Here is my setup and my problems.....

Master cylinder 1in bore 929 master
Front brakes Willwood 6 piston Calipers (M2 KIT) 13in rotors
Rear Brakes Brembo 4 piston, Lotus elise calipers on 13in rotors(made the kit myself, with help from a board member)
ABS deleted, the lines from the master are run direct one to the front and one to the back brakes.(obviously split to power both sides)

Here are the problems, Pedal feel great..... but my front brakes are overpowering the rear. Does the 929 master have a built in proportioning? or is my logic behind this wrong... The front kit from what I remember has 55cm2 and my rear calipers have 40cm2, so the rear should actually being grabbing harder then the front? Yes, or No? I am confused...

 

Not sure i can answer your question, you've changed so much. What did you do about an e-brake, nothing?

 

No E-brake.

 

Maybe I should change my Master back to stock, the proportioning might be better. Any ideas on it?

 

The only difference between stock and 929 that i'm aware of is that it pushes more fluid, and thus sets your pedal up better. I've never heard of it changing the proportioning on other setups. I'd suspect it has to do either with the way in which you rerouted the lines after ABS-delete, or the matching of those rear calipers to front.

 

The MC won't change the proportioning.

More piston area = more grabbing force for the same amount of pedal pressure. But comparing front and rear directly is not a very useful comparison. For one thing, you don't want the rears to grab as hard as the front.

See what other piston configurations are available for your rear calipers. Brembo might make the calipers with several bore sizes. The Wilwood NDL caliper I use on the rear is available with several different bore sizes (mine are 1.12" diameter).

Make sure you don't have a kinked hard line anywhere.

Do you have the same pad compound front and rear?

I would not use a proportioning valve on the front circuit. But people have used them to weaken the fronts.

-Max

 

I just did some quick piston area calcs (maybe sloppy, so double check them if you decide to rely on them as truth):

My AP5200 front calipers (2x1.5" + 2x1.65", I think)= ~50 cm^2
My Wilwood (4x1.12") = 25.4 cm^2
Stock rears (1x1.39", doubled since it floats) = 19.6 cm^2

My quick estimation leads me to believe that your rears should actually be overpowering your fronts.

-Max

 

Max, check out this link it may explain more... and BTW I am running HP+ pads all around.

http://www.swapcartech.com/forum/showthread.php?t=430

 

How are you assessing that the fronts are indeed overpowering the rears? They lock first? What size tires are you using F/R? How do the pad size/shaps between F/R compare?

 

Rear brakes still look like new, and yes rear lock first but under light braking they are not working. Tire sizes are 225/40/18 front and 275/35/18 rear. Pad shape,
not sure what you mean, they are the ones that fit. LOL
Did you read that link I put up.

 

Why don't you just get one of those adjustable bias proportioning valves and attach it to the front brake line coming out off the master. Then just keep reducing pressure to the fronts until you are happy with the bias set up.

But also one thing to consider is that you have upgraded the front brakes ability to clamp harder and better yet you did not upsize the foot print of the front tires (225). So that is also something to consider as well. That alone could also cause early front brake lock up.

 

I read the thread.

Rears locking first is dangerous.

I agree that your rears have too much area and will be hard or impossible to balance with a single master. Though maybe it will be okay when you get the dual masters. Use a larger master for the rear versus the front to reduce the pressure on the rear. For now, you must install a proportioning valve. I would do this before troubleshooting because it might fix your problem. Or undo the fix if you fix it first.

Install a proportioning valve in the rear circuit. Do not install one in the front circuit. Even when you get the dual masters going, you will still want a prop valve to give you good braking under both light and heavy braking.

Can you get the same rear calipers with smaller pistons? That might both fix your light and hard braking problems. Under light braking, less fluid will be required before the pads contact the rotor.

Another factor to consider is anti-knockback springs. These are springs behind the pistons that keep the pads close to the rotor (or even lightly rubbing on the rotor). The range of possibilities is that a caliper does not have them, or does have them in one stiffness or another. You might find that your front calipers have heavy anti-knockback springs and the rear calipers have no anti-knockback springs. That would cause the front brakes to grab first, since the pads will be riding closer to the rotor. Evening up the knockback behavior might even up the braking under light application.

I have never heard of using a residual pressure valve on disc brakes. They are common on drum brakes. But the theory makes sense and it just might fix your light braking problem.

Watch out if you try the four-port manifold to join the front and rear circuits. Doing that will defeat the failsafe in the event that you spring a leak. It might be worth swapping the lines to see if it changes anything, but I suspect the problem is somewhere else in the system.

I would look carefully at the brake lines. A kinked or flow-compromised line in the rear circuit would make them react slowly.

-Max

 

Max, thanks for all the advice, I will be working on it this weekend and I will report back on the progress...

If you want to read this thread, this is how it all started..

http://www.torquecentral.com/showthr...ghlight=brakes

 

I ended up joining the outlets coming from the Master into one and then T'd them off into two one front one rear, front direct to the brakes, rear to a prop valve. I will update tommorow, going for road test tonight and to the track tommorow. Will see what happens!

 

Went to the track, dialed in the rear brakes... and I am loving it! Nothing like driving fast and being able to scrub the speed as fast as you accelerate. Just got to learn the brakes better, learn the exact lock up point.

 

Sorry to revive an old thread, but isn't this pretty unsafe?

It was my understand that the stock brake system operates on two separate hydraulic circuits (divided into front and rear), so if there is a failure on one of the circuits, the other side will still work.

Am I wrong in my thinking?