My new StopTech/Apex setup on 128i

[jafo1701]

Originally Posted by dcaron9999

I suppose there is no way to do this with the brake line under pressure and caliper and still on the car, but off the caliper bracket? Do the pistons easily come out - how are they held in - can they be screwed out?


You did get the CT pads extremely fast. Congrats! I was told by another vendor that the 135i caliper pads were not in stock at the Carbotech warehouse, and 3-5 biz days were needed to produce them.

Please post back your results once you hit the track with XP12 pads - really looking forward to your review! Have you had fitment issues - do the CT XP pads fit loosely in the caliper, and does the brake sensor cutout have paint and glue stuck in it (not that it matters on a race pad but do the XP12 even have the cutouts)?

I swap pads so much that I don't even use the brake sensors. From past experience with the 10s on the front they don't fit. I didn't even try to attach the rears as all my sensors are zip tied up out of the way. There are cutouts on the 12s, I didn't try em though. There is no rattle on the 12s. I do use the stock backing plates though. I'll report back on Tuesday with results.

[nate340]

Alright so another track day done, so for whatever reason it took quite a while to boil my brake fluid yesterday 15-20min of hard fast lapping instead of the normal 5 laps. Which makes me think this might be a vapour lock issue as it’s the only thing that’s changed since last time out on track.

The ambient temps were around the same 20C as other events.

I also realize that I’m one of the few running BFG R1’s which are pretty much a full racing slick which means I’d put more temp into my brakes compared to everyone else that run just a performance street tire on track.

I did however experience the HP+ pad fade that I’ve heard so much about but it happened well after my fluid had boiled. I’ll be moving to at DTC 70 sometime in the near future.
So assuming that HP+’s start to fade at a consistent temp no matter what car they’re on why is my brake fluid boiling before pad fade while it seems everyone else run into pad fade before they boil they’re brake fluid?

I’m considering taken the car to a BMW Dealership as I’ve heard they’re the only ones that are able to activate the stability control valves to force any air that might be trapped in the stability control system.

Also since I bought the car used I’m unsure what the past owner may have done to the brake system. I’d really appreciate if another 135i owner would go out to their car pump the brake pedal a few times till its rock hard and then just see if the pedal slowly sinks? I’m unsure if this is normal or if my car has an issue, thanks in advance it should only take you a few minutes and would save me a lot of time pondering.

[jafo1701]

Nate. I tried the brakes for you and it goes firm and stays firm and doesn't sink. If I release it the pedal is nice and firm and feels normal. Hope that helps

[fe1rx]

Originally Posted by nate340

Alright so another track day done, so for whatever reason it took quite a while to boil my brake fluid yesterday 15-20min of hard fast lapping instead of the normal 5 laps. Which makes me think this might be a vapour lock issue as it’s the only thing that’s changed since last time out on track.

The ambient temps were around the same 20C as other events.

I also realize that I’m one of the few running BFG R1’s which are pretty much a full racing slick which means I’d put more temp into my brakes compared to everyone else that run just a performance street tire on track.

I did however experience the HP+ pad fade that I’ve heard so much about but it happened well after my fluid had boiled. I’ll be moving to at DTC 70 sometime in the near future.
So assuming that HP+’s start to fade at a consistent temp no matter what car they’re on why is my brake fluid boiling before pad fade while it seems everyone else run into pad fade before they boil they’re brake fluid?

I’m considering taken the car to a BMW Dealership as I’ve heard they’re the only ones that are able to activate the stability control valves to force any air that might be trapped in the stability control system.

Also since I bought the car used I’m unsure what the past owner may have done to the brake system. I’d really appreciate if another 135i owner would go out to their car pump the brake pedal a few times till its rock hard and then just see if the pedal slowly sinks? I’m unsure if this is normal or if my car has an issue, thanks in advance it should only take you a few minutes and would save me a lot of time pondering.

If you are running HP+ you are not putting more heat into your brakes than everyone else regardless of your tire. These pads fade well before say a DTC 70. By pad fade you mean the pedal is hard but the braking effect is reduced, right?

Your brake fluid can't boil before your pads fade, because when your fluid "boils" (fluid fade) the pedal goes to the floor with no pressure going to the pads and so no friction (or further heat) being generated. What exactly do you mean when you say your fluid is boiling?

If you have air in your hydraulics, the pedal will be soft all the time, so that isn't likely your problem.

HP+ are barely adequate for lapping with a street tire and completely inadequate for lapping with an R-compound tire.

