Pad Knockback - wheel bearing upgrade

Vanne · 06-14-2021, 02:24 AM

hey Andre,

have you seen/checked this??? its from an e86 coupe, non M.

"I had the opposite problem where the DSC was constantly on! My preference is for ABS on and DSC off which I achieved by disconnecting the steering angle sensor. However, prolonged disconnection seems to cause a soft brake pedal so it's occasionally reconnected."

i wonder if its the steering angle sesnor...?????? is yours disconnected? I am not sure how it causes soft pedal, but there you have it, maybe check it out.

dre99gsx · 06-14-2021, 08:33 PM

Hey Vanne, thanks for the observation.

Since the 2jz swap and the oem ECU not getting valid engine signals (other than tach), the DSC is always off. ABS is ON and functioning. I know this since last year my ABS/DSC module had the trifecta-lights and I ran a few track events with no ABS. I replaced the ABS/DSC with a rebuilt unit. Steering angle sensor is working though and no errors from angle sensor that I know of. I have electric power steering so I know it works...

Having said all of that, I've never had DSC working on this car for 3+ years. How in the world would no DSC cause soft pedal? (or does that guy say disconnected steering angle is what caused soft pedal?)

I have master cyl block off plugs and another 'new' master cylinder coming in a few days, will test / isolate and chase this down. Chances are the ABS module is bypassing fluid very slowly although I don't know it would do that.

Quote:

Originally Posted by Vanne

hey Andre,

have you seen/checked this??? its from an e86 coupe, non M.

"I had the opposite problem where the DSC was constantly on! My preference is for ABS on and DSC off which I achieved by disconnecting the steering angle sensor. However, prolonged disconnection seems to cause a soft brake pedal so it's occasionally reconnected."

i wonder if its the steering angle sesnor...?????? is yours disconnected? I am not sure how it causes soft pedal, but there you have it, maybe check it out.

Vanne · 06-15-2021, 02:53 AM

yeah, hes saying the diconnected steering angle causes soft pedal.. how? beats the shit out of me, but it does.. hes fixed it with a switch that he can momentarily turn on, once a day before track and then off again, and it all functions as it should, leave it disconnected for a period of time and whola..,. soft brake pedal.... hes got electric steering aswell..

no idea how, but thats what it is...

dre99gsx · 06-15-2021, 09:20 PM

The internets is full of crazy theories..

https://rennlist.com/forums/993-foru...-abs-pump.html

These guys have issues with ABS building some sludge that causes abs valves to stick, which is one way fluid could circulate/bypass internally and cause a sinking brake pedal.

I may try flushing my entire system with denatured alcohol and use cheap dot3 to do testing. Running through SRF is getting hella expensive

I did block off my calipers and sinking still occurs. Waiting on master cylinder but may have to buy another ABS/DSC module if I'm going to start throwing parts at it.

Half of the people I've talked to say this is normal, the other half say it is not. What a crazy place to be in...

dre99gsx · 06-16-2021, 07:31 PM

UPDATE:

Interesting. I blocked off the master cylinder with plugs. ROCK SOLID pedal even with 26in/hg vacuum applied to booster. So, MC checks out Ok.

I hooked it back up to the ABS/DSC, then plugged all 4 output ports of the ABS. ROCK SOLID pedal, no drop.

This leaves the lines -> calipers. Since I didn't see any leak in the calipers externally, this can only mean something between the ABS and caliper(s) is leaking and I cannot see it, or, the fluid is bypassing the caliper piston seals. Or, there is some stubborn air bubble in the caliper. Remember, stoptech trophies up front, 135i fixed calipers in the rear.

Now I will connect one by one and see what I find.

Hooked up the rear brakes, first left rear, then both. Pedal had a slight more slow drop but I would say about .5" in 10 seconds, it was almost nothing. I don't see the rear brake calipers/lines contributing.

This now leaves the front lines/calipers.

I connected driver caliper to ABS unit, everything else blocked off. Low and behold, the pedal starts slowly sinking. I then disconnected the caliper from the stoptech SS flex brake line and create a cap at the end of the banjo-bolt. I suspected the brake line was expanding. Nope. ROCK HARD pedal.

So now this leaves me with the stoptech trophy caliper. It's funny, I've had nothing but unsatisfying brake feel ever since I swapped these bad boys in. I'm not sure what it could be, there is no fluid loss that can be found. Perhaps the two halves of the caliper are expanding from each other, but that would be a horrible design. I did put a solid block of metal between the caliper pistons to completely isolate the caliper, and watched it was someone else pressed the brake. I couldn't see anything from outside.

It seems like the fluid could be weeping past the pistons seals. Going to call up stoptech or do more research.

dre99gsx · 06-17-2021, 08:02 PM

Ok. I've reached a potential stopping point.

