Brake Master Replacment - dual master cylinders?

[72dan]

I have Stoptech Trophy brakes 380 mm 6 piston up front and 355 mm 4 piston in the back.
It has always had too much front brake bias. I don't know the piston sizes and don't want to keep buying calipers to try and balance front to rear balance.

Secondly my brake pedal has a lot of travel it seems and is inconsistent. I think I need a new master but really want adjustable brake balance. At the track I get 600 F up front and 250 F out back.

Has anyone put in dual master cylinders or have any other ideas?

[Redd]

What makes u think you have too much front bias? If you are still running ABS/DSC brake bias is usually adjusted on the fly by the DSC unit.

As for inconsistent pedal travel, is it always long travel, or does it happen randomly especially after a series of turns? If the latter, it is probably pad knockback. Your ST Trophy calipers might be able to take knockback springs. I would give Zeckhausen a call, tell him your problems. He will be able to help you.

[72dan]

Originally Posted by Redd

What makes u think you have too much front bias? If you are still running ABS/DSC brake bias is usually adjusted on the fly by the DSC unit.

As for inconsistent pedal travel, is it always long travel, or does it happen randomly especially after a series of turns? If the latter, it is probably pad knockback. Your ST Trophy calipers might be able to take knockback springs. I would give Zeckhausen a call, tell him your problems. He will be able to help you.

Brake temps at the track. I’m a licensed pro racer, stopping distance too long, fronts too hot, need more rear bias to rotate the car.

[Redd]

Balance bias with more aggressive pads in the rear?

[Z K]

Stoptech calipers have a problem with pad knockback.

That said, try running the ABS bleed routine if you have soft pedal and long travel after a brake bleed.

[Ximian]

Regular ST60 piston sizes should be 36/30/30 mm. I'd imagine the Trophy ones are the same size. Next time your swapping pads, put your phone in there and look, the size is stamped on the pistons.

As far as consistency, the choice of brake pads, cooling of rotors, and weight of the car have a lot to do with it. The S65 generates a lot of heat, the DCT generates a lot of heat, and the mass of the car will really heat up the rotors.

I've had good experiences with the CarboTech XP20 pads on my ST60 for fade resistance, but it is very aggressive and will overheat your rotors, calipers, and brake fluid without an exceptional amount of cooling.

Take a look at titanium shims as well to decrease some of the heat from the rotors and pads transferring to the pistons, calipers, and brake fluid. On a 90-100F track day, I did long sessions and really pushing it chasing a 911T and McLaren and think I mostly destroyed my calipers because I've had an odd "steering wheel shake under braking" issue. I've ordered replacement calipers because that's the only part left that hasn't been replaced on the front axle that would cause the shaking (replaced pads, rotor rings/hats, all control arms, bushings, etc). So while the pads handled the extremely high heat, the rest of the braking system didn't - something to keep an eye on.

[tsk94]

You're almost certainly getting pad knockback with the STR kit causing the inconsistent pedal.
I don't know of anyone running a dual master setup on these cars to adjust bias as you'd lose ABS, and the MK60 ABS system is very good.

The simple solution would be to play with pad compounds front and rear. Or simply go to a more aggressive rear pad if you feel you have too much front bias at the moment as Redd suggested.

[Bmwdoubles_]

I run the Brembo 17z refreshes from Signature Werks. Here is my fix, as a standard brake bleed won’t fix the problem.

Run the brake bleed procedure using
ISTA.

Then run the brake DSC recalibration procedure on ISTA. This runs a clamping pressure test plan on all four calipers and determines max and minimum pressures. It makes the brake pedal higher on engagement and makes the brakes feel like when they were new.

Open ISTA and run the following:
Go to operations > Read out vehicle data > Complete identification

Vehicle management, service functions, chassis, and suspensions

Traction control, adjustment DSC unit, dsc unit adjustment > display > continue > yes


GL.

[Redd]

Originally Posted by Bmwdoubles_

I run the Brembo 17z refreshes from Signature Werks. Here is my fix, as a standard brake bleed won’t fix the problem.

Run the brake bleed procedure using
ISTA.

Then run the brake DSC recalibration procedure on ISTA. This runs a clamping pressure test plan on all four calipers and determines max and minimum pressures. It makes the brake pedal higher on engagement and makes the brakes feel like when they were new.

Open ISTA and run the following:
Go to operations > Read out vehicle data > Complete identification

Vehicle management, service functions, chassis, and suspensions

Traction control, adjustment DSC unit, dsc unit adjustment > display > continue > yes


GL.

Is there a need to do this procedure every time you change brake fluid?

[Tommysalami]

Originally Posted by Bmwdoubles_

I run the Brembo 17z refreshes from Signature Werks. Here is my fix, as a standard brake bleed won’t fix the problem.

Run the brake bleed procedure using
ISTA.

Then run the brake DSC recalibration procedure on ISTA. This runs a clamping pressure test plan on all four calipers and determines max and minimum pressures. It makes the brake pedal higher on engagement and makes the brakes feel like when they were new.

Open ISTA and run the following:
Go to operations > Read out vehicle data > Complete identification

Vehicle management, service functions, chassis, and suspensions

Traction control, adjustment DSC unit, dsc unit adjustment > display > continue > yes


GL.

Didn't know this was a thing. Gonna have to try it!

Do you have to do steering angle calibration procedure first?

[Bmwdoubles_]

No need to run the steering angle recalibration. Unless your wheel is off center and you threw that specific code.

[Bmwdoubles_]

Originally Posted by Redd

Is there a need to do this procedure every time you change brake fluid?

I would. It’s a simple procedure.