TKOGTO

Anyone experience this on track?

Felt car dart to the left about 2 to 2 1/2 feet under hard braking from above 100mph. Confirmed it in review of video. The higher the speed the greater the move.

If experienced, what was the cause?

Thanks

troyguitar

Seized piston/caliper, probably at RF corner is my guess. Pull RF wheel, open bleed screw and see if you can fully retract all of the pistons (can usually just use a screwdriver as a pry bar) and slide the caliper freely if it's on sliders.

With multiple pistons, a single stuck piston in one caliper might not be noticeable except under hard braking. Air in the lines could also make weird things happen. I'd bleed the system in addition to checking the calipers.

ScaryFast

In this case I would check your front hubs. Most likely one or both wheel bearings are bad. I've had the same thing happen;
Checked calipers: fine.
Checked DTC's: nothing.
Checked history DTC's and found intermittent faults from both front ABS sensors. If the hub is bad, the teeth in the tone ring can literally crash into the sensor itself. Looks like lockup to the system, and ABS steers you into the grass.

Most tracks are right turn dominant, which is why front right hub wears out fastest.

0Anthony @ LGMotorsports

I agree with the two above statements.

Couple other things to look at
Camber/Caster
Toe

Also...and I know it probably goes without saying but a damaged or broken suspension part. Bushing, tie rod, ball joint.....any one of those things broken or left loose can do odd things under braking if the car starts to toe out on one corner causing the car to dart.

CONE RACER

I've had three similar instances. Root causes each time were: caster jacked way out on one side, stuck caliper, and bad rear toe link (tie rod end).

fatbillybob

You Only pull at one braking zone over 100mph or are there many different locations this happens? Sometimes you can be very surprised at what you see walking a track that you can't see or feel from inside the car. You learn things about a track and sometimes learn why your car does what it does when you drive there. Add that to driving style or in this case braking style and you can get what you get. What happens if you move the braking zone?

TKOGTO

Interesting because caster was way out on left side (~5/32nds) prior to this issue showing up. The car was aligned to fix it as I had a pull to the left just trying to drive straight. Shop is checking alignment, suspension components as I write.

It showed up significantly @ the end of the main straight @ ~135mph. In the shorter straight @ about 107mph it was also present but a fair amount less. Driver coach got more here but broke ~ 20ft later @ 2-3 mph more.

Track is not new to me. Been there 20+ times. Also viewed vids from Oct 2014, no similar dive to the left. Brake style in shorter straight was unchanged but brake point and style changed a fair amount in main straight (later and less initial application this day).

I have to review the vids more carefully to see if changes in my brake point throughout the day, later little by little, affected the issue.

TKOGTO

It better not be the bearings. Put new SKFs in July 2013, about 13 track days ago.

I will check the DTC history re: the ABS sensors. Once each of the last 4 track days, the brakes sort of failed in the brake zone of the main straight (3 different tracks). It only happened 1x each day with zero warning and brakes were fine thereafter. My guess is the ABS sensors gets messed up with different friction levels between Wilwood H pads and MPSS tires and senses a lockup. No pulsating though.

blueekb

This happened to me once right after getting car aligned. Turned out shop didn't tighten front left lower control arm bolts enough. Everytime I slammed on brakes it moved.

Cost me a track day but at least I figured it out that night and was able to finish out the weekend.

bb69

I would also check the rear lower control arm eccentric bolts. If those are loose, the car will do all sorts of fun stuff as you transition from power to brakes.

Ken

TKOGTO

Car was aligned just before the issue popped up so maybe. Anyway, shop reported "some" play in the tie rod on the passenger side and a fair amount in both of the inner UCA bushings. Having them replaced. Will be tested next week.

Z06TWT

I had a similar problem at the end of the long straight at Road Atlanta.....after I had the ride height , alignment and corner balance done correctly it cured the issue.

SouthernSon

You might check the 'dog-bones' on the A-arms and make sure they are cinched up tight since the alignment as well as the other things mentioned. Any individual component of the suspension - springs (my front cracked and gave way on both ends last year), shocks, brakes, pads, etc.. can cause it to some degree.