bias valve

[fxgt race]

Put new wilwood brakes on rear of the race car and took it to puke,was hope they wouldnt lock up but they did,I Have a bias valve to put in the rear line, Do i need to remove the factory bias valve.

[Rick]

Yes. I managed to put my wilwood valve in place of the factory one.

[TRD Man]

No, I wouldn't.
Presumably you're installing the bias valve in an attempt to cure the problem that exists now i.e too much rear brake.
Assuming that the factory valve directs more bias to the front than the rear, by removing it you'll be negating most of the effectiveness of the adjustable valve.

[Adoom]

No, I wouldn't.
Presumably you're installing the bias valve in an attempt to cure the problem that exists now i.e too much rear brake.
Assuming that the factory valve directs more bias to the front than the rear, by removing it you'll be negating most of the effectiveness of the adjustable valve.

It doesnt really direct anything.
The adjustable valve reduces/restricts the pressure in the system(front/rear) it is installed in.

So in my system(KP Starlet), the master cylinder has two outlets. One goes to the front brakes, one goes to the rear. The line to the rear has the non-adjustable factory bias(restrictor) valve in it.
I changed all my brakes and the back drums would lock up early. Replace the factory valve with the adjustable valve, then wind down the pressure to the back until the back brakes don't lock up early.....

[Adoom]

From the willwood site:
WILWOOD PROPORITONING VALVES FEATURES:
Compact and lightweight forged billet aluminum construction has made Wilwood's proportioning valves the best available. Pressure adjustments range from 100-1000 PSI and provide for a maximum decrease of 57% in line pressure. This adjustment lets you fine tune the front to rear braking balance by proportionately decreasing the rear (or in some cases the front) brake line pressure. Can also be used to adjust individual front wheel braking in dirt track applications.

[Adoom]

Here is the info sheet
http://www.wilwood.com/Start/PDF/ds488.pdf

[Rick]

No, I wouldn't.
Presumably you're installing the bias valve in an attempt to cure the problem that exists now i.e too much rear brake.
Assuming that the factory valve directs more bias to the front than the rear, by removing it you'll be negating most of the effectiveness of the adjustable valve.

The factory bias valve on my car only affects the rear brakes. Not sure if all cars are like this but all the cars I have worked on have the same setup.

[fxgt race]

Can somebody tell me which lines of the booster do what, At the front off the booster one goes to the right front brake and tees off to the bias valve,where does this one go,front or back brakes. The hard line that comes off the booster closer to the firewall goes down to the bias valve also,what does this on do.

I want it were i can reach the valve as i have a race meeting in three weeks and will have to test it the day before and will have to adjust at on the day to get it right.

Can I tee both rear lines together run it through the floor to the wilwood bias valve back down under the car and tee it back into the two lines to the rear brakes,do you see a problem running two lines into 1 and back to 2 again.

[TRD Man]

Whether you have a dual circuit system with a reducing valve in the rear or a system with a bias valve directing different pressure front & rear, the effect is the same. The bias valve limits the pressure to the rear brakes relative to the front.

I don't know what the factory ratio is or by what amount the valve reduces pressure but let's for simplicity sake say it's 57%.
In that case removing it would negate any effect the Wilwood bias valve would have. When in it's most closed position the result would be exactly the same as now and any measure of opening would be proportionately worse.

Presumably the factory reduction is somewhere between 1% & 57% but given that there is already an issue with too much rear brake the question is ~ is the difference between whatever it is currently and 57% going to cure it?
The chances are that if it does, it will do so with the adjustable valve on it's fully closed setting.
And what is the benefit of having an adjustable valve that remains permanently on one extremity and with which you cannot adjust anything?

We're talking about a FWD car here, are we not? No weight over the rear wheels, no engine braking effect.

On my FWD Corolla rally car we ran braided lines from master cylinder to all 4 calipers with a Wilwood bias valve in the rear line. We had far too much rear and even on it's fully closed position.