Opinions differ widely on the fluid front, but my experience has led me to using Castrol SRF and nothing else, flushing it once a year. It seems expensive but isn't if you can avoid multiple flushes.

In my experience, once a fluid is overheated, it is never right again and should be flushed. It will recover once it cools, but not completely. How much effort do you expend in cooling your brakes after a lapping session. If you come in and park with your pads stinking hot (literally) and just park, you are abusing your fluid. If you really are overheating your fluid every lapping day, you should be flushing it after every lapping day.

If your pedal is getting a bit soft or the travel is getting a bit long but not going to the floor, there are other (than fluid fade) possible explanations, including pad knockback and thermal deformation of your shims (if you are using them). Shims may help with thermal isolation but they don't help when it comes to a firm pedal.

What track are you at? Is it particularly hard on brakes? When you don't have brakes that can take anything you can throw at them (and you don't) you have to manage them as a limited resource. Examples:
- limit the number of hot laps
- alternate hard laps with cool-off (minimal braking) laps
- brake earlier
- brake less
- don't make every lapping day an experiment to find out how quickly you can fade your pads/fluid

[dcaron9999]

Originally Posted by jafo1701

I swap pads so much that I don't even use the brake sensors. From past experience with the 10s on the front they don't fit. I didn't even try to attach the rears as all my sensors are zip tied up out of the way. There are cutouts on the 12s, I didn't try em though. There is no rattle on the 12s. I do use the stock backing plates though. I'll report back on Tuesday with results.

After reading your comment, Im embarrassed to admit that I have been running without stock backing plates, which explains the pads moving about and clunking sounds.

Fixed that this evening, while I was in there to remove the glazing on my XP10 pads and check the state of my pistons and dust boots. Clunking sound is now gone, thanks to you!

[dcaron9999]

Originally Posted by fe1rx

From my OHLINS post: ... BRAKE INSTALLATION AND BRAKE PISTON BOOT REPLACEMENT ...

Thanks for this!

[nate340]

Originally Posted by jafo1701

Nate. I tried the brakes for you and it goes firm and stays firm and doesn't sink. If I release it the pedal is nice and firm and feels normal. Hope that helps

Thanks I'm now aware my braking issues are most likely related to this.

Originally Posted by fe1rx

HP+ are barely adequate for lapping with a street tire and completely inadequate for lapping with an R-compound tire.

If you are running HP+ you are not putting more heat into your brakes than everyone else regardless of your tire. These pads fade well before say a DTC 70. By pad fade you mean the pedal is hard but the braking effect is reduced, right?

The reason I’m using HP+’s is that I received 3 sets of them for free but I do plan to move to something more track orientated.

Originally Posted by fe1rx

Your brake fluid can't boil before your pads fade, because when your fluid "boils" (fluid fade) the pedal goes to the floor with no pressure going to the pads and so no friction (or further heat) being generated. What exactly do you mean when you say your fluid is boiling?

When brake fluid starts to boil the pedal starts to sink, the more air in the line the further the pedal sinks. Lap after lap my brake pedal sinks further and further down. It will eventually go to the floor. What I’m doing is using my left foot to pump the brake pedal down the straight to build pressure in the brake lines so that when I do arrive at the braking zone I have enough pressure to brake adequately and after doing this for a bit my pads begin to fade (brake pedal firm yet applying a lot of brake pressure while not slowing down at the typical corresponding amount.)

Originally Posted by fe1rx

If you have air in your hydraulics, the pedal will be soft all the time, so that isn't likely your problem.

Opinions differ widely on the fluid front, but my experience has led me to using Castrol SRF and nothing else, flushing it once a year. It seems expensive but isn't if you can avoid multiple flushes.

In my experience, once a fluid is overheated, it is never right again and should be flushed. It will recover once it cools, but not completely.

Once I have a track event and boil my brake fluid the pedal does remain fairly soft until I bleed the brakes and I always see significant air coming out of the calipers.

I’m flushing my brake fluid at every track event using Motul RBF 660 which allows me to run significantly longer before running into my brake issues when compared to ATE Super Blue, since moving to a fluid with a much higher boiling point significantly helped my brake issue I assumed it's vapour lock caused by overheating and boiling my brake fluid.

Originally Posted by fe1rx

How much effort do you expend in cooling your brakes after a lapping session. If you come in and park with your pads stinking hot (literally) and just park, you are abusing your fluid.

