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Unread 06-16-2013, 03:22 PM   #1
JasonStebbins
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1997 ZJ 
 
Join Date: Jan 2009
Posts: 3,138
No Pressure To Rear Brakes

I posted a thread awhile back about this problem, but it went away on it's own for about a month. Now it's back. With a vengeance.

While driving Friday the pedal went to the floor and the BRAKE light came on. I checked the fluid and it hasn't moved at all in the last 5 weeks. There are NO leaks anywhere in the lines, I've checked more times then I probably needed to.

After researching a little bit I replaced the proportioning valve thinking maybe it locked up, disabling flow to the rear. This morning after I re-bled all 4 lines from rear to front, the rear bleeders don't squirt any fluid. It just seeps a tiny bit when I loosen them which I figure is just fluid sitting in the caliper.

I don't seem to have any symptoms of a bad master cylinder because it goes to the floor every single time and there's no fluid loss anywhere.

I really don't want to take it to a garage and get charged for something that is probably really simple. Is there a giant air pocket somewhere? I tried line bleeding the ABS pump with no success. The booster is putting out tons of vacuum suction when I unplug the hose.

Am I overlooking something or is there a bigger problem that the dealership needs to deal with? The rear rotors are ice cold after driving around town, and the front are working overtime and the wheels start getting warm.

Help my poor ZJ.

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Unread 06-16-2013, 03:32 PM   #2
Maine1994ZJ
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1993 ZJ 
 
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Location: Phippsburg, Maine
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Sounds like you have the brake lines reversed at the proportioning valve. Front line on the rear port and rear line on the front port.

Been there, done that....
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Unread 06-16-2013, 08:37 PM   #3
JasonStebbins
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Quote:
Originally Posted by Maine1994ZJ View Post
Sounds like you have the brake lines reversed at the proportioning valve. Front line on the rear port and rear line on the front port.

Been there, done that....
It started doing it again last week. Been fine for about a month. Haven't moved the lines until today and I marked them all so I wouldn't do that. I've never messed with the valve since I bought it.

I don't understand why the brake pedal goes to the floor now though. The front brakes stop me but there should still be pressure in the system even with just the front brakes working.

I read something about the ABS pump having to be bled? But I disconnected every fuse and relay the day I bought it and it's never been a problem. Something is wrong somewhere.
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Unread 06-16-2013, 09:55 PM   #4
jabba974
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1996 ZJ 
 
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Location: Ionia, MI
Posts: 246
Sounds like a bad master cylinder to me...I doubt its a bad booster, when those go bad ussaully the brake pedal is hard..
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Unread 06-16-2013, 10:45 PM   #5
JasonStebbins
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1997 ZJ 
 
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Quote:
Originally Posted by jabba974 View Post
Sounds like a bad master cylinder to me...I doubt its a bad booster, when those go bad ussaully the brake pedal is hard..
I grabbed the MC along with the valve at the junkyard just in case. I'll throw that on tomorrow and see if anything changes.
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Unread 06-16-2013, 10:53 PM   #6
eagsc7
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Location: Sweetwater Cyt, WY
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Are you sure that the one from the JY was a good one? Was it tested?
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Unread 06-16-2013, 11:06 PM   #7
JasonStebbins
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Quote:
Originally Posted by eagsc7 View Post
Are you sure that the one from the JY was a good one? Was it tested?
Nope. But it changed absolutely nothing when I swapped the JY one in. I suppose they could both have the same problem, but doesn't seem very likely. I'll update tomorrow after I swap the master cylinder.

Pedal goes to the floor, BRAKE light is permanently on now. Zero pressure.
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Unread 06-17-2013, 01:31 AM   #8
JasonStebbins
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1997 ZJ 
 
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Update :

I couldn't fall asleep so I decided to go out and swap the JY master cylinder. I got my pressure back.

I'll have to bleed all four lines because it's still a little spongy obviously from disconnecting everything but it definitely fixed the problem. It stops normal again and it starts braking as soon as depress the pedal, and it didn't go to the floor once on my test drive.

So if you have the symptoms I did, take a trip to the junkyard and find a donor ZJ and swap it out!

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Unread 06-17-2013, 06:16 AM   #9
96zedjay
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1996 ZJ 
 
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Junkyard master cyl? Ya scare me man.
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Unread 06-17-2013, 04:00 PM   #10
JasonStebbins
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Well I was just throwing a couple parts at it to see if I got any change in symptoms.

The ZJ I've been picking through has 121,000 and is so clean it's a shame to be there. The windshield says bad front differential.

It's a black limited edition with all the bells and whistles. The entire engine compartment looks like it's been scrubbed with simple green it's so shiny. All the fluids look to be brand new. We pulled the radiator for my friend's ZJ and it looks like it came out of the box. Lime green coolant, crystal clear brake fluid, gold oil. Must have stopped driving it abruptly.

But anyway, I have never had brakes like I do now since I bought it 3 years ago. There has always been a little pedal travel before they engaged, now I can honestly compare it to my girls Alero brakes. It's amazing. Must have had a small internal leak for some time.
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Unread 06-17-2013, 04:43 PM   #11
96zedjay
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1996 ZJ 
 
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Location: Cincinnati, Ohio
Posts: 293
Thats cool... Anytime you lose you Pedal and there is no fluid leak/loss its the Master... And it's not uncommon to come and go.
My J-10 has been doing it for the last 6 months on and off..... Too lazy to change it. He He Don't drive it much. Gas mileage sucks.
10 to 14mpg compared to my 5.2 ZJ 15 to 20mpg :-)
Wish NY was closer, sounds like that Limited has some parts I need.
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Unread 07-09-2013, 07:57 PM   #12
eagsc7
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Location: Sweetwater Cyt, WY
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Just thought of this JY Master Cyl is ALWAYS A BAD IDEA!!! You don't know How it has been used, AND how Soon it will FAIL! Also, a NEW Master Cyl from Oreileys ran me 45$ Without ABS, and $70 With ABS this last week. Course, After changing the cyl, I need to bleed the lines now...
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