The cure was to put a reducing valve in the line and after doing so we had full adjustability. Fully open and we locked up the rear, fully closed and we locked up the front, and in between we had full adjustability.

[fxgt race]

so i should tee the valve in the line off the master cylinder before the factory bias valve that then goes off into two for the rear brakes(went i work out which one off the master cylinder it is).

I understand that if i only run the new bias valve that the 57% that it reduces the pressure may not be enought to stop the rears from locking up and will need to run it in conjuction with the factory valve.

[matt dunn]

Being FWD it may be split diagonal braking, not front rear.

If so you will need to re-plumb the whole system.

Start at one of the rear brake line and trace where it goes,
If it goes to the opposite front wheel it is split diagonal.

If it goes to the other rear it is not.

In a split diagonal system there is nowhere in the system you can fit it to affect both rears.

[fxgt race]

thats the tricky part, 2 lines from the master cylinder go into the factor bias valve,1 goes to LF and 2 head off to the rears, which one goes to which inside this valve is what i will have to find out.

Got yourself a little write upin nz racer mag i see

[matt dunn]

thats the tricky part, 2 lines from the master cylinder go into the factor bias valve,1 goes to LF and 2 head off to the rears, which one goes to which inside this valve is what i will have to find out.

Well the fact that there is two lines to the rear means that it is split diagonal.

So it's a double bias valve standard.
Need to re-plumb the system and remove the std valve.

[fxgt race]

yes the bias has two valves in it

[TRD Man]

Matt's correct. Looking at the book it is a split system, which is why we replaced the whole lot with braided line.

The proportioning valve reduces pressure to the rear by 51.5% which reinforces what I was saying earlier about the need to retain the valve.

If wanting to use as much of the std system as possible, this what I'd do.

If you've got a load sensing proportioning valve in the rear, take it off & bin it. Tee junction the two lines together and run one line back to the Wilwood valve mounted where you can reach it.

In the front, find the line that runs from the proportioning valve, on the firewall, to the left front wheel. The line exiting right next to it, running to the rear, will be the one on the same circuit. Close it off.

Run the other rearward line into the front of the Wilwood valve.

Now you need to swap over the two lines coming from the master cylinder into the proportioning valve. One will be too long but should be able to be shortened to fit. The other will be too short and you'll have to make up a new one.

[Bazda]

I played with this on mine a while ago as I installed MR2 rear brakes to my levin.
Which did not work out at all. Kept locking the rear with those calipers.

I tried by passing the stock valve completly and re did the whole system. I also tried using the stock valve with the wilwood adjustment and 2 extra valves from a BMW E30. Still no luck with the MR2 calipers.

I just went back to stock. Ideally I could do with a tiny tiny bit more rears.

When you say it blocks 51.5% to the rear. I thought it was alot more. My rears hardly work. I would say mine are only working 10-20% max. Enough to just settle the car.

You will need to replumb the whole system to get it to work correctly.
I found that the rears are fine on mine and its not worth the hastle

[Dunny]

Maybe a change of pads in the rear would help your problem, maybe go down one or two levels in pad 'bite'?

[Boost_4_Life]

yea ya dont need such an agressive pad on the rear, will only make it worse. case in point my starlet we have tried agressive pads all round, could not stop the rears locking, even with bias adjustment. so had to back off on the pad. mind you rears locking wasnt such a bad thing for me anyway

[TRD Man]

When you say it blocks 51.5% to the rear. I thought it was alot more.

According to manual pressure from master cylinder is 80 kg/m3 and pressure exiting proportioning valve to rear is 39 kg/m3

I found that the rears are fine on mine and its not worth the hastle

I always thought Corolla brakes were quite adequate so I agree with you here. Certainly most AE82 & AE92 rally cars ran with std brakes.
Our car ran S3 Celica motor/box, hubs and brakes which is why we played around with them.

[IH8TEC]

I've been through about 5 sets of front pads and still on the same set of std toyota back pads in factory callipers, they are about 1/4 - 1/2 worn,

the rears are hardly touched.