Brake Upgrade - Help Required

[Brian H]

I would like to upgrade the brakes on my Z and having been down this route before (and failed) I would like to understand what impact any possible upgrade will have. There seems to be plenty of people that throw BBK on 1.9s - 2.8s but doing this must affect the braking bias, front to rear!

Facts I know:-

I have a 2 port master cylinder (DSC) and the ports are as follows:-

• Port 1 = 23.81mm diameter
  Port 2 = 20.64mm diameter

There are two lengths listed for the master cylinder, these are as follows:-

• Length 1 = 35.9mm
  Length 2 = 116.4mm

Port 1 is for the front brake circuit and port 2 is for the rear brake circuit.

My brake calipers have the following Pistons:-

• front caliper single 54mm diameter piston
  Rear caliper single 36mm diameter piston

My front disc size is 300mm x 22mm

I have tried the following:-

E46 330ci front brake calipers and carriers with 325mm brake discs, these fit perfectly but the brake bias is not right, the calipers for the E46 have single 57mm Pistons.

Porsche 4 pot brake calipers and carrier, these would need some fettling to make physically fit and spacers on the front of the car so this is not an option.

Over to you gurus, how do I calculate the following:-

Relationship between the piston size in the brake master cylinder and the caliper piston size?
Current brake bias? I've tried to do this and got the figures to front 57% and rear 43% but not sure.

What are your thoughts

[deni2s]

What do I know is that stock brake bias is not perfect, but it is very safe. So it's ok to play with it around.

Make some search for brake bias adjuster valve, that might help you.

[Deano1712]

You can easily get too much front bias with a brake upgrade. You can fit the /M master cylinder as a direct swap. This drops the front pressure since diameter is 25.4mm. If this still leaves you too much front bias it may be possible to fit the rear /M caliper (or another BMW caliper with a bigger bore) to increase the rear brake torque. The /M rear is 40mm diameter.

[Brian H]

What do I know is that stock brake bias is not perfect, but it is very safe. So it's ok to play with it around.

Make some search for brake bias adjuster valve, that might help you.

This may be a solution, but not one I think I would be happy doing I would still like to keep my DSC system if possible and I think using a valve would crew up the DSC system, I could be wrong though!

You can easily get too much front bias with a brake upgrade. You can fit the /M master cylinder as a direct swap. This drops the front pressure since diameter is 25.4mm. If this still leaves you too much front bias it may be possible to fit the rear /M caliper (or another BMW caliper with a bigger bore) to increase the rear brake torque. The /M rear is 40mm diameter.

Thanks Mark, when I fitted the E46 calipers I had to pump the brake pedal to engage the front brakes properly (pushing the braking bias to the rear?). In my mind I had the same size master cylinder piston pushing a larger caliper piston therefore I had to double pump the pedal, I found my rear brakes would engage before the fronts as I had not changed anything in the rear brake circuit. If I had changed the rears at this point would this have evened the bias back out again?

[c_w]

I don't think I've seen anyone think about it in this detail, most people put the BBK on and find it fine!

One easy way to alter bias is to run different grade brake pads front and rear. Pagid or Carbone Lorraine run different grades with different friction ratings which allow you to do this.

[Brian H]

I don't think I've seen anyone think about it in this detail, most people put the BBK on and find it fine!

One easy way to alter bias is to run different grade brake pads front and rear. Pagid or Carbone Lorraine run different grades with different friction ratings which allow you to do this.

Hi Chris

I put bigger calipers (E46) on a while back and found I had to double pump the brake pedal to get the front pads to engage properly (when they did engage they were great), I went from a 54mm caliper piston on either side to a 57mm caliper piston and this was enough to cause an in balance in the system.

I spoke with APRacing the other day and they do a BBK kit that requires no modifications to the master cylinder, great I thought, the hard part is paying for the kit though it is £1550.00ex VAT.

Brian