Most of my track experience is with Formula cars, super karts and go-karts. When I stumbled back into motorsports as an old man, this was the first time I had extensively driven a road car on a race track. I realized that the brakes on my 2006 BMW Z4M were very different than my Formula car experience. I hated them!

I installed an Essex AP Racing Big Brake Kit on the fronts. This made a massive difference over the stock brake setup. I personally think the brakes on the Z4M are the most inadequate aspect of the car in comparison to every other performance-impacting part. However, even with the Essex BBK I found the pedal feel lacking. Something else was wrong.

I tried new pads, using Ferodo DS2500s and then trying Ferodo DS 1.11 pads. I still was having issues with the brake pedal feel.

How does a master cylinder feel when it’s failing internally?

The brake pedal could feel spongy even when using track pads. It was as though the harder I pressed on the pedal, the more spongy it would feel, and the longer it would travel. Keep in mind the pedal pressure I am applying here is racing speed pressure, a bit like you are avoiding a baby stroller on the freeway.

I could apply a great deal of brake pressure and only intermittently trigger the ABS. I experienced rear brake lockup which is extremely unusual.

After some research and discussion with mechanics and experienced folks, it was suggested that the seals on my master cylinder may be going. It could be that the internal seals for the front system were leaking, this contributing to the rear brake lockup.

At one track day in 2020 a car in front of me braked much earlier than I expected. I had to stand on the brakes hard, and the pedal felt like it just kept going without triggering the ABS. It was a bit unnerving! That was the point I decided I had to do something…

What to do about it?

While this was likely unnoticeable for street driving, it was not going to work for track days. I decided to replace the master cylinder in pursuit of the best brake setup I can get for the radster.