Called stoptech, they just shrugged their shoulders and said "we don't know". So, I'm on my own here.

I took the caliper apart, cleaned and rebuilt it. Actually tested it on the bench, each half separately. Both vacuum and 100psi + soapy water on the whole damn thing. I was going to even submerge it under water too.

Both halves have no leak issues. I clamped the pistons on with a metal plate to keep them from moving.

I went back to the car just to triple check - I have the brake line capped with an aluminum plug. Pedal is Rock solid.

I hook up the caliper, bleed with a powerbleed, tappign with hammer, back and forth (inner and outer bleed screws). There is no air left I'm certain. Get back in the car, pump brakes, hold, and they start sinking.

As they are sinking, I hear a "clink"... "clank" sound coming from the caliper, almost as if the immense pressure is straining the parts. But, I don't think it's related.

Matter of fact, I even clamped both halves with a C-clamp on the outside just in-case the halves were pushing apart! No change.

I'm starting to suspect this is some kind of design issue or like I mentioned in the previous post, the fluid is weeping past the piston seals just a tad bit, but not enough to leak out. Or, there is air trapped between the piston seals and the piston walls that never evacuates. I have no idea.

I'm out of options. I may have to source another set of calipers and spend $, I think it's $800/ea for new ST40s with Z4M piston sizes. And if I chance it, buy them, and same issue, then I'm going to be upset and poor.

inTgr8r · 06-17-2021, 08:12 PM

wow..... just caught up on this thread again.
Amazed that this is still unsolved!

Sorry to hear that all the time & resources that you've poured into this haven't yielded a solution.

Vanne · 06-18-2021, 07:44 AM

Bloody hell mate, what a run around... At least youve come a hell of a long way isolating out parts that it /could/ have been. If pressure was dropping as fluid was going past the seals, then surely that would show..somewhere in a mess?

GuidoK · 06-18-2021, 08:41 AM

Quote:

Originally Posted by dre99gsx

Matter of fact, I even clamped both halves with a C-clamp on the outside just in-case the halves were pushing apart! No change.

I assume when you capped of the brake lines you did it at the end of the flexible hoses?

Have you measured with a micrometer how much the calipers are flexing when firmly pressing the pedal? (without the C clamp on)

I suppose you've checked but do your pistons have dust seals? And maybe fluid gets between the dust seals and the piston seals?)

But reading this I can't imagine you have a leak. You've been at it for so long, you'd seen fluid.
Especially if you feel the pedal sinking.

But imo that only leaves 2 options:
1. there is still air
2. the pistons keep expanding, so there is deformation somewhere.

I mean the fluid has to go somewhere

I can imagine that this problem drives you crazy

dre99gsx · 06-18-2021, 02:56 PM

Correct, capped at the end of the flexible hose (banjo bolt), so I can verify the hoses themselves weren't flexing.

I'm going to test that next - dial caliper on the brake caliper and measure flex/growth. Good call. No dust seals on the pistons, I can see directly if any fluid is weeping and possible going back into it's hiding spot. Clean as a whistle.

I even left hoses on the nipples with some fluid to see if the fluid level moves up or down (or bubbles) when pressing brake pedal. Seems the bleeder screws are tight.

I'm suspecting deformation now. I hear a "click" "clack" when doing this test, almost as if the aluminum caliper is deforming.

I have another theory, and this one is starting to seem more plausible. For what it's worth, all of this work may help someone else who runs into this issue, so glad we're working on all possibilities.

I looked up some things, Z4 and Z4M have different part numbers for vacuum booster and master cyl, but same ABS/DSC parts. So, if we assume the boosters are the same functionally (same assist per unit of vacuum), that leaves the master cyl. I’m still on the Z43.0si MC and booster. STR-40 kit w/355 rotors, 38/44 piston is what I currently have. Custom brackets to adapt them to Z4 3.0si knuckles.

Z4M MC (same as E46 M3) master ports are 25.54mm fr / 20.65mm r, Z4M OEM front caliper piston 60mm, 345mm OEM rotor
Z4 MC (same as E46 330i) master ports are 23.81mm fr / 22.2mm r, Z4 OEM front caliper piston 57mm, 325mm OEM rotor

So Z4M has larger MC and larger OEM piston up front, larger rotor. Z4 has smaller for both.

If Stoptech felt the Z4 3.0si 332mm kit with 30/36mm pistons was an appropriate swap to maintain displacement and bias, but instead I’m on 38/44 (and larger rotor) from the Z4M kit, I have 655 displacement increase which is quite large. I may be overpowering the Trophy caliper. Technically, if the 38/44 was meant for the Z4M, which has an even larger master cyl., I would guess that it would be even worse in that setup.

