Brake proportioning valves.

[benebob]

Our racer suffers from too much rear braking ability so naturally since I know nothing except to drive like I stole it and Steve McQueen is after me I have a tendancy to lock up the rears. Did it at least 3 times yesterday. One that I could smell tire inside the cockpit. This is even with crappy advance pads in the rear and axis up front!

Anybody have experience with proportioning valves? I'm guessing that we'd want 2 so that we can maintain the diagonal braking set up for safety right? Do you just cut the line flare it out and put it in? Any brand model that you'd recommend or wouldn't?

[dynomatt]

Do you still run your standard ABS system?

For my car, down the track I intend to install a pedal box. This gives you individual master cylinders for front and rear, then a balance bar which changes the balance between front to rear via a red knob you mount on the dash. This gives you infinite adjustment.

As to the diagonal setting, again, it's a racer, so not important. You want control, and pedal feel. Getting rid of the booster is actually a good thing to. Whilst it makes the pedal effort greater, the feel through the pedal is never compromised by a vacuum problem.

From a rallying perspective, rear bias is actually a good thing. It helps when you're in a blind corner that tightens, so that the end comes round rather than understeering off.

If you want to reduce rear bias, a simple inline bias valve would work. Does the ABS mean that the rears have a single line to the back brakes, or are they a dual line from teh ABS pump?

You should consider a hydraulic handbrake too...that would get the car turning on a dime in the tight stuff.

Matt

[Hocrest]

No, we got rid of the ABS, and just have "T's" in place, but it is still set up diagonally.

I was thinking to repipe it and lose the diagonal set up and just do a single proportioning valve between the front and rear.

[dynomatt]

Yep, I would remove the diagonal.

If you've got the pipe bending/flaring equipment going, consider then running the rear as a single line system through the cabin to the valve, then from the valve to a t-piece out to the rears.

A hydraulic handbrake would then go before the valve if you decided to do that too. Get's rid of all the cables etc.

Matt

[benebob]

Pretty sure the diag. brake set up needs to stay per GSR rules. I remember seeing that if a car came with it, you needed to keep it. Your set up seems a little pricey and heavy to me. Weight is always an issue.

As for the handbrake. We can do away with it entirely which I'm wondering how much weight we'd save clearing out that rear drum.

[dynomatt]

What sort of racing do you guys do?

A proportioning valve can be had for $80USD or probably less and weighs about 200grams.

If you have to run diagonals, then in order to retain that, you'd need two valves, one per rear line.

Not sure how that's pricey or heavy.

Matt

[svxfiles]

Originally Posted by benebob

Pretty sure the diag. brake set up needs to stay per GSR rules. I remember seeing that if a car came with it, you needed to keep it. Your set up seems a little pricey and heavy to me. Weight is always an issue.

As for the handbrake. We can do away with it entirely which I'm wondering how much weight we'd save clearing out that rear drum.

AND the heat shields!
And PB cables,
And hand brake,

[benebob]

Originally Posted by svxfiles

AND the heat shields!
And PB cables,
And hand brake,

What heat shields? I think they've been gone for some time now.

[benebob]

Originally Posted by dynomatt

What sort of racing do you guys do?

A proportioning valve can be had for $80USD or probably less and weighs about 200grams.

If you have to run diagonals, then in order to retain that, you'd need two valves, one per rear line.

Not sure how that's pricey or heavy.

Matt

Its an autoxer now but will as soon as the cage is in and fire suits bought be a hill climber which would fall under the same rule catagory as SCCA club racing.

Yeah I was pretty sure we'd need two to remain diag.

[Beav]

Why not use the brakes to hang the butt out and the gas to straighten it up?

Prop valves are available almost everywhere. Get an adjustable one and mount it where the driver can reach it. And ditch the diag.

[dynomatt]

Beav,

That's what I was trying to say...rear bias is good in rallying!!

Sounds like you can't do it easily then, and the only other cheaper suggestion is to get crappy pads for the rear, or more aggressive ones for the front. Let the pad compounds give you the bias. For example, standard pads in the rear (yes they'll be smoking and faded) vs something like Ferodo DS3000's in the front...that would get you heaps of front bias back...maybe too much.

But you get the picture.

Matt

[benebob]

The rear won't break out it simply locks up (which ruins tires in a few tries on pavement). Already have crappy brakes in the rear, good up front.

[SVXRide]

Ben,
You might want to take a look at this....

http://www.pegasusautoracing.com/pro...p?Product=3528

-Bill

[dynomatt]

that's exactly what I was talking about, I have used the Willwood version both are the same.

However, if he's running a dual rear system, then they need two.

I'm curious as to the rules you run under...have you got any websites that point to the regulations?

Thanks,
Matt

[benebob]

Originally Posted by dynomatt

that's exactly what I was talking about, I have used the Willwood version both are the same.

However, if he's running a dual rear system, then they need two.

I'm curious as to the rules you run under...have you got any websites that point to the regulations?

Thanks,
Matt

Solo (autox rules) are at www.scca.org and online
Club racing you have to buy the book still I think.