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Old 01-23-2014, 09:58 AM
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Adjustable Proportioning Valve

I'm building an Austin A40 Street Rod w 350 SBC, 5 speed manual overdrive trans, Helix MII front w 11" disc brakes and 10 bolt posi rear w drum brakes from a Chevy S-10 Blazer set up w a triangulated 4 link and coil overs. The brake master cyl is from the S-10. I plan to drive it quite a bit. I bought a Wilwood adjustable Proportioning Valve. Should I mount the PV in a place so I can adjust it while driving or is it one of those things where, once it is dialed in you never touch it? What do you guys think? I suppose once in a while you could dial out the rear brakes so you could do a heck of a burn out.

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Old 01-23-2014, 11:09 AM
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Usually once you have it set, you dont touch it. If you want to lock the front brakes for a burnout, then use a lineloc.
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Old 01-23-2014, 11:16 AM
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Just put one in my Bronco. I've not driven on it yet. One thing I wish I'd done differently is to mount it below the master cylinder to help in gravity bleeding at the calipers. Mine is slightly above, still bleed out fine.
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Old 01-24-2014, 06:38 AM
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As I understand it, the sole purpose of the PV is to keep the rear tires from locking up before the fronts. In a panic stop, The tires that slide first steer the car. You do not want the rear end to beat you to the scene of the accident.

For cool burn-outs, how about adding an electronic e-brake solenoid to the front line?
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Old 01-24-2014, 10:36 AM
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All depends on the car use. If not racing (or setup suspension-wise for) then there's no reason to put in a proportioning valve that I can think of.

In drag racing (RWD cars) with very large rear tires and very small front tires the majority of braking force shifts to the larger rear tires. So you want a lot more braking force going to the rear tires but not to the front. You don't want to lock up the small front tires (which would happen at much lower braking than the rears). Therefore you pull force away from the front.

The valve is usually in a place that is easy to get to so it can be dialed in where you want it. Also, track conditions change so that would also mean a possible tweak at the valve too.

Just about all PV limit the amount that can be pulled out. Usually IIRC it is about 57% max.

For burn outs in a RWD car you just use a line-lock solenoid on the front brakes.
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Old 01-24-2014, 07:17 PM
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Set it and forget it so you can learn the car and so it will respond to you consistently. The only time you would need to adjust it on the fly is if you wanted more or less brakes power in the rear. One example of when this would occur is if you increased the rear weight significantly then you could and should run more rear bias. Some modern cars have proportioning valve indexed to the rear suspension load which atomically increases rear break bias with weight.
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