Brake pedal issues.

[leaded]

Did anyone get any further finding a bigger BMW master cylinder for the alcon kits?

[The Gorilla]

Hi,

Having now driven a E46 M3
with full Alcon Brake kit the difference
in the initial Brake bite is very
noticeable, compared to the full AP,
even more so when you get both
sets really hot.

What could work for the Alcon set up is
to fit Brake residule valves in the hard lines
just before the flexi ones.

A residule valve will reduce the amount
a caliper piston backs off and should give
a much more responsive pedal bite on
initial pedal.

They maintain a higher line pressure which
should reduce pedal travel.

Will not alter anything else, but should
hopefully reduce pedal travel and give a
tighter feel to the Brake pedal.

2lb Valves should do it as the M/C is way
above the Calipers.

https://www.compbrake.com/residual-valve-each.html

Regards,

The Gorilla.

[leaded]

Thanks for the reply.

Like you say on track or once they are hot it is even worse. Why are the APs better, do you think they might have some sort of residual valve built in to the caliper already?

There is a chap in the USA that has started to investigate a Z8 master cylinder - Part # 34-31-675-48-801 which has 27mm primary and 20mm secondary bores. This could work but a bit more plumbing and T pieces is needed to incorporate the DSC fittings. (stock BMW E46 M3 brake master cylinder is a tandem unit with a 25mm primary(front) bore and a 20mm secondary(rear) bore)

I have asked my BMW parts guy if it is possible to look at the specs of some other master cylinder to see if there is anything more suitable. E90 M3, E90 M3 GTS, X5, E60 M5/M6 or even newer cars.

Might give those residual valves a go first. Thanks for the link. :beer:

[The Gorilla]

Hi,

Quote - ''Why are the APs better, do you think they might have some sort of residual valve built in to the caliper already?

It was more likely due to the fact that
the AP Calipers piston size/fluid transfer was almost
on the money where as the Alcon ones
are a little oversized.

These kits are produced by and large from 'stock' calipers
so its a case of making what exists fit the
requirement.

Both the AP and the Alcon calipers are not
just specific to BMW 46's.

As a matter of interest have you actually
measured how much the Pads in your
Alcon Calipers back off ?

The problem with altering the M/C
size is that it will alter the pedal ratio.
Which brings another set of issues.

Regards,

The Gorilla.

[shane@mbtech]

Notice my comments on the first page.

After noting this I started to left foot tap the brake ever so slightly just before braking properly. I know lots of race drivers do this, and for me the pedal felt superb.

It's the pads backing off which is causing the issue, so the little tap gets them sitting back close to the disc. Then when back on the brake pedal it was great.