Sparkystav trying to figure out how these work now!
i thought without looking that you sort of tapped between the lines (front and rear) and it released some across depending on how you had it set.

it appears not, but most go on about fitting to the rear line when you upgrade from drums to discs. i cant find a simple explaination

toxo What a bizarre choice of car and gearbox to turn into a race car! Out of interest do you know what weight reduction was done (presuambly as an attempt to fix the IS200s ridiculous weight distribution)?

As for adjustable brake bias valves, you have to use these on the MR2s when putting big front brakes on as you can easily upset the effectiveness of the brakes (they run a different bias setup to most cars as the weight's not all over the front wheels). As with the others though, I'm also not sure how they work with ABS as presumably the ABS controller is going to have thresholds set in it for how much to reduce pressure by etc in the case of a wheel locking.

lex2oos You mean, the problem is that only front wheels are locking?

toxo Probably the rears actually. You don't need to change the brake bias because you have disabled ABS - you change the brake bias because the calipers no longer match the factory bias. Disabling ABS just means you can change the bias more easily (plus ABS is evil).

To put it simply... if your total braking force was out of 100% then the bias would be set so that (for example) 60% fluid goes to the front brakes and 40% goes to the rear. It's done this way because under braking the weight all moves forwards so the car has larger calipers to the front to compensate. Under braking the front end becomes heavier and the rear end becomes much lighter (and therefore locks more easily) so it only needs smaller calipers. Ideally you reach a balance whereby the car doesn't nosedive (too much bias forwards) and it doesn't lock the rears up before the fronts (too much bias rearwards).

When you put bigger calipers on the front, your 60% of fluid going to the front brakes is no longer enough to bring them up to an effective amount of braking pressure before the 40% of fluid going to the rear has locked the rear brakes up. Locking rears is no use at all because you will lose the back end of the car - with locked up fronts you only lose steering.

But that's just fluid pressure - it becomes more complex when you start looking at caliper design. Just because a caliper is bigger doesn't mean it has a larger fluid capacity - many smaller pistons take less fluid to move than fewer larger pistons. I believe Stav's car suffers from this problem.

It's a complicated subject but you can rest assured that with replacement front calipers and a weight reduction program the factory bias will not be suitable for this car!

2tongues The simple explanation is the proportion valve acts like a time delay, for the rear drums.

toxo Drums?!