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Discussion Starter #1
Initially I had a problem with the power assist on my 2000 Range Rover. I replaced my accumulator, changed the brake fluid and blead the brakes. The brakes are working now but the brake, ABS and TC lights come on. Sometimes right away after starting the engine and sometimes after I start to dirve. I've dirven the truck for about a week now and have noticed brake fluid leaking from one of the brake components mounted just below the master cylinder/modulator mounted on the rear of the left inner fender (see photo). Today I noticed quite a bit of fluid on the floor just behind the front wheel. Can anyone tell me what this component is and why it would be leaking?
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

That looks like a load proportioning valve. It definitely shouldn't be leaking any fluid, so if you're certain that it's leaking from there, you probably have something loose, perhaps like a nut or something.

Having said that, since the brake unit is under quite a bit of pressure, if you have a leak, you should be able to pinpoint where the leak is coming from. Perhaps your next best course of action would be to have somebody press on the brake while you're looking around the brake system. I would highly encourage you to wear protective glasses as you don't want pressurized brake fluid in your eyes!

Good luck
 

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Discussion Starter #3
Re: ABS - Warning Lights On & Fluid leak in the brake system

Thanks TheoR. I thought it might be a proportioning valve. Besides the mountng bolts it looks like there are only two brake lines that are connected to it. Both of the fittings are dry as well as all the other brake components around it. Seems to be leaking from the bottom when the truck is just sitting. I placed a piece of paper towel under the proportioning valve and within an hour or so it was saturated. I'll have someone press on the brakes like you suggested and look for a leak under pressure.
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

Theor isn't joking. You are dealing with a very high pressure system. I've worked on systems on aircraft that run on a similar pressure to that of the RR braking system. I have seen some very nasty things happen to people with leaking pressurized hydraulic fluid. You won't take what I say lightly if you've seen someones arm swell up with fluid because the pressure is so high and the fluid is moving so fast that it pierces the skin and then fills up the limb. So, BE CAREFUL!!!! If you depressurize the braking system by pushing the brake pedal at least 30 times, you will be fine.
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

Hi

You have to change the o-ring and hope it closes off.

If you are handy you could repair it as in the following thread.

viewtopic.php?f=3&t=33277

Regards

Jos
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

Thanks for the input, just what I needed before I tear into anything. The site Jos pointed me to explains a lot.

Allen
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

I removed the PCRV Valve and found the leak as expected. I'm not sure how this component gets by quality control because there is obviously a deficiency in the design. The mounting bracket that screws to the casting also clamps down on the o-ring creating a seal. Looking at the first photo you can see the rusty area at the bottom that cuts right across the o-ring grove. In the second photo you can see most of the o-ring outside the bracket. The third photo you can see the seating area on the bracket is probably less than .030", which compounds the problem. I cleaned up all of the parts and re-surfaced the faces of both the casting and the bracket to be sure they are perfectly flat. I also elongated both mounting holes in the bracket to make sure the bracket would cover the entire o-ring. The o-ring looked good so I turned it over and re-used it. When I assembled everything I made sure the small area on the bracket was in proper contact with the o-ring and torqued the two bolts. The fourth picture shows the internal components. So far I don't know if this will resolve the warning light issue. I'll see what happens after I bleed the brakes.

Allen
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

Thank-you for the information provided to contributors of this post. I am interested to know if elongating the holes allowed for more of the o-ring to be clamped and that this did not impact the innards as to how they move under brake pressure. I certainly agree with your assessments of this parts design.
 

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Discussion Starter #9
Re: ABS - Warning Lights On & Fluid leak in the brake system

Yes, elongating the holes by .025" or so provided enough movement to clamp more of the o-ring. Sorry, I didn't get a picture of this. I used a small grinder and elongated the holes a little at a time to making sure the small flat area on the bracket sat right on top of o-ring. As for the innards, my assessment is that there is a little clearance where the spring fits over the plunger and button, plus there will be some deflection in the spring. After I bleed the brakes I'll know more but I can say that it went together without any binding or interference.

Allen
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

After I repaired and installed the PCRV valve I bled the brakes. Everything was fine until I got to the final bleed of the front left. Once again, I had brake fluid leaking from the PCRV valve. I really should have known better than to trust the old o-ring but because a new EPDM o-ring was not readily available and the old one appeared to be fine, I just reused it. After taking the PCRV valve apart again and carefully measuring the o-ring cross section I could see that it was permanently deformed, flattened to .050". This is the same dimension as the o-ring groove in the casting that also measures .050". It allowed nothing for no compression. This issue is further complicated by the groove width in the casting which measures .092" wide (1.065 OD / .880" ID). From my experience, this is way out of line for sizing an o-ring in a high-pressure system like this. Anyway, you can do the math. I've now ordered a new EPDM o-ring with a .070" cross-section and an inside diameter of .875" in a medium hard durometer. I'm still not comfortable with the grove being so much wider than the o-ring but I expect it should be OK with the new o-ring and the changes I made in the bracket. So I’m out of commission for another five days or so until I get the o-ring and some garage time.
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

Thanks for the update. A classic case of something only working if everything is perfect. O-rings are called upon to do more than they should. I hope the car mfg'sauto engineers have reviewed this posting.
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

I installed the new o-ring yesterday. The first picture below shows the casting and the mounting bracket with the old o-ring installed. The second picture shows the new o-ring and a .014” space between the casting and mounting bracket that will allow for good compression of the o-ring. Before I reassembled the unit I checked to see how flat the surface of the mounting bracket was by applying layout dye to the bracket and using 1000 grit sandpaper with a surface plate. You can see from the third picture that it wasn’t perfectly flat so I resurfaced it as seen in the fourth picture. Everything looked good so I reassembled and reinstalled it.

With everything back together, I started to bleed the brakes but once again when I got to step 20 in the procedure (the left front caliper) I had brake fluid starting to appear on the floor. In a mater of a minute or so the puddle was 12” in diameter.

This PCRV Valve is not all that complicated so I stopped to think about how it’s suppose to work. The piston has an o-ring and a seal (like the one you’d see inside a typical master cylinder). I came to the conclusion that brake fluid should not leak past the o-ring or the seal because it will eventually fill the backside of the piston where the spring is located. If this area fills with brake fluid it will not allow the piston to move and the PCRV Valve will not function. In my case, it takes about 30 to 40 minutes to fill this chamber and that’s about the time it takes to get to step 20 in the bleed procedure. The seal I’ve been working on is probably nothing more than a dust seal. I said in an earlier post that I thought it was a deficiency in the design but now I’m thinking it was designed this way on purpose so it would leak if the o-ring and seal on the piston ever failed.

Today I removed the PCRV Valve and the first thing I noticed is that the new o-ring was pushed out of the groove and it was leaking there. I took the valve apart and found fluid on the back side of the piston and there wasn’t much resistance when I pulled the piston from the bore. A close look at the piston seal I could see it was worn where it makes contact with the bore and the o-ring was also flat and worn. There is also a small plunger running down the center of the piston that operates some internal ports and this also has a small seal to prevent leaking to the back side of the piston. If I blow on mine I can hear the leak.

At this point I believe I’ll just have to buy a new PCRV Valve because I can’t source out the special piston seals. Possibly these could be replaced with o-rings but I wont take any chances when it comes to the brakes.[attachment=4:14z8h69j]W old oring.JPG[/attachment:14z8h69j]
 

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Re: ABS - Warning Lights On & Fluid leak in the brake system

Best to hunt down a good 2nd hand unit, I nitice that there's not enough material to completly cover the o ring so in effect its a defective part that shouldnt have made it past QC
 
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