///m brakes inconsistent?

ajw45 · 07-08-2012, 10:32 PM

I finally got the z4m out to the track this weekend and it was fantastic! The suspension (ast) and alignment were great right off the bat and the oil temp stayed just a few degrees right of center despite the warm weather. The one thing that drove me crazy was the feel of the brakes. Once fully on the brakes they felt fine but part/light brake application was really inconsistent. Sometimes a light breathe on the brakes did nothing, sometimes it really grabbed, both feeling equally light on the pedal, to my foot anyway. They just didn't feel progressive or predictable. Anyone else get this? Would a bbk help with the feel?

Fwiw, I didn't have any heat problems running srf and pfc06 pads and the brakes performed great. My last track car was an e28 m5 with upsized rears and an upsized master cylinder which felt awesome - really stiff pedal, almost as heavy as the clutch, and progressive resistance through the whole pedal travel.

Gratuitous 1M footage!

Caddyshk · 07-09-2012, 07:49 AM

Thanks for sharing! Are you running OE pads?

Kgolf31 · 07-09-2012, 08:13 AM

Quote:

Originally Posted by Caddyshk

Thanks for sharing! Are you running OE pads?

Quote:

Fwiw, I didn't have any heat problems running srf and pfc06 pads

OP - Are you talking about the pads instantly grabbing on the rotor with the pedal, then sometimes not grabbing until more pressure?

Hrm.

Were these problems re-occuring in the same corner, or were they happening at different speeds?

ajw45 · 07-09-2012, 09:33 AM

Quote:

Originally Posted by Kgolf31

OP - Are you talking about the pads instantly grabbing on the rotor with the pedal, then sometimes not grabbing until more pressure?

Hrm.

Were these problems re-occuring in the same corner, or were they happening at different speeds?

Exactly! Same corner, similar speeds, and it seemed hard to judge when the brakes would actually start to grab during that initial pedal travel which is pretty light. I noticed this just driving around on the street with OEM pads when I first purchased the car and have learned to just be extra slow on the brakes. Could this be the active brake assist I'm feeling/fighting?

Scrapped the OEM pads and running PFC 06/08 f/r

Caddyshk · 07-09-2012, 04:07 PM

Quote:

Originally Posted by Kgolf31

OP - Are you talking about the pads instantly grabbing on the rotor with the pedal, then sometimes not grabbing until more pressure?

Hrm.

Were these problems re-occuring in the same corner, or were they happening at different speeds?

Thought he was referencing his last car...

seank · 07-09-2012, 04:39 PM

Brake pedals just move fluid. Master cylinders decide how much fluid is moved. Brake pads determine at what temperatures they grab at and when they don't. BMW electronics could do who knows what in a modern car.

But with my experience, you are having issues with the temperature of your pads. If I remember correctly, that pad (pfc 06) that you are running needs A LOT of heat, so they may be cooling down.

Just a thought, but I am pretty sure it is not the brakes but rather your pads.

txz4 · 07-09-2012, 04:45 PM

I actually notice the same problem. Does it by any chance happen as decelerating and downshifting? thats when its most noticeable to me.

Finnegan · 07-09-2012, 05:09 PM

Take a look at this thread. Sounds very similar to what you're describing, specifically see the posts by The Hack. Thread.

It could also be the active brake assist jumping in there as well. It tries to "help" when really jumping off throttle and onto the brakes. In my experience this seems to happen more when going from WOT to "light touch" braking transition.

Not much can be done about the active brake assist, but if you noticing a less than stellar and firm pedal feel, "The Hack" method of removing air from the braking system is worth a shot. Can't hurt, and might help.

Sean's input should be strongly considered as well, especially if it makes sense given it was the same corner consistently.

StickMon · 07-10-2012, 12:06 AM

Get that all the time on downshifts. I call it "hyper brakes". My guess is it's the compliment of "dead pedal" throttle.
I think both are caused by the computers trying to make sure you don't jump on the brakes and the throttle at the same time and drive through a store front, but the system is too slow if you have fast feet.
If I downshift without braking, throttle blips are predictable and effective. If I get on the brakes first, then try and blip for a downshift, throttle response is negligible, because it thinks I'm still braking and kills the throttle response. Have to smack it to the floor twice, then miss the apex because I've spent too much time fighting with the car.
Once I do get it blipped and downshifted and get back on the brake, the slightest touch on the brake pedal nearly locks them up. Lift a little and reapply: back to normal brake response.

It's too binary to be a hydraulic issue. I don't have a long spongy pedal. Brakes are firm, smooth, and predictable, except when getting on them fast after hard throttle. But even that's becoming predictable. The car's programming me. (2 blips for a downshift then eeaassyy on the brake, cause it's gonna grab like a pissed off cat. Lift a little and reapply. Damn, missed the apex again.)

The HACK · 07-10-2012, 10:47 AM

If I have to guess, I'm going to say this particular corner is at the end of a long straight? And the long straight is followed by a couple of potentially moderate to high speed corners that does not require braking?

I suspect it's a combination of brake technique and compound.

StickMon · 07-11-2012, 10:55 PM

In my particular case, it's at the bottom of a long off ramp at the end of a long freeway.

