Z4M long brake pedal travel

[jpeeters]

Hi all,

I'm having an issue with my brakes on my Z4M and hope someone will be able to provide advice.

When I bought my Z4MC with 45k miles on the clock I alread felt a soft brake pedal. The previous owner just replaced brake pads and discs (both OEM) and I thought it would be air in the lines causing this soft pedal feel.

Upon my request my indie (very experienced!) deleted the CDV and replaced the brake pads with EBC yellow, installed steel brake lines and replaced the oil with ATE blue dot 5 (high temperature resistant oil). During the CDV delete all oil has drained from the system. The dealer then filled it up again with the ATE blue and bled the oil at the 4 wheels. After the oil change and bleeding procedure I could't engage first gear anymore - we had to bleed the gearbox(?) using the pedal pumping method.

This pad/oil change/bleed procedure didn't solve the mushy pedal feel. I ran in the pads according to EBC's procedure and while brake power was ok, pedal feel didn't improve. I did 3-4 sessions at the Nurburgring and some daily commuting (about 5k miles in total) before the rear pads were completely gone (didn't really struck me then).

Back to the indie last week to replace the EBC's with Pagid RS14 front and RS29 rear. They bled the brakes once more and found out there was a little bit of air in the system front left. No improvement though on the brake pedal travel, so I started to investigate this in more detail.

Facts:

• brakes usually only "bite" when level with the accelerator (the latter untouched), while my 320 touring already provides stopping power 1/2-1 inch earlier. I've test driven a couple of other cars and they all engage the brakes with a shorter pedal travel then mine, and they are +/- at full braking power when brake pedal is level to accelerator pedal.
• sometimes the brakes "bite" earlier, the behavior isn't consistent
• with the engine switched off I can pump the brakes and they remain hard
• rear EBC pads worn out very rapidly, while the front pads were still in almost new condition

Potential issues I've been thinking about:

• air in the ABS modulator/pump
• air in master brake cylinder
• broken master brake cylinder
• broken DSC pressure sensors (source of rear pad wear?)
• broken DSC pre-charge pump
• leak in vacuum hose to the booster

Since replacing all those potential problem sources will be quite expensive I'm wondering if someone could advice where to start first. I'm thinking about bleeding the ABS modulator/pump as a first step, followed by doing a pressure test of the master brake cylinder secondly.

Any other opinions?

[jpeeters]

In the meantime my indy performed the ABS modulator / pump bleeding procedure and it improved things significantly. The pedal travel is still longer then I would like, but at least the feel is consistent among a few Spa and Nurburgring laps.

The long brake travel is normal on the E46 M3 / Z4M, given the architecture of the brake system. I've compared with other owners and the feeling is similar in their cars. Why did BMW choose for a 1 piston setup in a sportscar . Anyway, seems like they learned their lesson in the new M3/M4...

[jpeeters]

One additional thing I noticed is that under heavy braking the pads wear unevenly. I've ordered two caliper bushing upgrade kits (http://www.turnermotorsport.com/p-4118- ... e-kit.aspx) - hopefully this will fix this issue.

[barryb97]

Same issue with my 06 Z4 M Coupe. Flushed the fluid 3 times, put in the bushing kit and new pads helped a quite a bit. Makes it difficult to heel/toe during heavy braking. We'll see if it comes back once the pads get a little worn.