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post #1 of 11 Old 04-15-2009, 05:05 PM Thread Starter
Jeepguy91
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Power brake problems

Well i just swapped out my manual brakes and put in a power brake booster from a 95 yj. I went and bleed the brakes all the way around and with the motor off the pedal is hard to push. Now with the motor running it goes all the way to the floor. Does anybody know what could be causing this?

Also, where should the vacuum for the booster come from? I have it coming off the bigger end of where the line is pointing at. Should i have it somewhere else?


Need to get these working good before next weekend. Any help would be great.

Thanks,
Ben


2000 XJ limited-3" rough country, winch, winch bumper, 31" BFG at's

98 ZJ Limited 5.2- FM 40
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post #2 of 11 Old 04-15-2009, 05:10 PM
moparguyrjr
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Did you bench bleed the new mastercylinder? If you pump the brake pedal several times with the engine running do you eventually get a pedal? Just wondering if air could still be the problem.
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post #3 of 11 Old 04-15-2009, 05:25 PM
Cutlass327
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You need the engine on for the power assist to work, which is why it is hard to push when the engine is off. I use the rule of thumb that the PCV and power brake booster get the 2 largest fittings available on the engine - power brakes so it gets ample of vacuum, the PCV because smaller lines plug easier.

Keep bleeding them til there is no more spongy feel in them. If they still go to the floor make sure the rears are adjusted properly and there are no more leaks.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy

http://www.jeepforum.com/forum/f8/ri...8-cj5-1223197/
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post #4 of 11 Old 04-15-2009, 05:36 PM Thread Starter
Jeepguy91
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Well do i have the hose for the booster coming from a good spot? I have it combined right there with the pcv hose. I went around and bleed each wheel twice and still when i have it running it goes to the floor.

2000 XJ limited-3" rough country, winch, winch bumper, 31" BFG at's

98 ZJ Limited 5.2- FM 40
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post #5 of 11 Old 04-15-2009, 05:37 PM Thread Starter
Jeepguy91
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Also, how hard should it be to push the brake pedal with the engine running? It seems like there is nothing there with the engine running.

2000 XJ limited-3" rough country, winch, winch bumper, 31" BFG at's

98 ZJ Limited 5.2- FM 40
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post #6 of 11 Old 04-15-2009, 10:47 PM
Cutlass327
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Does it seem like any of the brakes work? It could be a bad master cyl. I had to replace the clutch master on my Honda once, and the new one was worse than the old one - old leaked, new bled past the seals internally...

Compare how the pedal feels to all of the other cars you've driven. Most feel about the same when working properly.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy

http://www.jeepforum.com/forum/f8/ri...8-cj5-1223197/
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post #7 of 11 Old 04-16-2009, 05:34 AM
1980tallcj7
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You're in a very common place. Many of us have done the same mod and experienced the same symptoms.
To be honest, I'm not sure how many have actually ended up with great brakes after this mod. I'm still chasing the perfect pedal.

1980 CJ7, Mule
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post #8 of 11 Old 04-16-2009, 05:46 AM
BioTex
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I didn't see where you bench bled the system. This is a must to get all the air out. IMO... The best way to bleed the brakes after this mod, is to never open the bleeder screws at the wheel cylinders to begin with. Fill the two lines up with fluid using an eye dropper or something, and if you bench bleed, you can actually bleed all the air out right there at the master cylinder.
It takes two people, just like the other way, but it is much quicker, and very effective.
You need a towel to absorb fluid that would otherwise get on your painted surfaces. But it works great.
It is too late to use this method if you already opened the bleeders at the W.C.

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post #9 of 11 Old 04-16-2009, 05:13 PM
moparguyrjr
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If it's air in the system, you should be able to pump (with engine running) the pedal several times (5 or 10) and build a firm pedal. If it won't pump up, I'd suspect a bad mastercylinder. Other possibilities; as (or after) you're pumping, if it won't make a pedal check all along the brake line system for any leaks that may be causing a problem. I've also read about the proportioning valve being an issue. Wasn't on mine but others have reported the valve being a problem.

I did the conversion on my 79, it works GREAT. I highly recommend it. You'll work this out and be glad you went to the trouble.
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post #10 of 11 Old 04-17-2009, 03:35 AM Thread Starter
Jeepguy91
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Thanks. Will give that a try. Does anybody know if the booster ever goes bad? How would i tell if it is?

2000 XJ limited-3" rough country, winch, winch bumper, 31" BFG at's

98 ZJ Limited 5.2- FM 40
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post #11 of 11 Old 04-17-2009, 03:51 AM
GPER
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Quote:
Originally Posted by 1980tallcj7 View Post
You're in a very common place. Many of us have done the same mod and experienced the same symptoms.
To be honest, I'm not sure how many have actually ended up with great brakes after this mod. I'm still chasing the perfect pedal.
Mine work great, one of the best mods I have done.
http://www.terrainstompers.com/forum...pic.php?t=2992
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