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      02-20-2015, 10:58 AM   #1
Varinn
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///M Brake performance

Not sure about anyone else, but the stock brakes on the Z4M seem to be extremely overpowered for street use. In stop and go traffic or when going hard into an occasional corner they are very soft and grabby at the top of the pedal, though they even out a bit once into it. The touchiness makes heel-toe shifting damn near impossible (for me) which is a non-existent problem on my e30 wether it's on the track or street sets. I've had a few other friends drive the car and we all had the same impression, the brakes are too damn sensitive on initial bite and the pedal seems vastly over boosted. It almost feels as if it pulls itself down.

I've already flushed the fluid with ATE Typ200 and bled as well as I could and it still felt soft.

I'm installing StopTech street performance this weekend and I hear they do well to reduce the grabbiness on the stock textars (plus there should be less dust!)

Is it worth taking it to my buddy at the dealership and having him do a power bleed with their system while cycling the ABS?

Are SS lines worth it? I noticed no change when swapping them on the e30, will I notice any on the Z? I'm not interested in going with a BBK, though I would love a stock sized option for a fixed 4pot caliper if anyone knew of one
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Last edited by Varinn; 02-20-2015 at 11:56 AM..
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      02-20-2015, 12:10 PM   #2
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I have StopTech Street pads on my M as well, like them so far. As for the SS brake lines, they aren't expensive but unless you're doing a lot of track days I don't think it's worth the money.
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      02-20-2015, 01:32 PM   #3
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How do they compare in feel to stock pads? I mean, I'll find out myself in a day or two but I may as well ask now. Such a shame that BMW couldn't fit our cars with better calipers from the factory when some of the cheaper Japanese sports cars were coming with wonderful 4pots, stock (and 10 years earlier even!)
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      02-20-2015, 01:59 PM   #4
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Quote:
Originally Posted by Varinn View Post
How do they compare in feel to stock pads? I mean, I'll find out myself in a day or two but I may as well ask now. Such a shame that BMW couldn't fit our cars with better calipers from the factory when some of the cheaper Japanese sports cars were coming with wonderful 4pots, stock (and 10 years earlier even!)
Caliper is but 1 of 3 major part of the braking equation. Rotors and pads have much larger immediate impact on actual braking performance. Rotor provide heat dissipation and leverage for brake torque, while pads provide friction.

BMW actually put one of the most advanced brake rotors they make on our beloved MZ4s. The center mounted, floating 2 piece rotors are not found on any of those "wonderful" 4 pot stock Japanese cars. For track and performance applications, I'd take the brakes on our car over those fixed 4 pot calipers that came OE on a lot of Japanese cars ANYDAY.

Case in point. 350Z track model comes with 4 piston front, 2 piston rear BREMBO brakes. 300+ HP on 3,400 lbs with gobs of torque and a stiff, relatively short chassis. Very comparable to our MZ4 Coupe in terms of what's on paper. Back in 2005/6 time frame, a fellow enthusiast had a 350Z at one of the local, brake intensive tracks, and within 2 sessions he was superheating his brakes that the car was basically un-drivable. When we cracked open his calipers to bleed out the brakes, the brake fluid was FOAMING as it comes out due to how hot the system has gotten.

I had a hell of a time trying to chase down braking issues on my own 350Z (not the track model) and Subaru WRX (not the STi) to know that those fancy Brembo calipers aren't the solution to the problem. They're all equipped with single piece rotors that are TOO SMALL for the size and power those cars can generate.

On the MZ4, you really only need to change pads and fluid for performance applications all the way up to stock class motorsport applications. Anything above that you can and probably should consider caliper upgrades as well, as the calipers ARE the single weak point in what otherwise is a very VERY stout performance system.

On stainless steel braided lines for the MZ4, I personally feel they're not worth the hassle on this car, because the rear line is a compound line composed of two separate lines for each side. To change them out and do it right is a real pain in the @ss. Plus you introduce the possibility of air getting in and trapped in the ABS system if you leave the line open for too long in the process of changing out the brake lines. On top of all that, I believe the lines on the MZ4 is already nylon braided and do not bulge and expand like old school rubber lines, so the benefits of SS lines on the MZ4 is really marginal.

I think you should have a dealership or mechanic hook your car up to a GT1 or equivalent diagnostic system that is capable of cycling the ABS to make sure all the old fluid and air is evacuated from the car. To be completely honest, the MZ4 seem to share the same "issue" with the E36 M3, when the system is cracked open and bled/flushed, you will NEVER get that rock solid feel back on the pedals. I don't know why that is, but it's been my experience since the first bleed back in 2006. But using a GT1 to cycle the ABS pump (or going out and activating ABS a few times and then bleed again) seems to return the stiff pedal back to about 80% of new.
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      02-20-2015, 03:47 PM   #5
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Quote:
Originally Posted by The HACK View Post
Caliper is but 1 of 3 major part of the braking equation. Rotors and pads have much larger immediate impact on actual braking performance. Rotor provide heat dissipation and leverage for brake torque, while pads provide friction.

BMW actually put one of the most advanced brake rotors they make on our beloved MZ4s. The center mounted, floating 2 piece rotors are not found on any of those "wonderful" 4 pot stock Japanese cars. For track and performance applications, I'd take the brakes on our car over those fixed 4 pot calipers that came OE on a lot of Japanese cars ANYDAY.