07-08-2012, 10:32 PM	#1
ajw45 Private First Class 32 Rep 149 Posts Drives: Z4M Coupe Join Date: Feb 2011 Location: Boston iTrader: (0)	///m brakes inconsistent? I finally got the z4m out to the track this weekend and it was fantastic! The suspension (ast) and alignment were great right off the bat and the oil temp stayed just a few degrees right of center despite the warm weather. The one thing that drove me crazy was the feel of the brakes. Once fully on the brakes they felt fine but part/light brake application was really inconsistent. Sometimes a light breathe on the brakes did nothing, sometimes it really grabbed, both feeling equally light on the pedal, to my foot anyway. They just didn't feel progressive or predictable. Anyone else get this? Would a bbk help with the feel? Fwiw, I didn't have any heat problems running srf and pfc06 pads and the brakes performed great. My last track car was an e28 m5 with upsized rears and an upsized master cylinder which felt awesome - really stiff pedal, almost as heavy as the clutch, and progressive resistance through the whole pedal travel. Gratuitous 1M footage! Last edited by ajw45; 07-08-2012 at 10:39 PM..
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07-09-2012, 07:49 AM	#2
Caddyshk M = Midlife Crisis 65 Rep 2,006 Posts Drives: 2006 Z4MC Interlagos Join Date: May 2007 Location: Fort Erie, Ontario, Canada iTrader: (0)	Thanks for sharing! Are you running OE pads? __________________ 2006 Z4MC - #LL93158 SS Race Cans, RE X Pipe, DKF Sec 1, Fabspeed Headers, OE STB, AS Shifter, Dave Z CDV, GC Coil Overs, Stoptech lines, Hawk DTC Pads, RE Clutch Stop, RE Transmission Mounts, Vibra-Technics Engine Mounts, Poly FCAB & RTAB, LeatherZ M Shift Boot, Tekarbon Rear Spoiler, CF Grills, Advan RS DGM
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07-09-2012, 04:39 PM	#6
seank enthusiast 48 Rep 1,695 Posts Drives: e30 m3,e90 wagon,sprinter,z4m Join Date: Dec 2011 Location: sacramento, ca iTrader: (4)	Brake pedals just move fluid. Master cylinders decide how much fluid is moved. Brake pads determine at what temperatures they grab at and when they don't. BMW electronics could do who knows what in a modern car. But with my experience, you are having issues with the temperature of your pads. If I remember correctly, that pad (pfc 06) that you are running needs A LOT of heat, so they may be cooling down. Just a thought, but I am pretty sure it is not the brakes but rather your pads.
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07-09-2012, 04:45 PM	#7
txz4 Major 59 Rep 1,097 Posts Drives: 2006 M coupe Join Date: Oct 2010 Location: san antonio, texas iTrader: (3)	I actually notice the same problem. Does it by any chance happen as decelerating and downshifting? thats when its most noticeable to me.
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07-09-2012, 05:09 PM	#8
Finnegan Dog Listener 703 Rep 7,850 Posts Drives: Z4M/. Z3M, E36/46 M3 Join Date: Oct 2008 Location: Teaching the dog to slalom iTrader: (22)	Take a look at this thread. Sounds very similar to what you're describing, specifically see the posts by The Hack. Thread. It could also be the active brake assist jumping in there as well. It tries to "help" when really jumping off throttle and onto the brakes. In my experience this seems to happen more when going from WOT to "light touch" braking transition. Not much can be done about the active brake assist, but if you noticing a less than stellar and firm pedal feel, "The Hack" method of removing air from the braking system is worth a shot. Can't hurt, and might help. Sean's input should be strongly considered as well, especially if it makes sense given it was the same corner consistently. Last edited by Finnegan; 07-09-2012 at 05:21 PM..
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07-10-2012, 12:06 AM	#9
StickMon My other car is on Mars 636 Rep 3,124 Posts Drives: 2006 MR Join Date: Feb 2011 Location: Lo-Cal iTrader: (1)	Get that all the time on downshifts. I call it "hyper brakes". My guess is it's the compliment of "dead pedal" throttle. I think both are caused by the computers trying to make sure you don't jump on the brakes and the throttle at the same time and drive through a store front, but the system is too slow if you have fast feet. If I downshift without braking, throttle blips are predictable and effective. If I get on the brakes first, then try and blip for a downshift, throttle response is negligible, because it thinks I'm still braking and kills the throttle response. Have to smack it to the floor twice, then miss the apex because I've spent too much time fighting with the car. Once I do get it blipped and downshifted and get back on the brake, the slightest touch on the brake pedal nearly locks them up. Lift a little and reapply: back to normal brake response. It's too binary to be a hydraulic issue. I don't have a long spongy pedal. Brakes are firm, smooth, and predictable, except when getting on them fast after hard throttle. But even that's becoming predictable. The car's programming me. (2 blips for a downshift then eeaassyy on the brake, cause it's gonna grab like a pissed off cat. Lift a little and reapply. Damn, missed the apex again.) Last edited by StickMon; 07-10-2012 at 12:23 AM..
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07-10-2012, 10:47 AM	#10
The HACK Midlife Crises Racing Silent but Deadly Class 1821 Rep 5,337 Posts Drives: 2006 MZ4C, 2021 Tesla Model 3 Join Date: Oct 2007 Location: Welcome to Jamaica have a nice day iTrader: (1)	If I have to guess, I'm going to say this particular corner is at the end of a long straight? And the long straight is followed by a couple of potentially moderate to high speed corners that does not require braking? I suspect it's a combination of brake technique and compound. __________________ Sitting on a beat-up office chair in front of a 5 year old computer in a basement floor, sipping on stale coffee watching a bunch of meaningless numbers scrolling aimlessly on a dimly lit 19” monitor.
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07-11-2012, 10:55 PM	#11
StickMon My other car is on Mars 636 Rep 3,124 Posts Drives: 2006 MR Join Date: Feb 2011 Location: Lo-Cal iTrader: (1)	In my particular case, it's at the bottom of a long off ramp at the end of a long freeway.
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