I took another track day this weekend and was having major major issues with locking up my brakes -- consistently on the driver-side front. So much so that I wasn't enjoying being on the track. I even corded one tire (see pic, but never mind the poor wear pattern... bad alignment). I kept running on my street tires -- still locking. I flushed the brake fluid -- better, but still locking. I think I generated smoke at every single braking zone at one point or another.

I don't think I was driving any differently -- but it's possible I was just braking sloppily. It's my 944 with 968 motor, which has no ABS, Willwood brakes up front with racing pads, and stock rear with just metalmasters.

Aside from learning to brake smoother -- is there anything that can be done mechanically to help alleviate this problem? Better pads in rear? Different fluid? Less camber?

I'd appreciate any input -- especially since I'm wasting expensive rubber with my poor braking....

 

Lots of things impact brake lock up.

Track is one of them.

Also brake pads and how much they are worn down. Alignment and also worn shocks.

 

Looks like you created a flat spot, and once that happens it will keep locking up at the same spot, and just get worse and worse. Was your braking in a straight line or was that tire unloaded in the brake zone?

____________________________________
1986 944 NA - Guards Red - 91k miles
1983 944 NA - Platinum metallic - 1200 mi beginning a new life
1985.1 944 NA - Guards Red - donor car
1984 911 Carrera Coupe - Guards Red (gone, but not forgotten)
"If you're not living on the edge, you're not living"

 

I would think these two different kinds of brake pads could upset the front-rear braking balance, but that's just a guess.

 

Thanks guys. Keep the ideas coming, that'll help me figure it out.

One strange part was I was always locking up the front-left. And not the front-right. People watching noticed that as well. My first reaction was air in the brake line (front-left is the shortest line) -- but flushing didn't solve it.

That particular braking zone was on an uphill (followed by a turn after the crest on the other side) -- so my wheels did get light and lock up on the crest.

 

If the problem is only occuring at one corner on one track I would attribute the issue to the track. There are all kinds of reasons why you can lock up a tire or both a certain points on the track. If you DE the best plan is just to drive around the problem. If you race it depends on how much time it costs as you may need to adjust the car.

At PIR the braking zone for turn 9 (hairpin) is bumpy. Get on the brake really hard in just the wrong spot on the you will lock the brakes on one of the little bumps. My solution is modulate the brakes at the is bump. I basicly get on the brakes hard, let off a little and get back on it hard when I feel the front end settle. Not idea, but works. I have replaced the shocks in my race car, but have not had chance to check how this impacts braking in that spot. Maybe it will solve the issue. Maybe not.

 

What's weird is that it's now happening all over the place.

This weekend I was doing DE at Buttonwillow (counter-clock wise). I've done this direction three times before. In the past, I used to lock them up coming into Turn 4 (the little dip down on the far corner) -- and learned to drive around that by braking early before getting to the dip, let off a little, and brake some more once the car settles. But this weekend, I locked up on turn 3a (where I flat-spotted), turn 13 (end of the main straight), the end of esses going into turn 11 (we didn't do mazda-star), and turn 6 (end of NASCAR). So I was like, WTF?

Track days are definitely not as enjoyable when you're worried about braking everywhere like that.... I want to try changing a couple of things before next weekend...

 

Any in-car video? Interesting problem, hope you figure this one out- if just for the sake of that poor little tire!

 

Sounds like what is happening to me in my 951.
Always the front-left brake that locks up. Doesn't matter if I'm turning left or right.

*watching this thread now*

 

Has the car been corner balanced? If the cross weights are way off, that could cause the lighter corner to lock up.

Does the front end feel squirmy under heavy braking?

I would use racing pads on the rear to utilize more of the rear braking potential.

 

No video. It's a car that's slowly but surely going down the downward spiral of track car. So more toys to buy....

And has not been corner balanced and I haven't noticed squirminess -- though I have been neglecting the rear brakes. That's one more item to put on the shopping list.

One thing I remembered just now is that the passenger side rubber bushings on the control arms and castor block are worn out more than the driver side -- that could explain why my driver side locks up more.

 

sometimes a brake line can become collapsed, to the point that when you press it, and depress it, it wont let fluid back out of the caliper, causing it to stay on. Im not saying thats the problem but you may want to check it out. If you can drive awhile and it goes straight, you hit the brakes and it brakes straight, but when you let off it starts to pull- its the lines. If you brake and it starts pulling, its the caliper- and if its just locking because there is too much brake then....

 

I didnt read all the responses thoroughly, so I apoligize if I reiterate something that was already said:

What was the condition of the tires? Old dried out hockey puck tires will be very easy to lock up.

Fluid bleed: did you do both fronts or just the side that was locking up? I would be more concerned about bleeding the side that was not locking up - The side that is locking is getting plenty of pressure (too much), the side that is not locking is possibly getting less pressure (could be air in the line).

I would also run the same or a higher torque compound pad in the rear, than the front. Since you added larger calipers in front and are running a track compound in front, but street compound on the stock rears, you have really thrown your brake bias off, so not too surprising that youre locking the front up.

Otherwise, as other mentioned, could be an alignment problem, bad shock, really far off corner balance, or you are slowing down too much right before turn-in (brake pedal modulation/technique).

Check/fix some of the easy and cheap things before going back to the track. If the problem continues, have an instructor ride with you or drive the car to determine if its a car setup problem.

 

If you have significant camber differential between the sides under braking, either static or dynamic, one side will have less grip. If the coefficient of friction of the rotor/pad surface exceeds the road/tire surface on the side with more camber and inversely on the opposite side, it could lock one side.

If you haven't changed your setup since I drove it, the soft suspension and resultant change in camber under loading might be contributing. Maybe time for stiffer springs and sways?

 

Everything I have read advises against using such bias in pads front to rear. You are basically forcing the front tires to absorb nearly all of the energy.

Also, as mentioned above, once you flat spot, the tire will continue to lock up at that point if you keep applying the same brake pressure as before you flat spotted.