Case in point. 350Z track model comes with 4 piston front, 2 piston rear BREMBO brakes. 300+ HP on 3,400 lbs with gobs of torque and a stiff, relatively short chassis. Very comparable to our MZ4 Coupe in terms of what's on paper. Back in 2005/6 time frame, a fellow enthusiast had a 350Z at one of the local, brake intensive tracks, and within 2 sessions he was superheating his brakes that the car was basically un-drivable. When we cracked open his calipers to bleed out the brakes, the brake fluid was FOAMING as it comes out due to how hot the system has gotten.

I had a hell of a time trying to chase down braking issues on my own 350Z (not the track model) and Subaru WRX (not the STi) to know that those fancy Brembo calipers aren't the solution to the problem. They're all equipped with single piece rotors that are TOO SMALL for the size and power those cars can generate.

On the MZ4, you really only need to change pads and fluid for performance applications all the way up to stock class motorsport applications. Anything above that you can and probably should consider caliper upgrades as well, as the calipers ARE the single weak point in what otherwise is a very VERY stout performance system.

On stainless steel braided lines for the MZ4, I personally feel they're not worth the hassle on this car, because the rear line is a compound line composed of two separate lines for each side. To change them out and do it right is a real pain in the @ss. Plus you introduce the possibility of air getting in and trapped in the ABS system if you leave the line open for too long in the process of changing out the brake lines. On top of all that, I believe the lines on the MZ4 is already nylon braided and do not bulge and expand like old school rubber lines, so the benefits of SS lines on the MZ4 is really marginal.

I think you should have a dealership or mechanic hook your car up to a GT1 or equivalent diagnostic system that is capable of cycling the ABS to make sure all the old fluid and air is evacuated from the car. To be completely honest, the MZ4 seem to share the same "issue" with the E36 M3, when the system is cracked open and bled/flushed, you will NEVER get that rock solid feel back on the pedals. I don't know why that is, but it's been my experience since the first bleed back in 2006. But using a GT1 to cycle the ABS pump (or going out and activating ABS a few times and then bleed again) seems to return the stiff pedal back to about 80% of new.
Greatly appreciate the thorough response, lots of info there but I think you may have misread my post (or I wasn't very clear)

The massive floating rotors are great, I have no issues with them beyond the cost associated with replacing the set. I have no problem with the brakes not having enough torque to stop the car in any situation I'm finding myself in. My only concern with the braking on the Z4M is that the pedal is too soft with a very powerful initial bite that I personally find hard to modulate. My e30 is my track car, the Z4 is more for weekend mountains and sunny day drives to work where I will never reach the temperatures or demands to need a rotor upgrade. Calipers however... As you say they are the weak point. I'm looking at my problem as being one of (or a combination of) a few things. Improper bleeding (I did it like I would my e30, pump pump pump hoooooold) without GT1 or a power bleeder, large "flexible" floating calipers, and grabby stock pads.

I'll take your advice and hook it up to GT1 to cycle ABS during the bleed process as it's easier than going out for a boot mid way through. I'll also hopefully see a slight improvement with the StopTech pads. If these don't do what I want from them and return the pedal to feeling firm how I think it should I might try to find a set of StopTech, Brembo, or Wilwood calipers for the stock front rotors. I should never have to touch the oem discs. As an exclusively street car I will never reach brake fade levels of heat in the stock set.

I've heard lots of back and forth on the lines with some saying they are stock braided, some say they are not. Regardless, the general consensus seems to be that they do not make a noticeable difference. I would almost bet that any improvement felt comes more from the new fluid with full bleed and the impact to the wallet that goes with replacing the lines.
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      02-21-2015, 10:45 AM   #6
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I haven't really tested the pads that hard to notice much of a difference, but they don't seem to dust a lot. They have a lot of bite even when they are cold.

As for the calipers and pistons, more isn't always better.
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      04-04-2015, 06:33 PM   #7
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The soft pedal is indeed as designed, but don't forget that when you're braking hard at high speed, it firms up significantly. I guess they designed it this way for comfortable braking. But that's subjective.
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      04-04-2015, 07:38 PM   #8
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the StopTech street pads are a nice upgrade. Easy to modulate. Otherwise, stop whining, you'll eventually get used to the stock brakes
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      05-22-2015, 01:37 PM   #9
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I find that the stock pads are inadequate, both for street and track. They get way too hot on a track and can eventually warp the rotors. On the street at lower speeds they are too grabby and hard to modulate.

That being said, the rotors and calipers are more than up to the task, even for hard-lapping on long and short tracks. Try changing the pads. I run PFC 01s for track days and they stop the car like an anchor. For the street the PFC Z are amazing (and give off less dust than OEM). I used to track with the Z pads, but as I got faster, they weren't quite what I needed. The only negative with the Zs on the road is that there is a low-frequency thrum that you can hear as you brake. I can live with it, but it's noticeable. I have just installed EBC Greenstuff pads for the street in the last 50 kms, so we'll see how those are.
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      06-03-2015, 10:22 AM   #10
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Question, if you're not dipping into ABS while braking, would the presence of old fluid in the ABS system affect pedal feel (after a standard vacuum bleed without using a GT1)?
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      11-03-2015, 11:07 AM   #11
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I run stock pads on the street and Carbotech 10 & 8 for the track. As a BMWCCCA track instructor I have yet to feel that the stock calipers were not up to the track (Circuit of the Americas)abuse much less the normal daily driving stress. The brake fluid I run is Castrol SRF. I have boiled Motul RBF 600 & 660 at the track, never the Castrol. MAYBE s set of StopTech calipers would make a difference but at $3K thats a hard sell for me.
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      11-03-2015, 11:14 AM   #12
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Quote:
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The brake fluid I run is Castrol SRF. I have boiled Motul RBF 600 & 660 at the track, never the Castrol.
Interesting. The most plausible explanation for my earlier track experiences.
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