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Old 06-30-2008, 05:35 AM   #1 (permalink)
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Jeep TJ Proportioning Valve

I just added an 8.8 with disc brakes, My rear braking is a bit weak, Found this will searching, From what I understand all you do is remove the rubber seal from the prop valve spring like in the pictures. I am running 35s can use the extra braking. Has any one done this mod? Pros and Cons? Thanks Again.
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Old 06-30-2008, 03:29 PM   #2 (permalink)
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Yes, that works well...IMO
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Old 06-30-2008, 03:38 PM   #3 (permalink)
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I have a prop valve from a rubicon that i will sell you. brand new
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Old 06-30-2008, 03:55 PM   #4 (permalink)
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The proportioning valve section of your combination valve ( valve has more than one function) is intended to bias the braking to favor the front calipers. With disc fronts and drum rears, the bias issue is further complicated by the need for higher pressure on the front calipers. The result is way too much pressure on the rear drums. The proportioning valve significantly reduces the system pressure to the rear drums. So when you install discs in the rear, you need way more pressure in the rear than the drums needed; therefore, the need to either modify your proportioning valve (remove the seal as you suggest), remove the valve completely, install a proportioning valve intended for disc/disc systems, or install an adjustable prop valve in the rear circuit.
Also, disc/drum proportioning valves generally have a residual valve to maintain a slight pressure on the rear brake cylinders. This may interfere with overall braking, when used in a disc/disc system, and probably should also be removed.
If you do remove your prop valve completely, or "gut" the prop portion, as you suggest, you may have brakes that lock up prematurely in the rear. If this happens, either install a disc/disc prop valve, or install a stand alone adjustable prop valve in the rear circuit.
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Old 06-30-2008, 04:25 PM   #5 (permalink)
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I have the 8.8 and I purchased a Rubicon Proportioning valve. The Proportioning valve is sold as a combined unit with the combination valve. I have never installed this valve as I really never felt the need. However, your mileage may vary.
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Old 07-01-2008, 04:19 PM   #6 (permalink)
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Quote:
Originally Posted by burrellsjeep View Post
I just added an 8.8 with disc brakes, My rear braking is a bit weak, Found this will searching, From what I understand all you do is remove the rubber seal from the prop valve spring like in the pictures. I am running 35s can use the extra braking. Has any one done this mod? Pros and Cons? Thanks Again.
You shouldn't have to mess with the proportioning valve. You won't notice a whole lot of difference in performance with the rear discs, but it is slightly better. I don't know anyone who's needed to mess with the proportioning valve, myself included.

I would suspect something else. Are your calipers on the correct sides?

Last edited by ChrisTX; 07-01-2008 at 04:20 PM.
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Old 07-01-2008, 04:43 PM   #7 (permalink)
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You shouldn't have to mess with the proportioning valve. You won't notice a whole lot of difference in performance with the rear discs, but it is slightly better. I don't know anyone who's needed to mess with the proportioning valve, myself included.

I would suspect something else. Are your calipers on the correct sides?
Wrong...
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Old 07-02-2008, 04:24 AM   #8 (permalink)
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Originally Posted by ChrisTX View Post
You shouldn't have to mess with the proportioning valve. You won't notice a whole lot of difference in performance with the rear discs, but it is slightly better. I don't know anyone who's needed to mess with the proportioning valve, myself included.

I would suspect something else. Are your calipers on the correct sides?
Yes the calipers are installed on right side, The brakes are working ok just a little weak, I glad yours works well for you, I was just wanting a little more brake out of the rear.
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Old 07-02-2008, 12:40 PM   #9 (permalink)
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I have never installed this valve as I really never felt the need. However, your mileage may vary.
Please enlighten me as to how installing a prop. valve will affect "mileage"...which I assume is fuel mileage.
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Old 07-02-2008, 01:04 PM   #10 (permalink)
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Originally Posted by Buccaneer View Post
Please enlighten me as to how installing a prop. valve will affect "mileage"...which I assume is fuel mileage.
That's a common interwebs phrase used as a disclaimer, inference being: Your results might be different than mine. "Mileage" is so often debated, exaggerated and disputed that it became the cornerstone of this phrase. Can also be used as YMMV (Your Mileage May Vary).


I did not mess with the prop valve for my disc'd 8.8. I have been told that the Rubi prop valve and the regular TJ pv are the same part #, but maybe somebody that knows can chime in with more info.
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Old 07-02-2008, 01:57 PM   #11 (permalink)
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Thanks For all the info, It seems to working great, I just wanted to be assured It was ok to do it. Thanks Again
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Old 07-02-2008, 02:06 PM   #12 (permalink)
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I did not mess with the prop valve for my disc'd 8.8. I have been told that the Rubi prop valve and the regular TJ pv are the same part #, but maybe somebody that knows can chime in with more info.
I put the disc brakes from a 8.8 on my 9" using the OEM proportiong valve from a 2000 TJ. The rear brakes were lacking. I removed the seal from the metering shaft in the proportioning valve, works much better...IMO
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Old 07-02-2008, 02:10 PM   #13 (permalink)
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Originally Posted by Knuckelhead View Post
I put the disc brakes from a 8.8 on my 9" using the OEM proportiong valve from a 2000 TJ. The rear brakes were lacking. I removed the seal from the metering shaft in the proportioning valve, works much better...IMO
Thanks For the help
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Old 07-02-2008, 03:01 PM   #14 (permalink)
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Originally Posted by GSW View Post
That's a common interwebs phrase used as a disclaimer, inference being: Your results might be different than mine. "Mileage" is so often debated, exaggerated and disputed that it became the cornerstone of this phrase. Can also be used as YMMV (Your Mileage May Vary).


I did not mess with the prop valve for my disc'd 8.8. I have been told that the Rubi prop valve and the regular TJ pv are the same part #, but maybe somebody that knows can chime in with more info.

HAHA, Never heard that before... but makes sense now! Carry on.
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Old 07-02-2008, 05:26 PM   #15 (permalink)
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I went and bought a 97 xj proportioning valve tweaked the mounting bracket,and the thing works great
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