02 PM   #5
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About a month ago, we had one towed into the shop with the same symptoms. Turns out that if the calipers are installed on the wrong side, then the bleeders are on bottom. Bleeders have got to be on top for the air to come out. Jeep calipers will install on the wrong side pretty easy, if you don't look for the bleeder screw.
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Old 09-01-2007, 08:11 PM   #6
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Also, understanding the internal workings of a Vacuum Brake Booster, I would probably rule that out. If you had a pedal till you changed the front brakes, go back and recheck your work.
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Old 09-05-2007, 12:07 PM   #7
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Boy do I feel stupid.

You hit the nail exactly. The calipers were on the wrong sides.

Did a test run and the brakes are great. While on the test run I developed a fuel leak though... <sigh>

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