Brake pedal feel after bleeding

[MrPT]

Has anyone tried changing the brake master cylinder to better suit the Caliper sizes, I know that brake force would reduce with a larger MC but it would give better pedal feel?

It would have a similar effect to what maupineda describes when dropping total piston area - less clamping force and the feeling of it being a bit more linear/longer (without the other benefits of upgraded calipers - better heat dissipation, more consistent pad vs disc geometry etc).

I think we're talking about a couple of different things here though - perhaps you can clarify, OP?

"Firmness" is the feeling of a direct connection between your foot and a hard pad making contact with a hard, unyielding disc. "Bite" is the point at which you feel actual retardation kicking in. A lot of non-sports cars have very early and aggressive bite but with crap, spongy pedal feel. If you drive something like the 997 mentioned above, you'll find that Porsche usually like to set up their brakes relatively "long" and progressive by most standards, but the feel is really nice and in some cases it can feel almost as if you're pressing directly on the brake discs with your foot.

With the Z4M, most people think it's unnecessarily over-servo'd, i.e. the brakes bite a bit too early and non-linearly (especially when you consider the fact that they are actually very good at stopping the car and most Z4M drivers can drive a bit). It's the same theme of erring on the side of caution that you find in loads of other areas of the way the car is set up - the rear toe-in and camber, the emergency braking function, intrusive TC, the "I AM BRAKING VERY HARD NOW" brake light display etc.

FWIW, mine bite very early and the feel is ok but not the best. It was improved a bit by upgrading the front calipers, but not night and day. I'm still on stock pads and have rear factory lines, so those are a couple of obvious things to try and upgrade in the future.

[MrPT]

It's worth giving the calipers a few clonks with a rubber mallet when bleeding, BTW. I'm not sure how much of a difference this will make with the stock calipers, but I find loads of little bubbles stuck in the brembos that the INPA ABS routine can't do anything about (and maybe is the source of a lot of them!).

[InterlagosMC]

Has anyone tried changing the brake master cylinder to better suit the Caliper sizes, I know that brake force would reduce with a larger MC but it would give better pedal feel?

It would have a similar effect to what maupineda describes when dropping total piston area - less clamping force and the feeling of it being a bit more linear/longer (without the other benefits of upgraded calipers - better heat dissipation, more consistent pad vs disc geometry etc).

I think we're talking about a couple of different things here though - perhaps you can clarify, OP?

"Firmness" is the feeling of a direct connection between your foot and a hard pad making contact with a hard, unyielding disc. "Bite" is the point at which you feel actual retardation kicking in. A lot of non-sports cars have very early and aggressive bite but with crap, spongy pedal feel. If you drive something like the 997 mentioned above, you'll find that Porsche usually like to set up their brakes relatively "long" and progressive by most standards, but the feel is really nice and in some cases it can feel almost as if you're pressing directly on the brake discs with your foot.

With the Z4M, most people think it's unnecessarily over-servo'd, i.e. the brakes bite a bit too early and non-linearly (especially when you consider the fact that they are actually very good at stopping the car and most Z4M drivers can drive a bit). It's the same theme of erring on the side of caution that you find in loads of other areas of the way the car is set up - the rear toe-in and camber, the emergency braking function, intrusive TC, the "I AM BRAKING VERY HARD NOW" brake light display etc.

FWIW, mine bite very early and the feel is ok but not the best. It was improved a bit by upgrading the front calipers, but not night and day. I'm still on stock pads and have rear factory lines, so those are a couple of obvious things to try and upgrade in the future.

Thanks for the input, so I have rebuilt the callipers all around, fitted brass bushes and am running braided lines with ebc bluestuff pads currently, did have pfc z rated but they weren’t the best for pedal feel. When bleeding I did as prescribed by bleeding the Calipers all around and tapped calipers as they were bleeding. Pedal has more dead travel than I would like but when it bites it feels really good. I just want it that when I press the pedal down I don’t want so much travel before any braking feel

[insider]

Has anyone tried changing the brake master cylinder to better suit the Caliper sizes, I know that brake force would reduce with a larger MC but it would give better pedal feel?

It would have a similar effect to what maupineda describes when dropping total piston area - less clamping force and the feeling of it being a bit more linear/longer (without the other benefits of upgraded calipers - better heat dissipation, more consistent pad vs disc geometry etc).

I think we're talking about a couple of different things here though - perhaps you can clarify, OP?

"Firmness" is the feeling of a direct connection between your foot and a hard pad making contact with a hard, unyielding disc. "Bite" is the point at which you feel actual retardation kicking in. A lot of non-sports cars have very early and aggressive bite but with crap, spongy pedal feel. If you drive something like the 997 mentioned above, you'll find that Porsche usually like to set up their brakes relatively "long" and progressive by most standards, but the feel is really nice and in some cases it can feel almost as if you're pressing directly on the brake discs with your foot.

With the Z4M, most people think it's unnecessarily over-servo'd, i.e. the brakes bite a bit too early and non-linearly (especially when you consider the fact that they are actually very good at stopping the car and most Z4M drivers can drive a bit). It's the same theme of erring on the side of caution that you find in loads of other areas of the way the car is set up - the rear toe-in and camber, the emergency braking function, intrusive TC, the "I AM BRAKING VERY HARD NOW" brake light display etc.

FWIW, mine bite very early and the feel is ok but not the best. It was improved a bit by upgrading the front calipers, but not night and day. I'm still on stock pads and have rear factory lines, so those are a couple of obvious things to try and upgrade in the future.

Very much agree with everything you have written.

I never had a problem with initial bite, if anything it was too pronounced. Since then I've disabled few brake boost flags in ecu/module, maybe that helped a little, but hard to say.

Firmness aka softish pedal - still present. Non-linear and inconsistent braking force according to pedal pressure (e.g. braking at 100kph vs 150kph) - still there. And this is how I would describe brakes that don't inspire confidence, even if they brake well until overheated.

[Beedub]

ap BBK all round here - awesome pedal. Still one of the braking systems ive had the pleasure to use, track use needs a suitable pad however but the change is so quick and easy its not an issue. over 5k now days sadly.

[snotrag]

Good read this - getting a few miles on my recently purchased Z4M and the one thing I'm not happy with is the pedal travel.

Owned lots of cars - never had anyhting like the pedal in this car. Very, very long travel before the bite. Power is there, pulls up fine, no fluid leaks, brakes have been flushed and re-bled - but the pedal is awful as it has such a long, long arc of movement. This also makes heel/toe and moving from throttle to brake awkward. Not enjoying it!

Its as if the leverage ratio of the pedal is wrong.


(Possibly not helped by coming from a Lotus Elise but seriously, my diesel estate car has a better feeling pedal than the Z4m currently).


It appears to be the same issue as this guy had incidentally (and multiple other threads on US forums) but no defined answers.

viewtopic.php?t=42159

[Beedub]

BTW just to note my stock brake setup on the z4m always felt fantastic..... something is amiss with some of these cars.