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Unread 06-22-2013, 08:15 PM   #1
killakeane
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Spongy brakes/no brakes

Hey, i replaced my brake hose today, and bled the brakes numerous times on each side as well as gravity bled them. The brakes feel really strong when the jeep is turned off but as soon as it starts running the brakes go basically dead and too the floor. i can't figure out what's doing it considering the amount of times i bled them. any input?

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Unread 06-22-2013, 08:29 PM   #2
TSEJEEPERS
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Any leaks when you pump the brakes?
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Unread 06-22-2013, 08:33 PM   #3
killakeane
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None, at least none visible. I had a leaky hose that's why I replaced that. The master was fine prior to my hose leak so I don't believe it's the master either.
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Unread 06-23-2013, 01:19 PM   #4
killakeane
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Anyone know what's wrong with it?
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Unread 06-23-2013, 01:24 PM   #5
PA_YJ19
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Sounds like a bad booster if ur pedal is dropping to the floor. There's probably a leak in it sumwhere... It holds air so u won't physically see it, have sumone push the pedal down and put ur head by the booster. If u hear ne whistle type noise or air escaping newhere then it's not doing its job. When u press the pedal down u should feel the pressure build up not release, as it sounds like its doing in ur case.
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Unread 06-23-2013, 01:42 PM   #6
killakeane
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i don't think its a leak, wouldn't i be loosing fluid from the mc?
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Unread 06-23-2013, 01:51 PM   #7
pasinbuy
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What all did you do to your brakes other than the hose?:
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Unread 06-23-2013, 02:10 PM   #8
jhrebs
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There is a rare chance that the MC could have gone. Yes it did work before you did your line, but maybe a new line, bleeding alot......YJ's are old and temperamental. I would guess booster or MC, only by process of elimination
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Unread 06-23-2013, 02:10 PM   #9
PA_YJ19
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Quote:
Originally Posted by killakeane
i don't think its a leak, wouldn't i be loosing fluid from the mc?
Not if it's the booster, the booster just holds air. Ur master holds the fluid.
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Unread 06-23-2013, 06:28 PM   #10
killakeane
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was talking to my uncle who used to work on cars a lot, he said it's not the booster if it were the booster it would be hard at all times both running and while off, i also talked to my fiances father, who has ground up a few jeeps hot rods etc and he thinks it might be the shoes in the back, ill try rebleeding as well as adjusting the rear shoes with the spoon? i believe thats what it's called - not sure - this will be my first time doing it. i'll let ya'll know what the outcome is when i figure it out, and if i don't well i'll be referring to the forum for more details. thanks for the input so far gents.
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Unread 06-23-2013, 06:37 PM   #11
laybackman
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If the master cylinder 'sucked air' it now has to be bench bled or you will never get brakes to bleed.
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Unread 06-23-2013, 06:40 PM   #12
TSEJEEPERS
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Not harping on the leak thing but, clean off the area where you put the new hoses on. Where the hose connects to the hard line and the caliper.
Have someone pump the brakes up. Pump it 3 times then hold. If there is any evidence of brake fluid there is a leak.
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Unread 06-25-2013, 05:13 AM   #13
Dewster196
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Which way did you bleed the brakes, you are supposed to start at the bleeder furthest from the master and work to the closest. Just a thought.
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Unread 06-25-2013, 08:59 AM   #14
jay-h
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It's normal, if you have bled off the vacuum of the booster, for the pedal to lower when the engine starts. This is the result of the booster becoming active. Obviously shouldn't go all the way to the floor however, but the usual failure mode of boosters is vacuum leak which would manifest itself in a higher (unboosted) pedal position.

Edited to add: What you are feeling when the vacuum is bled off is the ACTUAL pedal and free play. If that is solid, you do not have a bleeding issue. Once vacuum is applied the servo mechanism allows some degree of travel and converts that travel to valve boost against the master cylinder. The normal mode of failure for boosters is vacuum leak, but if you can shut off your engine and go back 20 minutes later and still have vacuum boost, you don't have much leak.

Mine has a significantly different position from vacuum to no vacuum, actually more that I'd like, but it has always been that way. I don't know if wear on the servo can cause excessively low travel, or that's just the way it is designed... I've never heard a discussion of servo wear other than vacuum leaks.
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