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Brake proportioning valve spraying?

653 Views 10 Replies 6 Participants Last post by  93YJ4FUN
I've searched far and wide trying to find a solution to this issue, and while I found a few other people who also experienced it, I have not been able to find any solutions.

Background: 1988 YJ 4.2L. Bought a few months ago as a project - needs alot of work. When I first bought it the previous owner said that the proportioning valve was leaking, and the brakes felt like they needed to be bled. A quick test drive confirmed this.

Fast forward: I have replaced front calipers, pads, hoses, rear drums, shoes, hardware, and the hose that goes to the axle. (Not because of this issue, all of them were ready to be replaced). I topped up the master and bled the brakes. However, every time I pressed on the pedal, fluid would spray out of the front of the proportioning valve. The fluid spraying out is supposed to go to the rear I am assuming, because the fluid level in the smaller reservoir drops. I've bled many brake systems in my life and I really dont think im overlooking anything obvious. I tried gravity bleeding, the classic 2 person method, and even went out and bought an expensive vacuum bleeder. I came to the conclusion that the proportioning valve was bad. I ordered a new one, slapped it in.. same issue. Contacted seller, who said it was defective and replaced it free of charge. Got the (now third) one - put it in. same thing.. Now i'm thinking the rusty old master cylinder is bad.. (maybe putting out uneven pressure? who knows) Bought a quality replacement.. bench bled it thoroughly.. bled the system, first press of the pedal same issue. I went and bought another proportioning valve thinking maybe there was a reason the first one was only $60 instead of the usual $100+ of the others. Put it in, same issue. I took apart the old one to check for any broken o-rings or anything, everything seems fine. I adjusted the rear drums good and tight thinking maybe they were using too much fluid to fully extend, nothing. even clamped off the rear brake line at the hose and still have the same issue. I'm getting great flow to the bleeders of all 4 wheels regardless of which method of bleeding I use. The brake lines were replaced before I bought the jeep. Literally every single piece of the hydraulic brake system aside from the booster has been replaced and the issue has stayed the same. Im absolutely stumped, and would appreciate any advise that may lead me into fixing this. Im at the point of just trying to cap it off and calling it a day. I've been driving with only front brakes for weeks.
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I’m sure that rubber cover is not meant to hold pressure. It’s far too high. Take out the light switch so you can look in the hole and determine if the shuttle is centered





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Since it is new to you, and it had the problem when you first got it, have you verified the proportioning valve was plumbed correctly to begin with? If not, try this link and see if maybe the lines are incorrectly plumbed? I don't know that would cause your problem, but 4 valves latter and you're still blowing o-rings...maybe too much pressure where it doesn't want pressure.
 

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Discussion Starter · #10 ·
Hey OP- What was the solution?
I ended up getting a rebuild kit from someone who promised it would fix it. It worked great for about 5 months and then started spraying out of the shuttle valve sensor (white plastic thing in the middle)
I became totally fed up and ended up purchasing a proportioning valve for a much newer jeep and making my own brake lines to fit it in. If you're having the same issue I can get together some pictures and explain exactly how I did it. My brakes work better than they ever have.
 
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