Or, the much larger pistons mean a small amount of movement on the piston side (but normal for what the caliper would move to compress pads onto rotor) equals a much larger movement on the brake pedal size, exaggerating what I am experiencing? If so, It would make sense to move to a larger MC or smaller Trophy caliper piston group.

If I upgrade to Z4M MC, it does change my fr/rear bias (more front, less rear) and I purposely wanted more rear for my driving style. So, I would have to do the math to see what I would lose.

Will get back to you with more tests. A buddy of mine is letting me try his trophy caliper as another data point.

dre99gsx · 06-18-2021, 10:35 PM

Just tested a 6-piston Trohpy caliper from an Audi RS4. This has 36,34 and 30 mm piston sizes. Do the math, total of 2630mm2 surface area. My Z4M calipers of 38 and 44 = 2650mm2. Roughly the same.

This caliper exhibited the same pedal dropping, which now makes it obvious that 3 calipers can't be air in system or a faulty caliper (or even design). I've driven this Audi at the track with this trohpy kit and the brakes are amazing. His car does not have this pedal drop issue either.

Next up is an E46 M3 master cylinder. Should have a result from that soon on whether going larger front bore size reduces the pressure exhibited on the caliper at the amount of pressure my leg can supply.

I do have to make a correction, the M3 MC has larger front bore size, which should reduce front pressure, but smaller rear bore size than my Z4 MC, which should increase rear pressure. This should move my brake bias further back, and that would be Ok. I can drop my rear pad co.friction and compensate if needed. I just hope that I don't then introduce this issue now to my rear calipers

wdb · 06-19-2021, 03:22 PM

Phenomenal detective work.

GuidoK · 06-19-2021, 09:23 PM

Quote:

Originally Posted by dre99gsx

I do have to make a correction, the M3 MC has larger front bore size, which should reduce front pressure, but smaller rear bore size than my Z4 MC, which should increase rear pressure. This should move my brake bias further back, and that would be Ok.

Doesn't the brake bias move foreward?
I thought the ratio of the size of the pistons determined that? (volume driven system)
(with the z4 master cylinder, the ratio is closer to 1:1)

It makes sense to have more bias to the front for the z4m master cylinder because it's also fitted to the m3 which has about equal size front&rear discs. Too much rear bias is dangerous for a daily driver of course.

But the 335i calipers (the ones where you didn't had the problems) do have slightly smaller piston area: 2437mm²

dre99gsx · 06-20-2021, 11:10 AM

You're right in that the Z4 is closer 1:1, but the rotor sizes and Z4 caliper piston sizes are different as well to the Z4M, thus there are a few more variables there..

If I'm pushing down 100lb with my leg on the brake, my end goal is to reduce the distance the caliper piston moves per inch of leg travel. I want to make the front brakes weaker. Another way to put it, I want to NOT be able to flex the front caliper with 100lb of leg force.

So, I can either go to smaller caliper piston sizes, or larger MC bore size. I may already have too much front bias with my current system.

A larger MC bore size will move the same amount of fluid but at (less distance) at the same leg pressure

Pascal
100lb leg force on pedal
1" pedal travel

Z4 MC
Pressure=F/Area
100/445(z4 MC area) = .224 PS

Stoptech caliper piston
Force = Pressure * Area
.224 * 2653(stoptech pistons area) = 596lb.
So, 100lb leg force creates 596lb caliper force

Now the bigger bore Z4M MC
Z4M MC
Pressure=F/Area
100/512(z4M MC area) = .195 PS

Stoptech caliper piston
Force = Pressure * Area
.195 * 2653(stoptech pistons area) = 518lb.
So, 100lb leg force creates 518lb caliper force

Less force created at the same leg pressure. You can also calculate the distance move at the caliper.
Z4 -> 445*1" / 2653 = .167"
Z4M -> 512*1" / 2653 = .192"

What this means is at 100lb leg pressure, the front pistons will have less force at the same distance traveled. But, the rear pistons will have greater force because the MC rear bore size goes in reverse, so I am moving the bias back probably by quite a bit.

The 335I front calipers had a 57mm diameter, and the Z4 has a 57mm diameter piston. They were exact matches in the regards, but of course I was using different rotor sizes anyway. I was on the 345mm Z4M rotor with the 335i caliper. I'm on a 355mm rotor with the Stoptech caliper. So:

345mm rotor, 2437mm2 vs 355mm rotor, 2653mm2. Probably more significant front bias between the two there...

Will find out soon enough when I receive the Z4M MC if the math checks out! lol

If this all works out, I'll need to be careful on the track with too much rear bias. I can downgrade the rear pads a bit since I'm on PFC08. I can go to the stoptech sports perhaps with less Co.Friction.

