roadracer380

I would like to install an adjustable proportioning valve on my FD because of the front brakes engage the ABS way too soon. My question is should I add the proportioning valve to the front brake line or should I remove the stock proportioning valve from the rear and add the adjustable there? Is that even possible? my fear of adding it to the front would be increasing the pedal effort. If I added it to the rear will I be able to adjust out enough to better proportion the system? Through my brief research I have only seen write ups of adding it to the front when retaining the ABS system. Is that required?

LargeOrangeFont

iTrader: (7)

I would not put a prop valve on the front, that is a bad idea. What have you done to the braking system if anything?

What tires do you run? Have you tried wider or stickier front tires?

roadracer380

So far I have done nothing to the brakes. My car makes 1000 whp so I plan to do a front brake upgrade soon but it's still needs more front bias as it sits. My tires are 285 30 18 Square. Thanks for your reply

roadracer380

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

This link is where I got the idea of putting the proportioning valve on the front brakes

LargeOrangeFont

iTrader: (7)

If you are into ABS on the front wheels you need more rear brake bias. You could do that by putting a prop valve on the rear brake circuit.

If you are locking the wheels and getting into ABS now, bigger brakes are not going to help you.

You may need to remove ABS, and upgrade the brakes properly.

Modifying you brakes so you need a prop valve on the front brake circuit is not a good idea. You don't want to lower the clamping capacity of the front brakes. If you size the caliper pistons properly you do not have to go through these goofy exercises to get the bias back in line.

roadracer380

That is good information, thank you. Hypothetically speaking, if the stock rear proportioning valve was completely removed would the rear brakes then overpower the front brakes? I understand a proportioning valve can only create a restriction and I fear if I add big brakes to the front will I be forced to modify the rear brakes to compensate? or will I be able to adjust it out with a proportion valve on the rear?

LargeOrangeFont

iTrader: (7)

If you put bigger brakes on the front put a prop valve on the rear and dial rear brake out until the fronts lock just before the rears.

You need to know what you are putting on the front. You need to keep a similar piston area to stock and you will be able to keep the brake bias balanced with a prop valve on the rear. You can screw it up with improperly sized pistons such that a prop valve won't be enough to help you.

roadracer380

http://www.wilwood.com/BrakeKits/BrakeKitsProdFront.aspx?itemno=140-11964-DR&year=1993&make=Mazda&model=RX-7&option=All

Great advice. How do you feel about this Wilwood 14" kit?

LargeOrangeFont

iTrader: (7)

Blue TII did a review of that kit in this subforum.

https://www.rx7club.com/suspension-w...eview-1039256/

ZDan

You should be able to get a big brake kit that maintains proper front/rear bias. Pretty sure StopTech offers bigger and smaller piston options for the front brakes. Smaller piston option works with stock rears, larger piston option works with larger-diameter '99+ rear brakes.

I haven't had any bias issues with Stoptech ST40 fronts and 99+ rears on my FD. Except for one time, with new CarboTech XP10s I got rear bias (spooky!) for the first couple of laps... After bedding, no problemo.

I recommend getting the factory setup to work properly over adding a prop valve. Proper system should work fine, and you can run different front/rear pads to fine-tune.

LargeOrangeFont

iTrader: (7)

I agree.

I do have a prop valve on my FC and it is working very well. You just need to use care when dialing it in on the track. I installed the prop valve because I have a Ronin Speedworks Mandeville front BBK, which added front brake bias, and needed to get the rear back in line.

All that said.. if you are getting into ABS now.. bigger brakes wont help you with that problem.

eage8

iTrader: (9)

I would go over your brake system first. I had a similar problem with my car and it turned out that one of the rear calipers was frozen and not doing much...

check your brake pads, if they're staggered or just crappy brand it won't help.

that being said, if you install a prop valve, remove the stock one and replace it with an adjustable one on the rear line. that's what I did to my autocross car. currently the valve is all the way open (50/50 front to back) but my car isn't a normal case (very very stiff with square 315 race slicks).

This is the kit I used on my FC:
Flyin' Miata : Chassis : Brakes : Complete adjustable brake proportioning kit

LargeOrangeFont

iTrader: (7)

I use the FM kit as well.

roadracer380

Currently my brake system is 100% stock write down to the rotors and pads (came with the car). The entire system has been rebuilt. I agree bigger front brakes will not help the bias situation, I would just like to improve braking capacity and adjust the rear from there. I would like to keep the stock diameter rear rotors for when I go drag racing to fit small wheels. I was also considering upgrading the rear calipers to an aftermarket 4piston, maybe I will try to size the caliper for improved bias. Thanks guys for leading me in the right direction. Does anybody have piston area specs for the stock rears?

chrismore

I am working through my custom brake setup while retaining the ABS and the content in this thread is helpful, but doesn't completely answer my related questions. I started a thread if anyone wants to contribute: https://www.rx7club.com/race-car-tec...issue-1164665/