Question about brake setups for those of you with 24v motors...

[dude8383]

So this season has had many ups and unfortunately many downs too.

Some of you might have seen my posts before about my troubles with my brake setup. I think that yesterday was the last straw for me.

But first, a bit of background on my setup.

I'm running Massive's street kit, the 280x22 setup with Meyle blanks that 2002maniac so graciously supplies (since there aren't many other alternatives). I am also running a 7 series master cylinder.

Ever since I started using this setup I noticed that I'd burn through a set of pads in one day no problem. Previously it was dependent on the track... this season not so much. I would run the pads all the way down to their backing plate without issue but still... one track day?! I tried PFC 01's, HT-10's, ST-41's (just tried these), and Wilwood Compound H's up front. None of these lasted me more than one day.

For reference I've been to: Lightning, Watkins Glen, Summit Pt Main, Shenandoah, LRP and Thunderbolt.

My last event at Lightning I experienced severe juddering under heavy braking. Pedal stayed nice and firm though. Also, my rotors were glowing red, almost like a proper race car...



After the event I inspected the rotor and noticed that there was heavy grooving... a friend suggested it might be air trapped in the system causing this. Curious what you guys think about this as well.

Front brake temps exceeded 600F and rears were around 200-300 range. Oh and I removed the front backing plates to help with cooling...

So I was at Thunderbolt yesterday and I took the precautionary measure of replacing the seals on my Wilwood calipers. I thought that after about 17 days of track use on em, it was time to replace them. Fairly simple on these calipers so why not?

Anyway, after about 20 min of lapping the pedal would start to drop to the floor, a quick pump and I'd have pedal pressure again. I pitted, bleed the system and then went back out... again, after 20 min (or less) the same symptoms would come up. I did this three times and just got fed up with constantly having to bleed the system in order to get a 20 min session :( One last observation. I hit ABS a few times while braking and soon thereafter the pedal would start to act funny. Air still in the system??

Front rotor temps were above 600 but the rears this time were around 420-440. I ran ST-41 pads up front and PFC 01's in the back.

I don't know what to do at this point... If I go with a larger caliper up front I will most certainly have to get something for the rear. The question is, does it make sense to go that route?

I'm debating whether or not I should consider sourcing e30 m3 5 lug components (almost impossible but time is on my side) or get the E36 M3 stuff up front and something decent in the back (m coupe, 318ti?).

No one at the track has these problems... its driving me mad having to constantly worry about this shit when I'm out there on the track. When the brakes work its great, but when they don't I lose confidence in the car.

So what say you fellow track heads?

[evandael]

this is largely conjecture, but..

i don't believe you'd gain anything from the e30 m3 components over your current setup. the front rotors are the same diameter and only 3mm thicker, so you'd gain very little thermal mass to help with the temps. that and the fact that the cast-iron single piston sliding calipers would be a downgrade from the aluminum 4 piston monoblocks.

swapping to e36 m3 would add a lot of weight and some people claim to never sort out the caster issues. additionally, it would end up far more front biased with only 318ti rears, so z3m rear components would really be the best bet but now you're looking at all new TA's, halfshafts, output flanges... the costs really start adding up.

it sounds like there is air trapped in your system, perhaps in the ABS pump. then with your scorching hot front rotors, the fluid boils and the pedal drops.


i think that trying out some higher quality front rotors (any old G60 corrado, correct? with the requisite small amount of machine work, of course), bleeding the shit out the system, sourcing some serious pads, and rigging up some brake ducts would be a cheaper way to fix the issue.


good luck and let me know. i am planning on running effectively the same setup on my s52 car and want to track it occasionally.

[smahala1286]

Do you have brake ducting? Sounds like you have air trapped in the ABS unit.

[dude8383]

this is largely conjecture, but..

i don't believe you'd gain anything from the e30 m3 components over your current setup. the front rotors are the same diameter and only 3mm thicker, so you'd gain very little thermal mass to help with the temps. that and the fact that the cast-iron single piston sliding calipers would be a downgrade from the aluminum 4 piston monoblocks.

swapping to e36 m3 would add a lot of weight and some people claim to never sort out the caster issues. additionally, it would end up far more front biased with only 318ti rears, so z3m rear components would really be the best bet but now you're looking at all new TA's, halfshafts, output flanges... the costs really start adding up.

it sounds like there is air trapped in your system, perhaps in the ABS pump. then with your scorching hot front rotors, the fluid boils and the pedal drops.


i think that trying out some higher quality front rotors (any old G60 corrado, correct? with the requisite small amount of machine work, of course), bleeding the shit out the system, sourcing some serious pads, and rigging up some brake ducts would be a cheaper way to fix the issue.


good luck and let me know. i am planning on running effectively the same setup on my s52 car and want to track it occasionally.

Valuable advice. The thing is that the E30 M3 guys don't burn through a set of front pads in one day... then again they're probably not going as fast as my s52 powered car is. Additionally, the rear rotors are 282mm vs 258 on the 4 lug. The rear I think would help balance things out a bit more.