135i rear piston is 42mm and I have Z4M rear rotor (328mm) , Z4 stock piston is 40mm (294 rotor), so I've already increased the rear braking advantage by quite a bit.

Attached a worksheet, I think I have all the OEM numbers correct. If the math is accurate, I'll be moving from 70/30 to 67/33 bias. Feel free to verify!

Vanne · 06-21-2021, 05:41 AM

Hmm.. lemme get my pop-corn....

Andre, your saying that your over-servo-ing the front brakes and thats why your getting pedal drop because your deforming the front calipers? doesnt really sound plausible mate, but easily tested, remove the vacuum line from the brake booster...

see what happens...

i also highly doubt that if you /ARE/ deforming the caliper, that its elasticity is such that it returns to its original state before deformation.. (especially if you consider how many times youve done this per lap)

anyhows, ill wait to see how you get on with your latest findings. fingers crossed.

GuidoK · 06-21-2021, 09:24 AM

Quote:

Originally Posted by dre99gsx

What this means is at 100lb leg pressure, the front pistons will have less force at the same distance traveled. But, the rear pistons will have greater force because the MC rear bore size goes in reverse, so I am moving the bias back probably by quite a bit.

I always thought that in the MC internally the front and rear cylinder are coupled.
So the front and rear cylinder will always move the same distance when you apply the brakes.
And the larger the cylinder, the more fluid will be moved, resulting in greater pressure.
The larger cylinder is always in front and pushes the smaller cylinder. So the smaller cylinder cant travel a longer distance.

But your explanation also makes sense, so I really don't know what will happen.
It would be interesting to measure the pressure in the lines with the z4 MC and z4m MC, both with calipers attached.

Frank851 · 06-21-2021, 12:11 PM

Quote:

Originally Posted by dre99gsx

Just tested a 6-piston Trohpy caliper from an Audi RS4. This has 36,34 and 30 mm piston sizes. Do the math, total of 2630mm2 surface area. My Z4M calipers of 38 and 44 = 2650mm2. Roughly the same.

This caliper exhibited the same pedal dropping, which now makes it obvious that 3 calipers can't be air in system or a faulty caliper (or even design). I've driven this Audi at the track with this trohpy kit and the brakes are amazing. His car does not have this pedal drop issue either.

Next up is an E46 M3 master cylinder. Should have a result from that soon on whether going larger front bore size reduces the pressure exhibited on the caliper at the amount of pressure my leg can supply.

I do have to make a correction, the M3 MC has larger front bore size, which should reduce front pressure, but smaller rear bore size than my Z4 MC, which should increase rear pressure. This should move my brake bias further back, and that would be Ok. I can drop my rear pad co.friction and compensate if needed. I just hope that I don't then introduce this issue now to my rear calipers

I have the Stoptech trophy calipers front and rear on my Z4MC with SS Stoptech flex lines on each caliper. The rest of my braking system is bone stock OEM. I am running a non-stock brake fluid, don't have the brand as I'm due now for a flush/change. I've never had any issues with my brakes.

I would try properly bleeding the ABS as that seems like the one component in the system that you did not address, but I didn't read the entire thread.

Hope you find the cause so you can enjoy the brakes that you have installed.

dre99gsx · 06-23-2021, 05:45 PM

BOOM... problem solved.

MK60 E46M3 2003-2007 MC with 25.54 front port / 22.2mm rear port (vs my Z4 23.81mm front port / 22.2mm rear port) swapped in, and pedal does not sink to floor.

It all makes sense. I had too much pressure going to front calipers at 70%front/30% rear ratio after all the calculations. I am now 67% front/33% rear (theoretically).

I learned a valuable lesson. Sorry for dragging you all along on this. Port matching / piston matching is very important if you are doing any brake upgrades.

This doesn't solve the pad-knockback issue, although I won't know until I hit the track, but hopefully this gives me the consistent pedal I've been missing for years.

Will report back on how it feels at the track. The other unknown is this Dorman MC M630897 I purchased (not the BMW OEM unit). I did call up dorman and they confirmed the port sizings, but who knows if this thing will survive track duty. I know this is being cheap but whatever...

Thanks for all the help on here.

GuidoK · 06-23-2021, 05:57 PM

Did you also replace the brake servo unit?
That is also bespoke Z4m

Quote:

Originally Posted by dre99gsx

The other unknown is this Dorman MC M630897 I purchased (not the BMW OEM unit).

Do you think Dorman made it's own casting?
Lots of times (with the european aftermarket) the parts are OEM but the BMW (and maybe ATE) markings are either filed away or in the mold an insert is placed blanking out BMW or OEM logos.
OEM is ATE afaik.

