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Datsun1973

Eliminating Judder on Road Courses

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Car is a 1985 BMW 635csi, it's big, heavy and especially nose heavy.  I race in SVRA, VSCDA etc so not hyper competitive but I took first in class last weekend even with a horrible brake judder.

 

Here is the current setup. 

Front Brakes: 13x1.4" Coleman Floating rotors with AP Racing CP5800-10SOL 6 Piston Calipers Wilwood Polymatrix A Compound Pads

Rear Brakes: 12.19x.81" Fixed 2 piece rotors with Wilwood Superlite 4 piston calipers and Wilwood Polymatrix H Compound Pads

Master Cylinders are AP Racing with a bias bar no booster 7:1 pedal ratio.

First of all the car STOPS and in a hurry.  I can brake from 150mph+ to 50-65 for sharp corners no problem.  The problem is the car shakes like crazy until I'm hard on the brakes and there doesn't seem to be a lot of wiggle between no judder and lockup.  It does not judder when the brakes are cold on the first lap.

 

I'm thinking of going to PFC 01 pads based on some of the feedback i've seen on the board.  Any other potential pad compounds I should look out for?  It's a Hawk 109 or Wilwood 88 pad shape.

 

Edit:  This is a full race car so i don't have to worry about road manners outside the track.

 

Thanks!

Brakes.png

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What do you mean by judder?  could it be the floating rotors chattering on the pins? uneven pad deposits causing grab/no grab as you're gently on the brakes?  bad shock or slop in a suspension/steering bushing somewhere causing a corner of the car to shake or bounce?

My first thought if all of the suspension is tight is to dump the Wilwood pads.  I was never happy with them when I tried them on my car due to uneven pad deposits and high rotor wear.

Hawk DTC series are a next step.  I run their DTC70 on my car with Wilwood superlites and they last multiple seasons/set, and I have negligible rotor wear.  PFC or Raybestos ST-4* are other options, depending on the temperature and friction levels you are looking for. 

How much power does that car have and what tires (and size) are you running on it?  if you're able to even get to 150MPH on tracks around here, you must have some good power to make it hustle that fast.  with that much power, I also assume you have decent tires to provide the mechanical grip necessary..  Those brakes are also huge- large enough for 600hp car with aero and slicks kind of huge.

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Often the lower control arm bushings wearing out can give a highway shimmy in steering wheel under accel and turning; but not braking hard.

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the suspension is tight. It’s all new spherical bearings.  Rotors were new this race. Car makes 425-450shp depending on the tune I run.  Tires are 245 R7 Hoosiers up front and 275 R7s out back. I agree the wilwood pads seem to be the culprit. I had street compound pads with some M5 calipers and it was okay but faded bad so hence the upgrade.  DtC70 or 60 are an option as are PFC 01.  I’m looking for a good friction level that stays fairly constant with temp rise that I can modulate. I flat spotted my front 2 tires going into turn 12 at Road America last weekend trying to modulate but the pads didn’t seem to want to release unless I was all the way off the pedal. 

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change the pads, scuff the rotors, and see what happens.  I was never very happy with the Wilwood pads.

The Hawk DTC60 and 70 pads have a pretty flat torque curve after about the second brake application for me.  others have said they take a lap or two to warm up, but I haven't noticed it myself.  that said, quite a few people hate hawk pads and prefer other brands.

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Yeah going to do this ASAP.  Just need to do a lot more stuff too but thanks for the advice.  Looking at PFC 01, Raybestos ST44 and Hawk 60/70.  

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Any update here?  Curious since i have these calipers on a new car.

Thanks

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We went to a complete PFC system on my TA2 car (from a complete Wilwood system)...constant cracking of rotors (same with Wilwood), I'd crack a set (as in CRACK) every race weekend...performance was not that great either. Ditched that whole systems and went with Alcon rotors (FINALLY no CRACKING!!) and calipers and Pagid pads (rears are custom water jetted to fit)....sweet jalapeño...a GREAT braking system...FINALLY!!

So - does that qualify me as disliking the pads? Kind of...I disliked the whole system. Granted - the TA2 is somewhat of an interesting dilemma...15" wheels in a car that stupid fast and you really, I mean REALLY, need good brakes...so the system is REALLY stressed...we have all sorts of cooling. So, a PFC may work well in other situations.

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