I have a Wilwood Bias Valve like this one in-line to my rear brakes:


Wilwood bias valve

I'm just head scratching a bit as to which way is which. It says 'Decrease' on the handle with an arrow – does this mean decrease line pressure, i.e. reduce the rear braking , or does it mean decrease the restriction in the line, i.e. increase the rear braking?
Reading a few threads on here, I probably won't need it anyway, but seeming as it's already fitted, I want to set it to leave the pressure unaffected – I can always then change it if the rears lock up first.

Told you it was a dumb question

Oh, and before anyone asks, it's in the engine bay, so there is no way you can adjust it whilst driving.

I have used one like that and with the handle fully bent over the rear brakes were locked.

Wherever you put it it will fail assuming you haven't passed IVA yet.

quote:

---

Originally posted by prawnabie
I have used one like that and with the handle fully bent over the rear brakes were locked.

Wherever you put it it will fail assuming you haven't passed IVA yet.

---

It should'nt lock the brakes totally which ever way you fit it its bias valve not a line lock..

Mines the screw type and decrease means decreases the pressure to the rear brakes ie less braking, and its also a willwood item..

Iva dont allow adjustable brake valves if i remember correctly, but as you cant reach yours from inside im not 100% sure if yours is ok or not...

Rob

quote:

---

Originally posted by neo2
It should'nt lock the brakes totally which ever way you fit it its bias valve not a line lock..

Mines the screw type and decrease means decreases the pressure to the rear brakes ie less braking, and its also a willwood item..

Iva dont allow adjustable brake valves if i remember correctly, but as you cant reach yours from inside im not 100% sure if yours is ok or not...

Rob

---

www.wilwood.com/PDF/DataSheets/ds489.pdf

IVA requires the fronts to lock before the rears, if you don't know what happens without the bias lever, how can you set up the lever?
You could fit it and pin it but still need to address any problems at IVA.
Perhaps using locking wire would convince IVA man that it permanently fixed but you could at IVA cut the wire reposition lever and rewire if you failed on bias

[Edited on 15/8/10 by snapper]

Thanks for the replies.
I simply don't have any way of testing what wheels will lock first, before I get it on the road - what have other people done to set up brake balance before the test? I was hoping to do as Snapper says and alter it at the test if it fails, but if this isn't an option I'm stuffed

quote:

---

Originally posted by bilbo
Thanks for the replies.
I simply don't have any way of testing what wheels will lock first, before I get it on the road -

---

quote:

---

Originally posted by interestedparty

quote:

---

Originally posted by bilbo
Thanks for the replies.
I simply don't have any way of testing what wheels will lock first, before I get it on the road -

---

You don't have any way of testing that after either Im afraid!

Thing is at IVA they test braking effort at several different pedal presuures, so even a MOT station cant test that, nor would driving it on a road, unless you had a road with lots of different surfaces.

If a car was being driven on a slippery road (maybe slightly oily wet road, for instance) and the rears were more efficient at LOW pedal pressure (which they might well be, even though less efficient at full pressure) then the car would spin if the driver braked gently in a curve.


The only answer is to try it on full pedal pressure (at MOT for instance, or on a private road, or even a gravel drive) and go woth your best guess, and go to the IVA. Your chance of passing first time is low anyway, so budget £90 for a retest .

---

Another factor to consider is bedding in the pads & discs makes a LOT of difference to braking performance and balance. When my car was tested (SVA) everything was brand spanking new and the tester allowed me to do a few laps of their 'circuit' to try and get a bit of heat into the brakes. Needless to say it was a bit of a gamble and I was gobsmacked to pass - the car had never been run before the test! The force needed on the brake pedal was actually painful

Later, with a few miles on the clock, the braking performance was vastly different from the test. I needed to reset the bias bar to stop the fronts locking up. Sometimes the test parameters don't make any sense .....

Good point on the bedding in. I'd planned to drive the car to IVA to bed everything in, but then that messes up any tests I do on my drive.
I have to say, I'm bricking it a little re IVA before I've even got a date.
After 4 years of build, I'm finally almost there and I'm getting paranoid about everything.
Doesn't help as well that I started building to SVA regs, then had to rethink stuff when IVA came in

[Edited on 15/8/10 by bilbo]

Bear in mind therre are pleenty of our cars out there without adjustable bias pedals and without an in line device like this that are working perfectly well.
I'd say if in doubt leave it out

Bias valves are not allowed for IVA, doesn't matter if it's locked.

quote:

---

Note 4: Hydraulic valves that only operate automatically and react to vehicle loading or braking forces are permitted (Load Sensing and Gravity valves) Manually adjusted valves (other than to permit presetting the automatic function of a valve) are not permitted to be fitted even if they are rendered un-adjustable.

---

quote:

---

Originally posted by matt_claydon
Bias valves are not allowed for IVA, doesn't matter if it's locked.

quote:

---

Note 4: Hydraulic valves that only operate automatically and react to vehicle loading or braking forces are permitted (Load Sensing and Gravity valves) Manually adjusted valves (other than to permit presetting the automatic function of a valve) are not permitted to be fitted even if they are rendered un-adjustable.

---

---

Hi

If you get completely stuck with whats happening at the calipers with differing pedal pressures and fancy a trip to Brum. I can run our brake bias gauges on the car. It measures line pressure at the calipers giving percentage or actual line pressure readings.

Cheers Matt