I wonder if it's beneficial for me to place a Z4m MC.
I have the 135i brembo set.
On the 135i the MC is the same for normal (54mm, so same as z4) and Brembo calipers.

Quote:

MK60 E46M3 2003-2007 MC with 25.54 front port / 22.2mm rear port

Quote:

Z4M MC (same as E46 M3) master ports are 25.54mm fr / 20.65mm r

So is the z4m MC rear 22.2mm or 20.65mm?

dre99gsx · 06-23-2021, 06:41 PM

Quote:

Originally Posted by GuidoK

Did you also replace the brake servo unit?
That is also bespoke Z4m

I did not. I do know the part numbers are different, and the shells look different as well, but I couldn't find any information on whether the diaphram is different size (which could also impact the amount of assist I get). I inspected mine and tested it obviously, and it's in good shape to my knowledge...

Quote:

Originally Posted by GuidoK

Do you think Dorman made it's own casting?
Lots of times (with the european aftermarket) the parts are OEM but the BMW (and maybe ATE) markings are either filed away or in the mold an insert is placed blanking out BMW or OEM logos.
OEM is ATE afaik.

They definitely did. The casting is different in many areas. The base mount is slightly thicker as well. But, no issues installing it. The Dorman rep mentioned they have engineering drawings (which they can't release) so I'm sure it's all in house design. There are two lower ports that are capped with set screws for the brake sensors, which I don't use. Nice to know that I can connect something to my AEM for brake pressure monitoring.

From what I've researched, the Z4M uses the E46 MK60 MC (2003+) which is 25.54/22.2. The E46 2001-2003 MK20? has 25.54/20.65 and isn't used on Z4M. But, I could go MK20 and have even more front bias if I choose, which is cool option. So, if you order one, be careful which year you get, they are different.

Vanne · 06-24-2021, 07:29 AM

AWESOME!!!!

Glad to hear you solved it Andre. A top spot of sleuthing there mate. congrats..

dre99gsx · 11-08-2021, 03:34 PM

Ok, need some feedback. In sim racing, I tend to move the bias to the rear right until I start to get the rear end to slide out from me on trail-braking, then back it off 1%. I have to keep up with the aliens...

Since the math says with MK60 MC I'm at 67% front / 33% rear, and Stock Z4M is 63% front / 37% rear, the math shows if I move to MK20 MC I can move my bias to 63% front / 37% rear, matching the Z4M.

Does this add up to you guys? I'm contemplating making the switch and see if I can improve braking just a bit more, but am worried of locking rears.

I don't know why Z4 3.0si from factor was 71% front / 29% rear.

