Race Car Rear Brakes Locking

[jdman 1 1 Cars]

I have built a race car 1.6 gti putting out 130 bhp 1.9 front hubs with new 1.9 calipers and rear 1.9 upgrade rear beam and calipers carbon lorraine rc6 front pads ds3000 rear pads. Braided lines all through the car, tillott bias and racing brake fluid. Standard servo and master cylinder both rear lines into one port on M/C the other blanked off the fronts into separate ports. The problem is on track hard braking im locking rears every corner cannot get the fronts to lock even with the bias fully forward, ive bled the system a number of times but cant stop the car. I was wondering if the car is diving under brakes and lifting the rear but i would assume the front should lock anyway.

[allanallen 528 2 Cars]

I think a good starting point would be to try some standard pads in the rear, ds3000 are a bit overkill in my opinion for a car that requires very little rear braking. That being said you should be able to lock the fronts once the pads have a little heat in them.

Daft question but have you got the bias valve fitted correctly?

[jdman 1 1 Cars]

I think a good starting point would be to try some standard pads in the rear, ds3000 are a bit overkill in my opinion for a car that requires very little rear braking. That being said you should be able to lock the fronts once the pads have a little heat in them.

Daft question but have you got the bias valve fitted correctly?

 

you might be right with the rear pads but if i stamp on the brakes i should be able to lock the fronts any way as for the bias it is working because if moved the lever to more rear and spun it straight away and had total rear brakes.

[B1ack_Mi16 67]

I have also split mine to have 1 line for rears for 1 circuit and the other circuit 2 lines, one for each front.

 

Mine also tends to lock the rears before the front unless the bias valve is really adjusted to a very low setting.

 

Didn't think it would affect it having a front/rear split, but maybe a diagnoal split might change the pressure a slight bit?

Not 100% how the master cylinder works from the top of my head.

 

Putting on larger front brakes will help the issue though.

[wicked 103 3 Cars]

What valve do you have (and how did you connect it)? Some valves have a limited attenuation of the pressure, so it could be that you valve cannot limit the pressure to the rears enough.
On the 1.6GTI there is a limiter in brake line under the hood. You could try to include that one as well on line to the rear?

[jdman 1 1 Cars]

I have also split mine to have 1 line for rears for 1 circuit and the other circuit 2 lines, one for each front.

 

Mine also tends to lock the rears before the front unless the bias valve is really adjusted to a very low setting.

 

Didn't think it would affect it having a front/rear split, but maybe a diagnoal split might change the pressure a slight bit?

Not 100% how the master cylinder works from the top of my head.

 

Putting on larger front brakes will help the issue though.

Im maxed out with the front brakes have 1.9 hubs and calipers with the discs and want to keep running the 14 inch rims i was thinking of putting a pedal box with separate master cylinders then i could could put a bigger bore for the front brakes

[jdman 1 1 Cars]

What valve do you have (and how did you connect it)? Some valves have a limited attenuation of the pressure, so it could be that you valve cannot limit the pressure to the rears enough.

On the 1.6GTI there is a limiter in brake line under the hood. You could try to include that one as well on line to the rear?

i have a tilton lever type brake bias im not sure what you mean how did i connect it there is only one line in and one out

[allanallen 528 2 Cars]

A 1600 uses a single rear line with a limiting valve in the pipe.

 

With a pedal box you'd fit a smaller cylinder to the front in your scenario, at the cost of a spongy pedal.

[petert 578]

Until recently I had a single line to the rear and Tilton screw type valve. It had to be 99% front to limit inside wheel lockup. Definitely change to standard pads. Insufficient droop will not help either. I got sick of flat spotting tyres so am changing to a pedal box. Maybe put a screw type in series with the lever type?

[SweetBadger 93]

I had exactly the same experience with my car last season.

 

Standard pads in rear, ds3000 up front (standard 1.9 calipers ) and the bias valve I installed had to be set at almost max to stop the n/s rear locking.

 

We have a pedal box and adjustable bias bar in the new car, takes a bit of getting used to the heavy pedal but doesn't lock the rears.

 

Edit: this was with a tilton screw type bias valve in place of the standard 1.6 one - single line to the rears

Edited March 31, 2016 by SweetBadger

[wicked 103 3 Cars]

i have a tilton lever type brake bias im not sure what you mean how did i connect it there is only one line in and one out

 

I meant; did you use one for the rear or one for each rear brake, did you remove the standard 1.6gti limiter or is it still in? Just to get the picture...

[jdman 1 1 Cars]

 

I meant; did you use one for the rear or one for each rear brake, did you remove the standard 1.6gti limiter or is it still in? Just to get the picture...

i just used a single line from the master cylinder and the origional limiter is gone