help with adjustable brake proportion valve

[Dreco]

Hello all. I purchased an adjustable proportioning valve for use with my rear disc conversion on my 240Z. According to the instructions, increasing the valve, increases the pressure to the rear brakes. My question is: does restricting the flow increase pressure?? I blew through the "IN" side while turning the valve. The more I turned in the "increase" direction, the harder it was to blow through it..... can anyone explain this to me??

[Daniel]

The valves job is to try to ensure the rear wheels lock before the front.If you've ever had the front lock first on a motorcycle you understand oh too well.Increase pressure is somewhat false.It holds pressure is more correct.Most disc I believe are 5lb. For drum they hold 10 lb. of pressure on the rear brakes.That way when you hit the brakes ,the rear brake is already 5 lb(or X amount with the adjustable unit) of pressure ahead of the front. Therefore it's pressure is alway alittle greater than the front for the first split second each time you hit the brake pedal.

[Phred]

Important!

Do not set up your brake system to lock the rears first. I have about twenty years experence setting up race and street brakes.

If you lock the rears first, the rear of the car will try to pass the front, and bad things will happen. If the fronts lock first, the car goes straight. To recover, you simply release pedal pressure, regain traction and drive away. Cars are cars, not motorcycles.

Before you kill yourself, go to www.willwood.com or call them at

(805) 388-1188 for info.

Phred

[2ManyZs]

Stock proportioning valve put somewhere in the neighborhood of 75-85% of the braking force to the front brakes so that the rear don't lock and the driver loses control.

The main reason for using an adjustable proportioning valve is the be able to adjust the brake system so that the rears do more of the braking, but not the point of locking up. This will keep the fronts from overheating in competition as they will not be doing the majority of the braking. You adjust the proportioning valve while using the brakes, up to the point the rears do lock up, and then back it off slowly until the rears no longer lock up during braking.

The valve itself only restricts the line pressure to the rear brakes by limiting the volume of fluid. It does nothing to limit the pressure in the lines per se, as that is limited by the pressure being exerted on the master cylinder and that is what determines the amount of fluid and pressure in the lines.

[Daniel]

Phred thanks for the correction.After review I find I was incorrect in my understanding of its function.I think I was 180degrees off.It doesn't hold pressure it decreases the pressure.Thats why when he "increased pressure" it reduced the flow to the rear wheels.Am I correct now? Sorry for the incorrect data. Thanks for the save Phred. If you don't make mistakes you don't learn. Daniel

[2ManyZs]

And don't bother going to the willwood.com address, all it says is willwood.com is for sale.???

[Phred]

2ManyZs

Sorry didn't I provide the complete address.

http://www.precisionbrakescompany.com/willwood_overture.html

I just keyed it up and got the complete site.

Wonder whats up with the for sale bit? I suppose the next time I place an order, it'll be like Datsun-NLA!

Phred

[2ManyZs]

Darned if I know Phred, either the whole business is up for sale, or more likely just the domain name?

Doesn't matter, I'm on a strict budget.... can't afford those high dollar binders......

[Dreco]

I talked to a friend of mine and he explained to me that the reason the pressure increases when you close the valve is because your forcing the same amount of fluid through a smaller hole. Like holding your thumb over the opening of a garden hose. The reason I got the adjustable valve is because I thought the stock valve ( being set up for drums ), would create too much pressure for rotors; ergo, the rear brakes would lock up to early. Plus, I have the toyota four piston calipers on the front. After putting on rear disc brakes, I figured I needed something adjustible to balance everything. So your saying, if the rear locks up first, just back off the valve until the front brakes lock up??

[Walter Moore]

By all means you want the front wheels to lock before the rear wheels.

My old '72 Pinto always locked the rear wheels first (until I started running the rear tires 10PSI underinflated...) and every time that I made a panic stop I wound up facing backward...:stupid:

Driving that car was like hitting myself in the head with a hammer, it felt SO GOOD when I quit!

But at least even now, 22 years after it died, I can still feel a skid starting WAY before I need to correct for it...