06-14-2021, 02:24 AM	#45
Vanne Down Under!! 1621 Rep 4,294 Posts Drives: 2007 Z4MC Join Date: Mar 2013 Location: Dubai iTrader: (4)	hey Andre, have you seen/checked this??? its from an e86 coupe, non M. "I had the opposite problem where the DSC was constantly on! My preference is for ABS on and DSC off which I achieved by disconnecting the steering angle sensor. However, prolonged disconnection seems to cause a soft brake pedal so it's occasionally reconnected." i wonder if its the steering angle sesnor...?????? is yours disconnected? I am not sure how it causes soft pedal, but there you have it, maybe check it out. __________________ 2007 EuroSpec Z4///MC - Building/Developing Z4 GT3 Powered by Last edited by Vanne; 06-14-2021 at 02:30 AM..
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06-15-2021, 02:53 AM	#47
Vanne Down Under!! 1621 Rep 4,294 Posts Drives: 2007 Z4MC Join Date: Mar 2013 Location: Dubai iTrader: (4)	yeah, hes saying the diconnected steering angle causes soft pedal.. how? beats the shit out of me, but it does.. hes fixed it with a switch that he can momentarily turn on, once a day before track and then off again, and it all functions as it should, leave it disconnected for a period of time and whola..,. soft brake pedal.... hes got electric steering aswell.. no idea how, but thats what it is... __________________ 2007 EuroSpec Z4///MC - Building/Developing Z4 GT3 Powered by
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06-15-2021, 09:20 PM	#48
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	The internets is full of crazy theories.. https://rennlist.com/forums/993-foru...-abs-pump.html These guys have issues with ABS building some sludge that causes abs valves to stick, which is one way fluid could circulate/bypass internally and cause a sinking brake pedal. I may try flushing my entire system with denatured alcohol and use cheap dot3 to do testing. Running through SRF is getting hella expensive I did block off my calipers and sinking still occurs. Waiting on master cylinder but may have to buy another ABS/DSC module if I'm going to start throwing parts at it. Half of the people I've talked to say this is normal, the other half say it is not. What a crazy place to be in... __________________ Andre - 2J into a Z4 Coupe!
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06-16-2021, 07:31 PM	#49
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	UPDATE: Interesting. I blocked off the master cylinder with plugs. ROCK SOLID pedal even with 26in/hg vacuum applied to booster. So, MC checks out Ok. I hooked it back up to the ABS/DSC, then plugged all 4 output ports of the ABS. ROCK SOLID pedal, no drop. This leaves the lines -> calipers. Since I didn't see any leak in the calipers externally, this can only mean something between the ABS and caliper(s) is leaking and I cannot see it, or, the fluid is bypassing the caliper piston seals. Or, there is some stubborn air bubble in the caliper. Remember, stoptech trophies up front, 135i fixed calipers in the rear. Now I will connect one by one and see what I find. Hooked up the rear brakes, first left rear, then both. Pedal had a slight more slow drop but I would say about .5" in 10 seconds, it was almost nothing. I don't see the rear brake calipers/lines contributing. This now leaves the front lines/calipers. I connected driver caliper to ABS unit, everything else blocked off. Low and behold, the pedal starts slowly sinking. I then disconnected the caliper from the stoptech SS flex brake line and create a cap at the end of the banjo-bolt. I suspected the brake line was expanding. Nope. ROCK HARD pedal. So now this leaves me with the stoptech trophy caliper. It's funny, I've had nothing but unsatisfying brake feel ever since I swapped these bad boys in. I'm not sure what it could be, there is no fluid loss that can be found. Perhaps the two halves of the caliper are expanding from each other, but that would be a horrible design. I did put a solid block of metal between the caliper pistons to completely isolate the caliper, and watched it was someone else pressed the brake. I couldn't see anything from outside. It seems like the fluid could be weeping past the pistons seals. Going to call up stoptech or do more research. __________________ Andre - 2J into a Z4 Coupe! Last edited by dre99gsx; 06-16-2021 at 10:45 PM..
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06-17-2021, 08:02 PM	#50
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	Ok. I've reached a potential stopping point. Called stoptech, they just shrugged their shoulders and said "we don't know". So, I'm on my own here. I took the caliper apart, cleaned and rebuilt it. Actually tested it on the bench, each half separately. Both vacuum and 100psi + soapy water on the whole damn thing. I was going to even submerge it under water too. Both halves have no leak issues. I clamped the pistons on with a metal plate to keep them from moving. I went back to the car just to triple check - I have the brake line capped with an aluminum plug. Pedal is Rock solid. I hook up the caliper, bleed with a powerbleed, tappign with hammer, back and forth (inner and outer bleed screws). There is no air left I'm certain. Get back in the car, pump brakes, hold, and they start sinking. As they are sinking, I hear a "clink"... "clank" sound coming from the caliper, almost as if the immense pressure is straining the parts. But, I don't think it's related. Matter of fact, I even clamped both halves with a C-clamp on the outside just in-case the halves were pushing apart! No change. I'm starting to suspect this is some kind of design issue or like I mentioned in the previous post, the fluid is weeping past the piston seals just a tad bit, but not enough to leak out. Or, there is air trapped between the piston seals and the piston walls that never evacuates. I have no idea. I'm out of options. I may have to source another set of calipers and spend $, I think it's $800/ea for new ST40s with Z4M piston sizes. And if I chance it, buy them, and same issue, then I'm going to be upset and poor. __________________ Andre - 2J into a Z4 Coupe!
