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  #1  
Old February 9th, 2019, 14:42
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jeeping4fun jeeping4fun is offline
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Brake booster and MC swap issue

Hey guys

I have a 87 MJ that I swapped a 96 booster and MC into. I just took it for a drive and when pushing the brake I get nothing until the last inch or so then it goes full brake. Like lock the tires up lol.

The booster and MC were new. I left the original praportioning valve. Bench bled the mc and bleed almost 64 oz of fluid through.

I also put new calipers and brakes pads/rotors on.

Any suggestions?

Also when I hit the brakes with it off I can hear a suction sound coming from booster/mc area.

Thanks
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  #2  
Old February 9th, 2019, 16:03
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paulhead paulhead is offline
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Re: Brake booster and MC swap issue

That suction sound may be a bad booster, I went thru 2 before finding a good one. Also thoroughly bleeding the brakes is essential. I had a to more than once.
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  #3  
Old February 9th, 2019, 18:09
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Re: Brake booster and MC swap issue

Damn ok. Its brand new but who knows. I'll take it back and get another new one.

I just bled them again and still the same. I'll try it again in a couple days and see if it just has that much air. Crazy I've put like 80oz through it now.

Thanks
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  #4  
Old February 10th, 2019, 06:58
Jim Malcolm Jim Malcolm is offline
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Re: Brake booster and MC swap issue

You may have an air bubble trapped in the proportioning valve. Just loosen the end, fluid will come out. Be careful, there's a spring behind it, so it can be a bear sometimes when your hand is covered in fluid. At this point you're half way to putting the proper proportioning valve in their. You don't need to replace the body, just the screw in piece and the spring out of a ZJ. I prefer not to wear out my brakes prematurely when the fix is so easy and inexpensive.
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  #5  
Old February 10th, 2019, 07:23
RCP Phx RCP Phx is offline
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Re: Brake booster and MC swap issue

Did you get the pushrods(there are 2) adjusted properly?
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  #6  
Old February 10th, 2019, 09:48
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Re: Brake booster and MC swap issue

I'll try to crack the valve. I did the rear disc brakes on my xj and upgraded the spring. Does the ZJ spring fit in the old style propotioning valve?

I did not adjust any pushrod. Where are these located?
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  #7  
Old February 10th, 2019, 09:53
RCP Phx RCP Phx is offline
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Re: Brake booster and MC swap issue

Quote:
Originally Posted by jeeping4fun View Post
I did not adjust any pushrod. Where are these located?
You've got one between the pedal and the booster, and one between the booster and the master cylinder.
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  #8  
Old February 10th, 2019, 09:58
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jeeping4fun jeeping4fun is offline
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Re: Brake booster and MC swap issue

I didnt adjust either. I did add a 1/4" spacer between the booster and fire wall so I didnt need to trim the fire wall. Also by doing that the length of the rod inside the cab would be the same. If I didnt the pedal all the way up would have a 1/4" of pressure into the booster.

I also didnt mess with the one from the booster to mc.

I am looking at it again now and the MC is the one making a noise when I let off the pedal. Sounds like its ducking air. I cant find a leak anywhere. Damn thing.
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  #9  
Old February 10th, 2019, 10:24
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Re: Brake booster and MC swap issue

Well I think the sound is inside the MC. Waiting on my wife because I can push the pedal and run to the front in time.

Also I got those quick bleeders so i could bleed them myself. Tried to save myself from the peanut gallery. "How long will this take" "my leg is tired". Anyways gonna replace those and bleed it with two people. If I cant get the air out then I'll assume the MC is bad and replace it...again. it will be a couple weeks before I have time but I'll update once I find the problem.
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  #10  
Old February 10th, 2019, 11:36
RCP Phx RCP Phx is offline
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Re: Brake booster and MC swap issue

Quote:
Originally Posted by jeeping4fun View Post
I am looking at it again now and the MC is the one making a noise when I let off the pedal. Sounds like its sucking air. I cant find a leak anywhere. Damn thing.
Quote:
Originally Posted by jeeping4fun View Post
Well I think the sound is inside the MC.
It's not to likely on the sound being the MC would/could be air. There is a gasket that can leak air between the MC and the booster.
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  #11  
Old February 10th, 2019, 11:55
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Re: Brake booster and MC swap issue

Ok I got an extra gasket. The MC came with one and the booster came with one. I'll swap it out and see before completely changing out the MC.
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  #12  
Old February 12th, 2019, 07:30
RCP Phx RCP Phx is offline
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Re: Brake booster and MC swap issue

So these are ZJ rear disc's installed on a D35?
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  #13  
Old February 12th, 2019, 10:00
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jeeping4fun jeeping4fun is offline
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Re: Brake booster and MC swap issue

No I have a dana 44 with drums. I just upgraded the MC and booster to a 96 XJ.

My other jeep XJ I did a rear disc conversion and upgraded the spring.

Since my MJ is drum in the rear that's why I was asking if I should do the spring? I never heard of doing it in any of the mc booster upgrade threads.
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  #14  
Old February 12th, 2019, 10:15
Borgli Borgli is offline
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Re: Brake booster and MC swap issue

For me the pushrod was a bit short so(if I recall right) I unscrewed the one in there and replaced it with a longer bolt that I cut the head of. I went from braking 300ft early to almost slamming my face into the steering wheel. Can't believe I waited 2 years to check something so simple. Anyways, check your pushrod.
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  #15  
Old February 12th, 2019, 10:18
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Re: Brake booster and MC swap issue

Ok got it. I'll check when I take it apart again... thanks for the input
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