Poorvette Racing

Guys,

I have a 99 FRC dedicated road race car and am installing Stoptech ST-40 fronts in the front and C5 fronts in the rear. For anyone who has experience with a similar setup, did you need to upgrade your Master Cylinder? How was Bias and pedal feel?

andy3101

You need a rear inline brake proportioning valve. Then it's trial and error to get the balance right. Call Jeff Ritter at Essex or Todd at TCE as those two guys I found to know the most about brakes than anyone I know. Doug Rippie comes to mind also.

I am running Jeff's AP endurance fronts with c5 fronts on the rear and paid a pro shop/driver to set the car up and brakes was the biggest challenge. (My car is a 2002 z06). I think the MC setup was changed right around 99/2000 on the corvettes but not 100 percent sure.

CP Thunder

We had the Wilwood SL6Rs with the C5 fronts on the rear and stock MC. ABS worked fine but the pedal feel was never what she thought was optimum. Always had a soft pedal regardless of bleeding and new pads.

flash911

When you say set up and brakes were the biggest challenge, are you referring to installing an in line prop valve and then dialing it in or were there issues as well? Just want to understand as I'm just about to start on this myself.

andy3101

Setting up the balance. The rear brakes will over power the front brakes as you will have equal piston area front to rear. The piston area of the factory rears are close to half of the front. Keeping brake like pressure equal to factory will net double the braking force to the rear compared to factory. The inline prop valve will limit pressure sent to rears to help get the car balanced but the adjustments to get the balance right is trial and error and if you have abs still in the car it will be harder to set the balance cause the abs will keep kicking in not letting the rears lock up.

CP is correct. Pedal is longer due to piston area is larger than factory so the calipers take more fluid... I don't mind it but it does take some getting used to.

And if your abs every gives out on you and you don't have the prop valve set correctly you will end up with the rear of the car catching up to the front real fast.

I don't run abs in my car anymore after an abs/active handling issue caused me some trouble.

flash911

That was a great reply Andy, and thank you. Do you know what the piston area is on the AP Endurance is and if it matches factory front to rear piston area? Essex said it would work fine w factory rears.

andy3101

PM sent

z06801

I run a big Brembo kit up front and c5 fronts in rear, I went with the Doug Rippie master, perfect pedal

CP Thunder

We run the AP T1 fronts now and stock rears again still with stock MC. Works great and rock solid pedal feel......

gunluvS14

lazy question from me, I'm sure the answer is avaliable.
what is the OE master cylinder piston size, and what's the piston size for Doug Rippie MC?
i'm trying to do some brake force bias math.

96CollectorSport

The early cars (97 - 00) are easier to set-up bias wise than the later cars (01-04) because the later cars have dynamic rear proportioning (DRP) which means the bias is controlled by the brake control module. So I can see why it would take some time to dial things in on a later car.

On an early car you could remove the stock bias valve assembly and install an adjustable bias valve (the Wilwood one is popular, but I have seen a few go bad) then dial back the pressure in the rear until it comes out about right.

The two ways I can think to do this would be:
#1 Check it manually with a pressure gauge like this:



If you choose the right one it will have the correct M10 x 1.00 thread pitch to screw right into the stock brake caliper bleeder opening.

Then adjust rear braking force from there:
All other variables being equal, a stock front calipers hydraulic pressure with 80 lbs of pedal force is around 2600 psi
Again all other variables being equal a stock rear calipers pressure with the same 80 lbs of pedal force around 1630 psi
(Note: these won't be the numbers you see on the gauge - without the car running you will probably see closer to 600 psi - but all you care about is the percentage of the initial number)

So you would want to limit the rear by roughly 40% (37.3% actual)

Install all components - have the bias valve turned full open and check pressure front and rear. Once you have a baseline subtract the 40% and you know where you need to shoot for. (If initial pressure is 600 psi front and rear then shoot for 360 psi in the rear)

Method #2 is less accurate but would probably get you in the ballpark - put all components on the car set bias **** to full open, pull the ABS fuse, go out into a parking lot with a friend and have him watch which tires lock up first front or rear - keep adjusting until it looks like they are locking up at about the same time then go another 1/4 turn, put ABS fuse in and give it a try.

flash911

Man this thread delivers! Thanks all, and thanks Andy for the PM. I am going to run the stock c5z rear first and see how that works out.

franman69

Great stuff... I'm eyeing the AP Racing Sprint setup for my C6 front.. I was wondering about the Factory fronts on the rear. makes sense now that I understand the piston surface area part of the equation. I'll be sticking with factory rears.