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06-17-2021, 08:12 PM	#51
inTgr8r Lieutenant General 2426 Rep 11,667 Posts Drives: M2 Comp Join Date: Mar 2006 Location: Toronto iTrader: (10)	wow..... just caught up on this thread again. Amazed that this is still unsolved! Sorry to hear that all the time & resources that you've poured into this haven't yielded a solution.
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06-18-2021, 07:44 AM	#52
Vanne Down Under!! 1621 Rep 4,294 Posts Drives: 2007 Z4MC Join Date: Mar 2013 Location: Dubai iTrader: (4)	Bloody hell mate, what a run around... At least youve come a hell of a long way isolating out parts that it /could/ have been. If pressure was dropping as fluid was going past the seals, then surely that would show..somewhere in a mess? __________________ 2007 EuroSpec Z4///MC - Building/Developing Z4 GT3 Powered by
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06-18-2021, 02:56 PM	#54
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	Correct, capped at the end of the flexible hose (banjo bolt), so I can verify the hoses themselves weren't flexing. I'm going to test that next - dial caliper on the brake caliper and measure flex/growth. Good call. No dust seals on the pistons, I can see directly if any fluid is weeping and possible going back into it's hiding spot. Clean as a whistle. I even left hoses on the nipples with some fluid to see if the fluid level moves up or down (or bubbles) when pressing brake pedal. Seems the bleeder screws are tight. I'm suspecting deformation now. I hear a "click" "clack" when doing this test, almost as if the aluminum caliper is deforming. I have another theory, and this one is starting to seem more plausible. For what it's worth, all of this work may help someone else who runs into this issue, so glad we're working on all possibilities. I looked up some things, Z4 and Z4M have different part numbers for vacuum booster and master cyl, but same ABS/DSC parts. So, if we assume the boosters are the same functionally (same assist per unit of vacuum), that leaves the master cyl. I’m still on the Z43.0si MC and booster. STR-40 kit w/355 rotors, 38/44 piston is what I currently have. Custom brackets to adapt them to Z4 3.0si knuckles. Z4M MC (same as E46 M3) master ports are 25.54mm fr / 20.65mm r, Z4M OEM front caliper piston 60mm, 345mm OEM rotor Z4 MC (same as E46 330i) master ports are 23.81mm fr / 22.2mm r, Z4 OEM front caliper piston 57mm, 325mm OEM rotor So Z4M has larger MC and larger OEM piston up front, larger rotor. Z4 has smaller for both. If Stoptech felt the Z4 3.0si 332mm kit with 30/36mm pistons was an appropriate swap to maintain displacement and bias, but instead I’m on 38/44 (and larger rotor) from the Z4M kit, I have 655 displacement increase which is quite large. I may be overpowering the Trophy caliper. Technically, if the 38/44 was meant for the Z4M, which has an even larger master cyl., I would guess that it would be even worse in that setup. Or, the much larger pistons mean a small amount of movement on the piston side (but normal for what the caliper would move to compress pads onto rotor) equals a much larger movement on the brake pedal size, exaggerating what I am experiencing? If so, It would make sense to move to a larger MC or smaller Trophy caliper piston group. If I upgrade to Z4M MC, it does change my fr/rear bias (more front, less rear) and I purposely wanted more rear for my driving style. So, I would have to do the math to see what I would lose. Will get back to you with more tests. A buddy of mine is letting me try his trophy caliper as another data point. __________________ Andre - 2J into a Z4 Coupe!
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06-18-2021, 10:35 PM	#55
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	Just tested a 6-piston Trohpy caliper from an Audi RS4. This has 36,34 and 30 mm piston sizes. Do the math, total of 2630mm2 surface area. My Z4M calipers of 38 and 44 = 2650mm2. Roughly the same. This caliper exhibited the same pedal dropping, which now makes it obvious that 3 calipers can't be air in system or a faulty caliper (or even design). I've driven this Audi at the track with this trohpy kit and the brakes are amazing. His car does not have this pedal drop issue either. Next up is an E46 M3 master cylinder. Should have a result from that soon on whether going larger front bore size reduces the pressure exhibited on the caliper at the amount of pressure my leg can supply. I do have to make a correction, the M3 MC has larger front bore size, which should reduce front pressure, but smaller rear bore size than my Z4 MC, which should increase rear pressure. This should move my brake bias further back, and that would be Ok. I can drop my rear pad co.friction and compensate if needed. I just hope that I don't then introduce this issue now to my rear calipers __________________ Andre - 2J into a Z4 Coupe!
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06-19-2021, 03:22 PM	#56
wdb dances with roads 4717 Rep 4,094 Posts Drives: '07 E86, '02 996, '95 Seven Join Date: Jul 2015 Location: the perimeter iTrader: (4)	Phenomenal detective work.
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06-20-2021, 11:10 AM	#58
