We have a 5 series BMW built for chump car. It's gutted and prepared so I don't think we can remove anymore weight. We have a chronic rotor warping issue.

1. Have tried different rotors
2. Running ducts (2 hoses per wheel toward the hat, no dust shield fabrication )
3. Current pads are cargo tech xp10 but occurs with others as well, as expected. Yes they get bedded in.
4. We run a cool down lap before pitting.
5. We tried turning rotors before they got too bad then using them but same effect.

Looking for suggestions. I had an m3 that was the same. Ducts kept the pedal taller but it warped rotors. The only bigger brakes from BMW are for the 850 and it would mean 600 bucks plus 17inch wheels. Not interested in that. Beyond 5-7 hours we end up braking at high speed then have to drift the car in to scrub speed into the corner. Fun but shitty on the tires. At the slower speeds the braking is violent.

 

You have clearly verified that your warping the rotors with a dial indicator? You have ruled out uneven pad deposits?

The carbotech's are known for being very sensitive to bedding procedures and since this is a chump car that will run lap after lap after lap I would recommend trying another pad as well like a Cobalt XR1/XR2 or Hawk DTC 70/60.

As for warping, we found that 9 out 10 warped rotors were warped....in the paddock.

When I come off track and get out of the car I go back to in 1-5 minutes and roll it forward, then come back and just roll it back so the hot pad heat-soaks a different part of the rotor. Haven't dealt with a warped rotor since but I have dealt with uneven pad deposits that caused the car to shake the steering wheel out of my hands.

 

I certainly will try other pads. I bedded these the same way I bed them on my s2000 with same xp10, and I have not had transfer of pad material issues. I don't know what dial indicators are...I am the least capable wrencher on the team but will look into it. We did 720 laps during the race. The car went out fine. The longest pit before the issue started (again) was 5 minutes for fuel. Rocking the car during pit is not really an option. Again we are doing a 2 mile-ish cool down lap.

Short of those fans they have in F1 for the radiators I have run out of ideas. I would think rules won't allow any electrical device present during fueling anyway.

 

Dial Indicator:
http://www.youtube.com/watch?v=H_1ySs7liS4

Like I said... sensitive to bedding. What bedding works on the S2k may not work on the Bimmer. IMHO, as someone who's raced and crewed in enduros I will say, I wouldn't run XP10's in that type of event. I consider them HPDE pads only, but that's just my opinion.

Is your brake pedal pulsing during braking? If you answer NO there's a good chance your problem isn't warpage.
Is your steering wheel, under braking, rotating left/right/left quickly or just "shaking"? If you answered Just Shaking, then it's probably transfer layer.

As for rolling the car back and forth... I'm not recommending doing that during a pit stop, I'm talking PADDOCK. After you come off track and park the car then after a minute or so, roll the car only a little so the pad is just resting on a different part of the rotor. No rocket surgery involved.

 

x2
don't let the car sit, cool down laps sometimes are not enough.

 

moving the car a foot or two for at least the first ten mins after leaving the track always helps disopate the heat.
Never ran into your issue there though.
I did find over heated brake pads once though.
I thought the lack of braking power after a session was a warped rotor but upon close inspection of the pad i found cracking in the pad material ,and it crumbles.
That was with the hawk blues up front. I did use HT10's, for a spell, and they are a nice agressive pad and I never had any issue with .
Now its carbotech in my front, and you do have to bed them in slowly but thoroughly.

 

I think trying more pads is the only option. This car is strictly endurance racer, if it's not a 5 min fueling stop, it's tire change or rotor change. I don't know of the car ever coming to pits with rotors feeling bad AFTER pitting. They always seem to progressively go down hill WHILE driving the 2 hour stint.

 

It only sits when fueling (5 min) Even when the race is red flagged we keep it rolling a bit back and forth. I am starting to think its just a fact of this make and model.

The very same way so many s2000 owners have chronic rotor cracking. Cit doesn't mater what outside temps are, cooling ducks or not, dust shields or not, or rotor brand. They just break after a few days of track use.

 

There is a really good article on this topic here by stoptech:

http://www.stoptech.com/technical-su...nd-other-myths

Based off this, there could be other problems causing it.

 

Whats puzzling is 2 of the 4 drivers use xp10 with no ills on our track cars. But maybe with the chumpcar we have too many cooks in the kitchen. The article certainly explains why after turning the rotor at road Atlanta the violent pulsing came back soon after.

 

Last year when was faced with cracked rotors, vibration, TV and other braking problems I did extensive research which ironically led me down the road of "air-bedding" my pads (which you can't do on a RWD, sorry folks). My transfer layer is exactly what this article mentions, Blue or a grey/black, depending on my chosen compound, in which I used 5 different compounds last year.

Some pads are going to be more sensitive regarding laying down an even transfer layer while others much less. If you spend enough time with the search feature you'll see that many people have determined that Carbotech's are one of more sensitive pads regarding bedding and even transfer layers.

And this is a very profound statement regarding race pads and bedding:

 

I think we will try cobalts. The car owner is talking about porterfield r4-e. any advice on those?

 

Try them all! Ok ok, all joking aside... In the bigger picture, brake pads are cheap and they area wear items. Like I said, last year I used 4 different compounds.

Last year I ran:

• Cobalt XR1 and XR2 (both of which wear at the same rate on my car).
• Raybestos ST43: Caused all kinds of vibration and I had transfer layer problems along with brake heat problems. (These pads withstand SO MUCH heat that everything else in your braking system will fail before these pads do FYI.)
• Performance Friction Compound 83: Brilliant pad but would cause my rotors to crack prematurely. I couldn't figure it out but when the rotors didn't crack the pads were brilliant. Old compound and I don't think it's in production any more. If you can find the PFC 90 or 01 you should try those.
• Hawk DTC 60 (the 70's aren't available for the CRX): This was my new favorite to replace Cobalt because they were affordable and worked very well. No transfer layer issues and handled heat well.. However don't over heat them this WILL result in the pad material delaminating/detaching from the backing plate.

The Raybestos ST43 is a good pad and wears like iron and the majority of the Bimmer guys here refer to them as the "miracle" pad. Great enduro pad. I haven't been able to make them successful on the 9.5" rotors of my ITA CRX. For this season I am going with the less aggressive ST42 compound from Raybestos.

The Cobalt XR2/XR1 are great pads, I used them with great success and never suffered an uneven transfer layer. The only reason I stopped running them was due to fulfillment problems regarding the order. It took me 12 weeks to get the pads. If you have large-ish rotors (10.5" or bigger), they should last and last well. My competitor in an Integra (which has larger rotors than the CRX) ran 1 set of XR1's for half the damn season! I almost sold the CRX when he told me that.

I was able find an outfit that stocks the Performance Friction Compound 80 (very old but reliable compound) and it's less aggressive than the 83 so I'm going to try that. It is my understanding that the 83 is a rather brutal pad.

As for the Porterfield R4e, I heard mixed reviews. BUT, for a Lemons car it's definitely worth a shot and we'd all be interested on your review of this pad. Bedding, wear, heat, stoppping etc.

 

play in the suspension/steering promotes uneven pad wear too.

check balljoints and steering rack for play.

 

Much thanks Rice Classic. Appreciate your time.

Thanks Tyson, worth a look, its an old tired car that has 7 endurance race weekends on it. I sure don't want to do a Montoya at Daytona in May.