Before I bring my car into the pits I take two cool down laps if I’m unable to properly cool my car before bringing it into the pits the pedal does sink straight to the floor when I return to the car to go back out on track.

Originally Posted by fe1rx

If your pedal is getting a bit soft or the travel is getting a bit long but not going to the floor, there are other (than fluid fade) possible explanations, including pad knockback and thermal deformation of your shims (if you are using them). Shims may help with thermal isolation but they don't help when it comes to a firm pedal.

I may be having pad knockback as I do recall once or twice that my pedal is suddenly firm while at the last braking zone it was very soft. I’ll have to look more into it and keep a close eye on it next time out on track. I am running titanium shims which seemed to help a reasonable bit but am willing to remove them and see if it helps.

Should i be running the stock steel backing plates along with the titanium shims? As right not i’m only using the titanium shims.

Originally Posted by fe1rx

What track are you at? Is it particularly hard on brakes? When you don't have brakes that can take anything you can throw at them (and you don't) you have to manage them as a limited resource. Examples:
- limit the number of hot laps
- alternate hard laps with cool-off (minimal braking) laps
- brake earlier
- brake less
- don't make every lapping day an experiment to find out how quickly you can fade your pads/fluid

The track where it is most noticeable is TMP Toronto Motorsports Park in Cayuga. I have 3 Major brake zones with the most significant being 190KPH down to 110

I’m currently trying to resolve the issue so that I’m able to push harder and enjoy more track time without having to run cool off laps every few laps.

[fe1rx]

Originally Posted by nate340

When brake fluid starts to boil the pedal starts to sink, the more air in the line the further the pedal sinks. Lap after lap my brake pedal sinks further and further down. It will eventually go to the floor. What I’m doing is using my left foot to pump the brake pedal down the straight to build pressure in the brake lines so that when I do arrive at the braking zone I have enough pressure to brake adequately and after doing this for a bit my pads begin to fade (brake pedal firm yet applying a lot of brake pressure while not slowing down at the typical corresponding amount.)

Once I have a track event and boil my brake fluid the pedal does remain fairly soft until I bleed the brakes and I always see significant air coming out of the calipers.

I’m flushing my brake fluid at every track event using Motul RBF 660 which allows me to run significantly longer before running into my brake issues when compared to ATE Super Blue, since moving to a fluid with a much higher boiling point significantly helped my brake issue I assumed it's vapour lock caused by overheating and boiling my brake fluid.

Your description of being able to pump up the brakes and getting a reasonably firm pedal when you do is not consistent with fluid fade.

Titanium shims are good for the fluid in that the insulate the caliper a bit, but they are bad for the pad because the pad loses some ability to dissipate heat. Running the stock shim as well is a good idea because it eliminates the rattle because it wraps around the ends of the pad to take up the end clearance. That said, true race pads get hotter and expand more so may need additional clearance. For that reason I use custom made stainless shims that only wrap around the thrust end of the pad. Stock shims should be ok on HP+ though. Some knockback may be a result of the pads rattling about. I would say it is worth trying the stock shims in addition to the titanium ones. Don't use any brake compound between the shims and the pads though. It just makes a mess at the temperatures you are running.

I would love to know how pads distort due to thermal stresses. Any temperature differential across the thickness will introduce a bending tendency, which will knock your pistons back. It may actually be worth trying running without the titanium shim to see if it helps in this regard.

I assume you are bleeding your brakes the conventional way (pumping the pedal)? Much (maybe all) of the air you see when you bleed may actually be air being drawn in around the bleeder screw threads. Try pulling the bleeder screws out and putting some anti-seize on the threads to act as a sealant. Even better if you are bleeding your brakes often is to use a speed bleeder screw. These have a fairly long lasting sealant on the threads and have a check valve built into them. You don't need to close the bleeder screw between pumps which also means you can do the bleeding by yourself. Another trick is to use a short length of rubber hose (e.g. fuel line) pushed on the end of some clear pvc tubing as a bleeder hose. The rubber hose is more resilient and it seals better on the bleeder screw. If your bleeder bottle is below the caliper, once the line is full the suction created by the siphon effect will draw air into the bleed line if there is any possible air leak around the screw threads. You can also reduce this by keeping the bleeder bottle above caliper height. When you are pumping the brakes to bleed, do it slowly and release the pedal slowly to reduce fluid turbulence and to reduce any suction forces in the fluid.