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	You're right in that the Z4 is closer 1:1, but the rotor sizes and Z4 caliper piston sizes are different as well to the Z4M, thus there are a few more variables there.. If I'm pushing down 100lb with my leg on the brake, my end goal is to reduce the distance the caliper piston moves per inch of leg travel. I want to make the front brakes weaker. Another way to put it, I want to NOT be able to flex the front caliper with 100lb of leg force. So, I can either go to smaller caliper piston sizes, or larger MC bore size. I may already have too much front bias with my current system. A larger MC bore size will move the same amount of fluid but at (less distance) at the same leg pressure Pascal 100lb leg force on pedal 1" pedal travel Z4 MC Pressure=F/Area 100/445(z4 MC area) = .224 PS Stoptech caliper piston Force = Pressure * Area .224 * 2653(stoptech pistons area) = 596lb. So, 100lb leg force creates 596lb caliper force Now the bigger bore Z4M MC Z4M MC Pressure=F/Area 100/512(z4M MC area) = .195 PS Stoptech caliper piston Force = Pressure * Area .195 * 2653(stoptech pistons area) = 518lb. So, 100lb leg force creates 518lb caliper force Less force created at the same leg pressure. You can also calculate the distance move at the caliper. Z4 -> 4451" / 2653 = .167" Z4M -> 5121" / 2653 = .192" What this means is at 100lb leg pressure, the front pistons will have less force at the same distance traveled. But, the rear pistons will have greater force because the MC rear bore size goes in reverse, so I am moving the bias back probably by quite a bit. The 335I front calipers had a 57mm diameter, and the Z4 has a 57mm diameter piston. They were exact matches in the regards, but of course I was using different rotor sizes anyway. I was on the 345mm Z4M rotor with the 335i caliper. I'm on a 355mm rotor with the Stoptech caliper. So: 345mm rotor, 2437mm2 vs 355mm rotor, 2653mm2. Probably more significant front bias between the two there... Will find out soon enough when I receive the Z4M MC if the math checks out! lol If this all works out, I'll need to be careful on the track with too much rear bias. I can downgrade the rear pads a bit since I'm on PFC08. I can go to the stoptech sports perhaps with less Co.Friction. 135i rear piston is 42mm and I have Z4M rear rotor (328mm) , Z4 stock piston is 40mm (294 rotor), so I've already increased the rear braking advantage by quite a bit. Attached a worksheet, I think I have all the OEM numbers correct. If the math is accurate, I'll be moving from 70/30 to 67/33 bias. Feel free to verify! Attached Images __________________ Andre - 2J into a Z4 Coupe! Last edited by dre99gsx; 06-20-2021 at 12:44 PM..
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06-21-2021, 05:41 AM	#59
Vanne Down Under!! 1621 Rep 4,294 Posts Drives: 2007 Z4MC Join Date: Mar 2013 Location: Dubai iTrader: (4)	Hmm.. lemme get my pop-corn.... Andre, your saying that your over-servo-ing the front brakes and thats why your getting pedal drop because your deforming the front calipers? doesnt really sound plausible mate, but easily tested, remove the vacuum line from the brake booster... see what happens... i also highly doubt that if you /ARE/ deforming the caliper, that its elasticity is such that it returns to its original state before deformation.. (especially if you consider how many times youve done this per lap) anyhows, ill wait to see how you get on with your latest findings. fingers crossed. __________________ 2007 EuroSpec Z4///MC - Building/Developing Z4 GT3 Powered by Last edited by Vanne; 06-21-2021 at 05:53 AM..
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06-23-2021, 05:45 PM	#62
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	BOOM... problem solved. MK60 E46M3 2003-2007 MC with 25.54 front port / 22.2mm rear port (vs my Z4 23.81mm front port / 22.2mm rear port) swapped in, and pedal does not sink to floor. It all makes sense. I had too much pressure going to front calipers at 70%front/30% rear ratio after all the calculations. I am now 67% front/33% rear (theoretically). I learned a valuable lesson. Sorry for dragging you all along on this. Port matching / piston matching is very important if you are doing any brake upgrades. This doesn't solve the pad-knockback issue, although I won't know until I hit the track, but hopefully this gives me the consistent pedal I've been missing for years. Will report back on how it feels at the track. The other unknown is this Dorman MC M630897 I purchased (not the BMW OEM unit). I did call up dorman and they confirmed the port sizings, but who knows if this thing will survive track duty. I know this is being cheap but whatever... Thanks for all the help on here. __________________ Andre - 2J into a Z4 Coupe!
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06-24-2021, 07:29 AM	#65
Vanne Down Under!! 1621 Rep 4,294 Posts Drives: 2007 Z4MC Join Date: Mar 2013 Location: Dubai iTrader: (4)	AWESOME!!!! Glad to hear you solved it Andre. A top spot of sleuthing there mate. congrats.. __________________ 2007 EuroSpec Z4///MC - Building/Developing Z4 GT3 Powered by
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11-08-2021, 03:34 PM	#66
dre99gsx Captain 508 Rep 911 Posts Drives: 1994 Toyota Supra Join Date: Aug 2011 Location: NJ iTrader: (2)	Ok, need some feedback. In sim racing, I tend to move the bias to the rear right until I start to get the rear end to slide out from me on trail-braking, then back it off 1%. I have to keep up with the aliens... Since the math says with MK60 MC I'm at 67% front / 33% rear, and Stock Z4M is 63% front / 37% rear, the math shows if I move to MK20 MC I can move my bias to 63% front / 37% rear, matching the Z4M. Does this add up to you guys? I'm contemplating making the switch and see if I can improve braking just a bit more, but am worried of locking rears. I don't know why Z4 3.0si from factor was 71% front / 29% rear. __________________ Andre - 2J into a Z4 Coupe!
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