Late Style Proportioning Valve

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shures
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Late Style Proportioning Valve

Post by shures » Sat Jan 30, 2010 1:18 pm

My '85 GTV6 has the late style proportioning valve. When I bleed the brakes the flow from all 4 rear bleed screws is very low. I should state that I am pressure bleeding at 5 PSI and getting maybe 1/3 the flow of the fronts.

Question: is the "Proportioning Valve" really that? I believe I read it is simply a flow reducer. In that case is there any reason I can not just disassemble and clean it? If this is truely a flow reducer then maybe it needs nothing?

Braking is fine, I am due for pads and this time rotors too. The ebrake hangs up occasionally and is a hassle to get to the "neutral" position for bleeding. I plan to replace them with calipers from Performatech when I do this but want to be sure everything is set up optimally.
Scott Shure
Ellicott City, Md
85 GTV-6
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MD
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Re: Late Style Proportioning Valve

Post by MD » Mon Feb 01, 2010 1:06 am

Shures,

There is a simple way to determine if there is any blockage to the proportioning valve. Simply by pass it with a short coupling and retest your bleeding flow. If you are doing it correctly and opening all four bleed screws at once, the combined flow should approximate that of the front.

For my road car, I have permanently by-passed the proportioning valve and find that there is a better brake balance as a result.
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AlfaTipo
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Re: Late Style Proportioning Valve

Post by AlfaTipo » Fri Sep 03, 2010 8:27 am

MD, I removed the proportioning valve while I was waiting for a new one and although the braking was OK a stop of the emergency kind left the rear end smoking and lots of noise. Very embarrassing :oops:

I would not recommend bypassing the valve.
Jef
85 GTV6 'Gina G2' Shankle cams and headers Resting Serious rebuild in the future
85 GTV6 'Gina G3' Sold but missed.
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Re: Late Style Proportioning Valve

Post by MD » Fri Sep 03, 2010 1:55 pm

Interesting how the same cars behave differently.

I have travelled thousands of kilometers with full and partial loads in the car. I also did some very high speed progressive tests after doing the conversion at speeds from 200km/h down.

I found the braking improved and was better balanced otherwise I would not have given this advice.

Whether its because I run 225 tyres on 7.5" rims at the rear providing more grip which has as a part to play I cannot say with any certainty.

On the Brick race car, it doesn't have any sort of proportioning going on either and it has superb brakes.

So I can only say what my experience tells me. Likewise you are doing the same.

Additional advice ? Try it and see on an individual basis.

Be sure to use the same pad formulation all round and be sure your front brakes are working to capacity as well otherwise you are doing the equivalent of handbrake stops
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