Fluid boiling produces fluid vapour, not air, and when the fluid cools the vapour should condense. The only place air can truly come from is by being drawn in past the piston seals, which is unlikely. Often what people think is air in the system actually comes from the reason noted above. Fluid that has been cooked does become more compressible though, which is presumably due to some kind of chemical decomposition in the fluid. If you are seeing the fluid that you are bleeding being discoloured in some way, it definitely points to some kind of decomposition. For a track bleeding you don't need to flush the whole system. You just need to get the old fluid out of the calipers. Maybe 4 pumps on each of the rear calipers just because, then half a bottle of fluid out of each of the front calipers. Because the fluid in the caliper is replaced by progressive dilution, you need to bleed out several times the volume contained in the caliper to fill it with mostly fresh fluid.

I hope this is of some assistance.

[nate340]

master cylinder failure seems to be the issue.thanks for all the advice.

[wjk_glynn]

Originally Posted by nate340

I may be having pad knockback as I do recall once or twice that my pedal is suddenly firm while at the last braking zone it was very soft.

I've experienced this with my Stoptech BBK, along with a minor version on the street where there is a small amount of variability in brake pedal travel/pressure from application to application. Sometimes it's rock hard, sometimes there's a small bit of squish... And this happens from block to block, during regular driving around town.

The shop I take the car to is very reputable (they even race their own 135i) and I trust their work. The wheel bearings are good, the brakes were bled a few times with Endless RF-650 fluid, etc...

They said it's the classic symptom of knockback, but I'm struggling to believe that I could get hints of that at 35-40 mph surburban driving.

It should be noted that on test drives, they don't see (or more accurately feel) this issue. These are good & experienced guys. But I swear that minor variability is still there for me. My Land Rover LR3 and VW Passat have more consistent brake feel around town, and I don't recall the variability with the 135i OEM setup.

And then you said...

Originally Posted by nate340

master cylinder failure seems to be the issue.thanks for all the advice.

So I gotta know more, please tell...

Thanks.

Karl.

[nate340]

It’s a pretty easy test to perform, with the car on but stationary repeatedly push the brake pedal if it slowly sinks further and further towards the floor my understanding is it’s the master cylinder. I can’t quite get it to the floor but it’s certainly sinking and not returning to the usual height. I imagine once everything is really hot and in a demanding brake environment it’s much worse, whether that’s on track or in stop and go traffic. Fluid starts leaking around the piston in the master cylinders instead of applying pressure to the calipers.

I’ve yet to replace the master cylinder it’s only $300 from ECS Tuning but I’m unsure if I’ll have BMW install or attempt to do it myself. I’ll call them Monday and see what they’re asking.

My car is a 2009 135i with 191 000KM mostly highway. But I have tracked it 15+ events in the last 18 months. I just didn’t think a car that’s this relatively new would have such issues yet.

I’ll update the thread once it’s replaced.

[fe1rx]

Originally Posted by nate340

It’s a pretty easy test to perform, with the car on but stationary repeatedly push the brake pedal if it slowly sinks further and further towards the floor my understanding is it’s the master cylinder. I can’t quite get it to the floor but it’s certainly sinking and not returning to the usual height. I imagine once everything is really hot and in a demanding brake environment it’s much worse, whether that’s on track or in stop and go traffic. Fluid starts leaking around the piston in the master cylinders instead of applying pressure to the calipers.

I’ve yet to replace the master cylinder it’s only $300 from ECS Tuning but I’m unsure if I’ll have BMW install or attempt to do it myself. I’ll call them Monday and see what they’re asking.

You can't realistically replace it yourself because you will not be able to bleed the ABS unit.

I suspect your diagnosis is wrong. Heat won't make its way to the master cylinder so it has no effect on the master cylinder operation.

You should press and hold the brake pedal once, using the maximum brake pressure that you normally need to apply (not using all your weight). If the pedal slowly sinks over say 15 seconds, without increasing the applied brake pressure, you may be right. A sinking pedal is different from a long pedal. A sinking pedal points to internal bypass around the master cylinder seal, or an external leak. A long pedal points to increased clearances (e.g. due to knockback or thermal expansion effects) that must be taken up with fluid volume before the pedal gets hard.

I see some variability in my pedal at the track. Ideally there wouldn't be any, but what you are seeing may be "normal" and you may just be gun shy because of your earlier brake problems.

The dealer should be able to objectively diagnose the master cylinder, but don't be surprised if they say it is ok.

