Cheers!

When installing aftermarket brakes in a FC, or any other car i got a question.

When installing new rotors (possibly brembo xdrilled rotors) and HPS pads into an FC, same size rotors as stock i think for both rear and fronts, do i have to worry about incorrect proportioning of brakes after installation?

Since the stock master cylinder has its proportioning valve adjusted for factory components, if i were to start installing aftermarket hi performance brakes do i have to install an external proportioning valve and re do the proportioning?

And if yes, how do i reproportion the brakes?

Go out to an empty parking lot and slam on the brakes and keep seeing wheter fronts or rears lock first and adjust accordingly to get all 4 wheels to lock at the same time?

What if i have ABS?

Sorry for all the questions... thanx

Cheers!

So i'm assuming that everyone who has huge aftermarket brakes don't have this problem and i'm only just paranoid.

I asked this question a while back in the 2nd gen specific forum but got no answers either.

RETed

The rears do very little braking versus the fronts.&nbsp If you're paranoid about rear brake force, you can install your own proportioning valve and adjust to your liking.

Bigger brakes up front usually implies more braking force coming from the fronts.&nbsp This lets the rears brake a little less in terms of braking balance front to rear.&nbsp Sure, it's not optimized, but the key is to NOT have the rears lock up before the fronts...



-Ted

maxcooper

Brake bias is affected by a lot of things, including suspension tuning, rotor diameter, brake caliper piston sizes, pad compounds, how full your gas tank is, and so on. Stock systems are designed to lock the fronts first under all reasonably normal conditions. They do this by component selection rather than a brake proportioning valve.

When you upgrade the fronts and rears in about the same way, the bias will still be toward the front, which is best for safety. When you just do the fronts (like installing big front brakes), the bias will be more toward the front. Beefing up the rears will make the balance more neutral, which can result in shorter stopping distances, as you will be making better use of your four contact patches. But if you go too far and the rears lock first, you will spin and have a very dangerous car to drive.

Installing a proportioning valve can reduce the braking force of the end you install it for. So, if you installed a proportioning valve in the rear line, you can reduce rear bias. A brake proportioning valve cannot increase the rear bias in that scenario, however. You could install it on the front brakes instead, to move the bias toward the back, but having a proportioning valve in the front brake system is not something I would want on my car.

Many race cars have a seperate master cylinder for the front and rear brakes. The brake pedal pushes on a bar that is attached to both master cylinders. For equal pressure front and rear (which is just one factor in determining brake bias), the pedal will push on a point in the exact center of the bar. To adjust the bias toward the front, you can move the point toward the master cylinder for the front brakes. This is called a "balance bar" setup and it offers precise control over brake bias. You can even get a little remote **** to turn while driving (to adjust for fuel load, for instance) that will change the bias.

A brake proportioning valve is not as precise a device. It just reduces the pressure in the line you install it in.

The testing method you describe is just what people do. Go out to a parking lot (if you aren't at the track that weekend) and slam on the brakes. Make adjustments until the fronts lock just before the rears.

To an extent, ABS covers for sub-optimal bias. You mash the pedal with enough force to lock both ends up, and the ABS will make sure they don't lock. You end up with full braking force from all four contact patches.

Of course, this isn't always true because some ABS systems (like the one on the FD, for instance) has a single control channel for both rear wheels, so it will reduce braking force to both when either one starts to lock. I also just read about a 2-channel system that links the diagonal wheels. That sounds like a bad idea.

-Max

Cheers!

Thanx alot Max and Ted i really appriciate your explanations

RETed

I'm assuming that the original poster was going to remove the stock "proportioning valve", it's basically a restrictor valve in-line to the rears, on the vehicle (FC's have them, I assume FD's do too?) and replace with a aftermarket proportioning valve...



-Ted

maxcooper

I didn't know the stock systems had that. It seems weird to me that they would put that in there when you could do the same thing by choosing calipers with the "right" piston sizes. Maybe there is some final tuning that needs to happen anyway so they just use a valve/restictor and expect to tune it a bit.

-Max

Cheers!

i'm not acutally sure what i want to do yet... just researching before i start buying things... I might even put the Mazda 929 ABS master cyclinder in and run stainless lines everywhere... But i still need to do more research on this.

maxpesce

the Valve that you think is a PROPORTIONING valve may actually be a safety device that is intended to prevent the SUDDEN total loss of brake fluid if a brake line ruptures. If there is a Large differential in Brake line Pressure it uses a small ball to close off the circuit loosing pressure. I discovert the function of this device on my Fiat while trying to blead the rear brakes - if I opened the blead valve too much and pushed the pedal too quick it would close and prevent fluid flow to that rear wheels - thats one reason why you have to push the pedal Slowly when bleading the brakes.

RETed

I believe the Mazda factory service manual labels this "block" as a "proportining valve" and mentions it's basically a restrictor valve for the rear brakes.



-Ted