hi my car has a 355 by 32mm ap 6 pot cailiper kit on the front with ferodo ds2500 pads the rest of the syatem is standard except braided lines. my problem is that they dont seem to stop the car well enough the abs comes in very early and the car keeps going and the brakes get hot very quickly like there isnt enough pressure on them or there is an imbalance my question is what is the cause and cure? ie remove abs, fit bigger rear brakes to match and or a bigger master cylinder?
thanks

 

You need to upgrade the master cylinder, the 929 mc should work just fine.

http://www.rx7.org/Robinette/mastercylinder929.htm

 

Are you running a prop valve to bring bias back to OEM after installing the big fronts?

 

hi no prop valve i assumed maybe wrongly that the abs would compensate for the big fronts, when braking with the car from say 120 the abs comes in and the car doesnt really stop that well, when it does come to rest the brakes are smoking its like there isnt enough pressure on the pad from the caliper i had some older tyres on the car and thought maybe thats why the abs was coming in due to lack of grip but i now have toyo r888 (285/30/18) rear and (255/35/18) front so there is plenty of grip but it is still the same

have been looking at the 929 mc but would it improve delay the abs from coming in ?

 

+1 This is most likely your problem. I do not see how changing to a 929 master cylinder will help, all it will do is move more fluid so you would have less pedal travel, it will not fix the brake bias. Another option is to use two different types of brake pads one set on the fronts and a different set in the rear, this is another way to change the bias.


John

 

brake pads how can thay chage to bias also where would you instal the prop valve?

 

The friction coefficient/aggressiveness of the brake pad compound can affect the brake bias. ie run more extreme/track oriented pads in the rear to compensate for your monster front caliper pistons.

 

+1, by using a more aggressive pad in the rear, it will bring the bias back toward the rear a bit.

When was the last time you changed the fluid also what fluid are you using?

 

The best bet might be to get some larger rear rotors that'll help compensate, like this kit:

http://www.racingbrake.com/RX7_REAR_...2107-311-0.htm

I doubt you'll be able to overcome that differential with just pad compound.

 

First of all, how do you know you are getting the pads too hot? You should use thermopaint on the rotors and check the pad/rotor surface first (change the fluid to fresh, GOOD fluid while you are at it). It could be just the pad itself. The DS2500 is ok, but not that great of a race pad.

 

have you also thought that the tires on the car could be a bad option? while this doesnt really match your description, its still a possibility of bad braking

as for "they get hot like theres no pressure" Do you feel the pedal travel more than it should ? If thats the case, its a fluid/master cylinder issue.

Maybe you should explain more of your case

 

thanks for the replies i know the brakes are getting too hot as even on the road they fade and turn the discs blue and smoke to pads that is why i think more pressure is needed on the pad to contact the disc, im basically asking can the abs/mc restrict the fluid going to the fronts to keep its bias, as for tyres the more grip you have the less you need the abs surely?

 

"can the abs/mc restrict the fluid going to the fronts to keep its bias"

In short, no. The AP calipers have a larger fluid capacity than your OE calipers. Your existing proportioning valve doesn't know that you have larger calipers in the front, so it provides the same distribution of fluid as if you had OE calipers. Your problems are the result.


Try adding a proportioning valve, I'm certain that this will solve your problems.

 

thanks where should the prop valve be installed to the front or rear?

 

Sounds like bad pads and nothing else

 

Ive been running the AP 6 pots up front for a long time with the DS2500. I started off with stock rear breaks and the stock rear bias valve. Now the rear bias valve is set to reduce the break pressure on the rear breaks in % compared to the stock front calipers.

When u add a disk that is 60mm wider and 6 pot in the front the brake bias between the front and rear goes from 70/30 or what the stock bias is to somewhere around 95/5 to almost no break power in the rear. Now u are also running the ABS and the stock master pump. With the abs and master pump u will also not have enough force to push all the fluid to your brakes.

What i did was remove the stock rear bias and add a open y splitt in the rear. And add bias valve that is adjustable in the engine bay. Then i also removed the ABS as you don't want that.

Then u also would want the Mazda 929 master cylinder to get more force to the rear brakes.

And then add some good rear pads, and adjust the brake bias between front and rear. And your problem should be solved.

I never could get my AP racing front brakes to overheat on the track. And i did 30 minutes sessions at the time. Now i did add a full manual pedal system and a 4 pot big brak kit in the rear, and all i can say is, my car has never had so good brakes ever.

JT

 

One of the guys over here has used the FD specific 28mm AP kit and reported a shift in bias - believe there was a bit of playing around with the ride height at one end to get it to behave.

If you want to see where you're at, rough and ready

http://www.tceperformanceproducts.co...alculator.html

Standard master is .938", rear piston 1.374 and you can calculate the rest, as provided by Mazda, it is around 67/33.....