The problem that I have is having to modify rotors each time. At the track if I suffer a failure... the chances of one of the track guys having a spare part are close to NIL. Pack extras I know... but I don't trailer the car, I drive to and from these events. I can't pack everything lol.

I believe that the pads I have already sourced are about serious as it gets... Carbotech's are a step up I think... but they're like 190-ish for a set. I don't really feel like burning through that much money in one track event. I've already dropped at least 7 bills in brake pads alone. Is there a way for me to cycle the abs pump to try and get the air out? Its mighty expensive flushing a system with Motul... at $16 a bottle its a tough pill to swallow. Unless I use standard DOT 4 shit that you can get at the local parts store?

Brake ducts are certainly an option and definitely a much cheaper alternative. There isn't much info out there with respect to brake setups for 24v guys that track their cars.

Do you have brake ducting? Sounds like you have air trapped in the ABS unit.

No on the brake ducting, but how do I get air out? The abs pump is off when I bleed the brakes... anyway to engage it?

[dude8383]

And here's Heinrich schooling me:

http://forums.bimmerforums.com/forum/showpost.php?p=24298191&postcount=14

E30 M3 stuff should be up to the task... which is why I had considered it.

[FredK]

Yes, E30 M3 stuff should definitely be up to the task. I am not as experienced as you are, and have street tires, but I had no problems with 2 days at WGI this year. I was not pushing it hard, and I'm at around 135 before the bus stop. My HT-10 pads barely wore, though it was probably around 65 degrees outside.

I don't think the E30 M3 stuff is anything special, as Evan pointed out, but it does have fairly sizeable pads both in area and thickness, unlike the Dynalites.

[NigelStu]

I would expect that you are having some over-heating issues with the brakes, which is creating elevated wear rates. Get some ducting to them. With the extra speed, there is a LOT more kinetic energy those brakes have to deal with. More energy, more heat.

How / when are you measuring the rotor temps? infared pyrometer after you get back to the pits is only a vague indicator. There are some temperature paints/stickers that will tell you in-use temps. Make sure the pads are up to the task of the heat the system is putting out.


Grooved rotors = aggressive pad compounds chewing up hot rotors. Possibly combined with the backing plate / rivets holding the brake compound onto the backing plate (if that is the style being used by those brake manufacturers) that are contacting the rotor as you wear the pads all the way down. Some pad compounds are worse than others for rotor wear.

It does sound like you still have some air trapped in the system somewhere, ABS unit is a good bet. Although I can't help you out with how to activate the ABS pump while bleeding. (Hopefully someone here does, cuz I'd like to know!).

You could also be getting some pad-knock-back, which can occur if running over rumble strips, long sweepers, quick transitions and off-track shenanigans. This can become more apparent as the pads wear down.

[JRKOUPE]

I just gotta think something is not right......I mean , to go thru pads in one day just screams "something is up". I know the pads are kinda thin,..... I run the same set up.....but still.

Ive only run the set up one day w/ my s50, and I was running kinda ez w/ HG issues....I wish I had more insight.

good luck....

keep us posted.

to have to go 5 lug is an expense neither of us want Im sure.

[dude8383]

Yes, E30 M3 stuff should definitely be up to the task. I am not as experienced as you are, and have street tires, but I had no problems with 2 days at WGI this year. I was not pushing it hard, and I'm at around 135 before the bus stop. My HT-10 pads barely wore, though it was probably around 65 degrees outside.

I don't think the E30 M3 stuff is anything special, as Evan pointed out, but it does have fairly sizeable pads both in area and thickness, unlike the Dynalites.

Not sure I'm as experienced, I've only got like 18 track events under my belt lol.

Yup, I'm hitting around 135 before bus stop as well, I managed to get two days from my HT-10's there last year... and that was still with the backing plates. But like you said, temps were cooler when I was there as well.

The 12mm pad is definitely a let down though, I wish there was a bit more meat on em. The next step up with Massive is an 18mm pad with the 300x22 kit. Oddly enough I think my HT-10's had the best wear out of all of them.

I would expect that you are having some over-heating issues with the brakes, which is creating elevated wear rates. Get some ducting to them. With the extra speed, there is a LOT more kinetic energy those brakes have to deal with. More energy, more heat.

How / when are you measuring the rotor temps? infared pyrometer after you get back to the pits is only a vague indicator. There are some temperature paints/stickers that will tell you in-use temps. Make sure the pads are up to the task of the heat the system is putting out.


Grooved rotors = aggressive pad compounds chewing up hot rotors. Possibly combined with the backing plate / rivets holding the brake compound onto the backing plate (if that is the style being used by those brake manufacturers) that are contacting the rotor as you wear the pads all the way down. Some pad compounds are worse than others for rotor wear.

It does sound like you still have some air trapped in the system somewhere, ABS unit is a good bet. Although I can't help you out with how to activate the ABS pump while bleeding. (Hopefully someone here does, cuz I'd like to know!).

You could also be getting some pad-knock-back, which can occur if running over rumble strips, long sweepers, quick transitions and off-track shenanigans. This can become more apparent as the pads wear down.

Ducting is definitely the more attractive option. Are you running the bimmerworld setup?