[nate340]

it's a possibility I may be wrong, hopefully i'll know within the next couple of weeks. The issue is slight but it defiently sinks not long but sinks, it's why pumping the pedal works on track. i'm unsure what BMW will say but at the end of the day i have a few options spend the $300 and install it myself I've done it in the past with ford vehicles with DSC. I'm aware technically you're supposed to bleed the system opening all the control valves but usually isn't necessary with no noticeable air in the system. failing which i could always take the car to BMW and ask them to bleed the system. As of now I'm hoping BMW will recognize the issue and be happy to do the work.

[nate340]

also while on track everything in the engine bay is much hotter than on the street but do think having to to brake hard again and again in short succession is causing the issue.

[jafo1701]

I thought I would give everyone an update on the brakes and my last track day. The Carbotech XP 12s held up fine up front. I felt I was just as hard on the brakes as the previous week. XP 10s in the rear of course no problem. I had no brake fade or boiling fluid problems. Overall a good track day, although I was a bit under the weather the whole day, so I wasn't at my best. Still a fun day, I was a bit slower then the prior week. I attribute that to the way I felt and the number of cars in our run group. There were about double the amount of cars as the previous week. So on almost all the laps I was being passed or passing someone. Plus we had 3 Black Flags that brought everyone in out of the 5 sessions that I did.

[dcaron9999]

Originally Posted by jafo1701

I thought I would give everyone an update on the brakes and my last track day. The Carbotech XP 12s held up fine up front. I felt I was just as hard on the brakes as the previous week. XP 10s in the rear of course no problem. I had no brake fade or boiling fluid problems. Overall a good track day, although I was a bit under the weather the whole day, so I wasn't at my best. Still a fun day, I was a bit slower then the prior week. I attribute that to the way I felt and the number of cars in our run group. There were about double the amount of cars as the previous week. So on almost all the laps I was being passed or passing someone. Plus we had 3 Black Flags that brought everyone in out of the 5 sessions that I did.

Thanks for your feedback. This is likely my next setup as well. Replacing the XP10's in the front with XP12's, and keeping my XP10 in the back.

Thought I would ask, do you drive with DSC OFF (TIMYOYO mode) on the track, and do you think DSC might be using your brakes in addition to your input, therefore overheating more rapidly? Just thought about this today, from feedback from guys at the track. Might have to try turning DSC off next time, once my car and tires are warmed up, to see if my brakes last longer and my lap time is reduced ...

[jafo1701]

Originally Posted by dcaron9999

Thanks for your feedback. This is likely my next setup as well. Replacing the XP10's in the front with XP12's, and keeping my XP10 in the back.

Thought I would ask, do you drive with DSC OFF (TIMYOYO mode) on the track, and do you think DSC might be using your brakes in addition to your input, therefore overheating more rapidly? Just thought about this today, from feedback from guys at the track. Might have to try turning DSC off next time, once my car and tires are warmed up, to see if my brakes last longer and my lap time is reduced ...

Unless it's raining. I turn everything off. I usually don't even run in the rain though. Not worth it in my opinion.

[eviled]

Well, I just had a late reaction to a red light at a decent clip and notice my brakes felt less impressive then they use to be. I'm looking into replacements. I don't track my car and all I know is the OEMs were pretty damn good. Questions...

Do y'all recommend "turning" the rotors at 66k miles or just getting new ones? I don't want slotted or drilled, but I do like the looks of the black painted centers, because mine are all corroded . As for pads, I only ask for them to be at least as good as new, or better but with less dust. The OEMs are good for exactly 2 hours of driving before the wheels are covered.

Suggestions?

[nate340]

finally had some good track time and it was master cylinder failure that caused my braking issues. i replaced the master cylinder by myself and now have a nice firm pedal while on track. the car had 195 000KM on it when the master cylinder started to fail. If anyone has any questions feel free.

[bNks334]

Originally Posted by nate340

I may be having pad knockback as I do recall once or twice that my pedal is suddenly firm while at the last braking zone it was very soft. I’ll have to look more into it and keep a close eye on it next time out on track. I am running titanium shims which seemed to help a reasonable bit but am willing to remove them and see if it helps.

Just thought I'd add to this thread that the car pretensions the brakes if you lift off the gas quickly. Even in street driving you may notice that in panic situations the brake pedal is nice and firm when you switch from the gas to the brakes.

Only way to get a consistent feel would be to code this off and then see how they feel.

The car also performs its own brake fade compensation. Brake pressure is increased as the car estimates brake temperatures. Code that off too to get a more consistent pedal feel.