How? I was using an infrared pyrometer but I guess thats not the most effective way to check temps. Where did you source such paint/stickers? I know the paint is $$$ though.

Yep, definitely agree with the regarding the grooving. I figured the pad was eating up the rotor because the juddering was INSANE. That was with the Wilwood compound H pad at Lightning.

Hope someone on the board knows cause it would be pretty darn useful.

Never heard of pad-knock-back though... is this something one would feel?

[seatown88]

Heat is the issue that is going on. The Front rotors and pads are being overheated. Like NigelStu, put some temperature indicating paint on the rotors to collect better data. I bet you are reaching temperatures in excess of 1300F judging by your picture. You want to be around 900F typically, pad dependent. The best deal on the paint I found is http://www.raceshopper.com/temperature_paint.shtml.

[JRKOUPE]

...btw.....what is thickness of an e30 M3 frt pad?...

[dude8383]

Heat is the issue that is going on. The Front rotors and pads are being overheated. Like NigelStu, put some temperature indicating paint on the rotors to collect better data. I bet you are reaching temperatures in excess of 1300F judging by your picture. You want to be around 900F typically, pad dependent. The best deal on the paint I found is http://www.raceshopper.com/temperature_paint.shtml.

Very cool, thanks for that link! I've shopped with those guys before, didn't occur to me that they had it.

...btw.....what is thickness of an e30 M3 frt pad?...

Probably around 18mm?

[NigelStu]

Best part about the link seatown posted is the list of pads for temp ranges! nice to see that all in 1 spot.

I've used this stuff in the past. I like that it can show a range, instead of just chaning color once a temp is reached.
https://www.pegasusautoracing.com/pr...asp?RecID=4974



I'm running ChumpCar, so no fancy bimmerworld backing plates. just ducting. I'll have to build up a set of my own. Will need it for next year since the car will likely go from M20 to M50 power :)


You wont feel knock-back happening, but you will notice it when you apply the brakes - it feels a lot like a bit of air at the caliper, press the pedal and it goes almost to the floor, next application and brakes are there. Hitting rumble strips / curbing can move/shake enough stuff around to push the pad/piston back into the caliper a bit. First press on the brake pedal simply pushes the pad out until it contacts the rotor, next press solid brake. The difference compared to boiled fluid is the air is between the pad and rotor instead of inside a caliper or brake line. Had this happen on a 350Z with Brembos and all the time on my Spec Miata. Caliper flex, vibration and loose/worn hubs can cause knock-back.

[dude8383]

Best part about the link seatown posted is the list of pads for temp ranges! nice to see that all in 1 spot.

I've used this stuff in the past. I like that it can show a range, instead of just chaning color once a temp is reached.
https://www.pegasusautoracing.com/pr...asp?RecID=4974



I'm running ChumpCar, so no fancy bimmerworld backing plates. just ducting. I'll have to build up a set of my own. Will need it for next year since the car will likely go from M20 to M50 power :)


You wont feel knock-back happening, but you will notice it when you apply the brakes - it feels a lot like a bit of air at the caliper, press the pedal and it goes almost to the floor, next application and brakes are there. Hitting rumble strips / curbing can move/shake enough stuff around to push the pad/piston back into the caliper a bit. First press on the brake pedal simply pushes the pad out until it contacts the rotor, next press solid brake. The difference compared to boiled fluid is the air is between the pad and rotor instead of inside a caliper or brake line. Had this happen on a 350Z with Brembos and all the time on my Spec Miata. Caliper flex, vibration and loose/worn hubs can cause knock-back.

O_O $74 for an ounce! Where do you apply this stuff? Directly on the caliper or the backing plate of the pad?

LOL, gotcha. Did you at any point run the car without ducting?

Thanks for breaking down the knock back deal. So as I was reading your description I thought that might have been what I was experiencing BUT... this would only happen after about 15-20min of lapping. Wouldn't something like this become more apparent in a shorter period of time?

I honestly think that the bloody pump has air caught in it because the pedal feel would diminish after engaging it.

*edit*

http://www.e36m3blog.com/brakes/

Reading here he talks about the pedal dropping to the floor after 20 laps... I'm beginning to believe that my brakes are just cooking EVERYTHING and in turn diminishing pad life and boiling the fluid.

[NigelStu]

Edge of the rotor and edge/back of the brake pad backing plate.


Yeah, we ran without ducting first couple of races. Never had pad or fluid fade (Cobalt friction pads / ATE or the new Prospeed RS683 fluid), but we were also driving the car keeping in mind we needed to run a whole 7 hours, so not as hard on the brakes. Just more wear/heat than I like to see - you know shit is getting hot when wheel weights fall off when the car is sitting in the pits! (forgot to add tape to a wheel...)


Yeah, knock-back can/will happen first corner, not time dependent.


It sounds like you've narrowed it down correctly that there is too much heat in the system for how you are using the car. Small/thin pads, no cooling, higher speeds than stock and greater braking needs = too much heat. Add some cooling, maybe step up to a higher heat-tolerant pad. If still having issues, up-size the pad.