...and as I brushed the brakes prior to entering the Kink, I thought the brake pedal felt a little soft. As I'd normally be braking from ~130 mph at Canada Corner, I thought that maybe now would be a good time to back off a bit.
Started braking way early, and the pedal went all the way to the floor. As I continued pumping the brakes, I could hear the ABS working and then the car (BMW i8) threw a regenerative braking warning at me. In the end, I made the (pretty sure correct) choice to just take the car straight into the gravel trap. Was probably going about 20 mph entering the gravel. Car came to a stop with no damage.
Brought the car back around on to the track, though it wasn't moving as fast as the corner workers would have liked and made my way to the pits. Stopped (poorly) at the hot grid for a review with the event master and they saw that there was a lot of brake fluid at the right front wheel. Carefully made my way back to the paddock, where I found the outer bleed nipple on the caliper completely loose-- like a turn and a half or more.
No one to blame for the mechanical state of the brakes other than myself-- I'd pressure bled the brakes before the event. This was the fourth event of the day, but the first at speed due to weather and the lead/follow exercises done in lieu of in car instruction, so it was the first time the brakes had gotten good and hot. As it was, I was probably 5-6 laps into the session.
Got a wrench on the bleeder to close it and a paddock mate provided brake fluid to refill the master cylinder reservoir, which did not appear to be completely empty. At that point, the pedal was firm enough to provide normal operation for the drive home-- with nothing at stake other than the loss of a day at the track, I decided not to go out until I can pressure bleed the brake system again.
Successfully home now, car is up on the lift and the trip into the gravel appears to at most done a little rubbing on one of the jacking pads.
All-in-all, I feel kind of lucky.
That could have ended substancially worse. Someone may have been looking out for you.
Don't buy any lottery tickets, you probably don't have any luck left.
that could have gone very sideways. Glad all you harmed was the jacking point and your pride.
Agreed that this could have gone much more pear-shaped than it did 
So, for a point of additional discussion, anybody ever heard of bleeders loosening up in hot calipers?
Just for the drill, and since the parts aren't all that expensive, I'll be replacing all of them when I bleed the system, then marking them with torque seal, so I can at least monitor the visible ones.
In reply to Karacticus :
I've never seen one come loose. One of the calipers on the G35 has a bleeder repair kit in it. I think I'll make sure I double check it before it goes back on track.
In reply to Karacticus :
My adventure at the Kink started when the Black Jack suddenly sped up on the cool off lap.I entered Canada corner at my usual speed of about 150-155 and leaned on the brakes without the usual assistance of the engine slowing down. In fact the engine was now at full throttle. The throttle was flat to the floor (a piece of track debris held it wide open). Luckily Even though it was built in 1958 it has superb brakes. But not enough to allow me fully bring my car under control. Empty track so I entered too fast. Fighting control I slightly overcooked it and slid off the track to the inside and tapped another car that had broke down earlier. My one and only accident in 5 decades of racing
There is a kink shaming joke in here somewhere
Karacticus said:
So, for a point of additional discussion, anybody ever heard of bleeders loosening up in hot calipers?
Just for the drill, and since the parts aren't all that expensive, I'll be replacing all of them when I bleed the system, then marking them with torque seal, so I can at least monitor the visible ones.
i've not dealt with them loosening on track, but i've dealt with them being just not quite tight enough to still leak.
i'm not saying that's what you did, just playing devils advocate since the BMW has regen braking.. i wonder if you just didn't work the brakes hard enough for it to be an issue till you were at RA.
but... with the speeds you were going.. i could totally believe they worked themselves loose with a bit of heat to help them.
In reply to spacecadet (Forum Supporter) :
Agree most likely scenario is I didn't get that one tight enough.
However, regen isn't a factor when the car is sitting static after you've bled the brakes and are simply pressing the pedal-- they are just your regular power assisted hydraulic brakes at that point.
Though the parking/emergency brake drives the rear pads electrically, so that would have been an option I could have used too, but there's no way to modulate those like there would be with a mechanical hand brake.
In reply to Karacticus :
Interesting question: will it apply the the "e-e-brake" at speed? Or is it strictly a parking brake?
Jay_W
SuperDork
10/18/20 11:21 p.m.
There's hearing "click" when you expected to hear "bang", and there's this right here. Both are bad, I reckon it depends on the situation as to which one's worse. Glad ya got it parked safely!
Lost power assist on the front straight at PBIR. Was standing on the pedal with both feet as hard as I could like it was a leg press machine set waaay beyond my strength. Slowed the car enough to only go two off and keep control through turn one. Limped around the track, discussion with marshals in hot pit, found the new vacuum hose for the power assist had kinked once it got hot during a session. Scary losing brakes!
An accident isn't the result of a single bad decision, but a series of bad decisions which create an unrecoverable situation
Yes, you might have put yourself in the situation by not tightening the bleeder down enough.
I like the idea of marking the bleeders after you re-bleed them again. It'll make checking them after checking lug torques before each session a snap.
However, I really like the risk decision process I hear being applied... and the fact that you're sharing it, and seeking to improve.
Please continue.
Pucker moments on track are what make memories.
I have seen bleeders loosen a handful of times. I normally toss a torque wrench in them when I'm done bleeding brakes for a car that's gonna see track time when done.
Glad this ended up being a learning experience and nothing else! Do you even use regen at the track? Can it be turned off completely?
NOT A TA said:
Lost power assist on the front straight at PBIR. Was standing on the pedal with both feet as hard as I could like it was a leg press machine set waaay beyond my strength. Slowed the car enough to only go two off and keep control through turn one. Limped around the track, discussion with marshals in hot pit, found the new vacuum hose for the power assist had kinked once it got hot during a session. Scary losing brakes!
Turn 1 at PBIR is a joke compared to the one Karacticus showed, its a paved chicane.
Now turn 9 on the other hand! Even my NA miata will pick up some speed by the end of that straight. On a gen 2 CTS-V you would see high 150s and there is nowhere to go there
Slippery (Forum Supporter) said:
Glad this ended up being a learning experience and nothing else! Do you even use regen at the track? Can it be turned off completely?
Regen cannot be turned off, but when you're hard into the brakes, it's essentially bypassed if I'm recalling the documentation correctly.
The regen/drivetrain warning I got more or less coincident with entering the gravel trap was also about the point the battery was exhausted, it then cleared almost immediately.
I can say that during the rainy and lead/follow sessions, I actually exited the track with more electric range than I started the session with.
Between the electric front axle torque and the AWD it provides, the car exits a corner like a scalded cat. It also makes really awesome noises during foot to the floor upshifts that may or may not be entirely synthesized.
Slippery (Forum Supporter) said:
NOT A TA said:
Lost power assist on the front straight at PBIR. Was standing on the pedal with both feet as hard as I could like it was a leg press machine set waaay beyond my strength. Slowed the car enough to only go two off and keep control through turn one. Limped around the track, discussion with marshals in hot pit, found the new vacuum hose for the power assist had kinked once it got hot during a session. Scary losing brakes!
Turn 1 at PBIR is a joke compared to the one Karacticus showed, its a paved chicane.
Now turn 9 on the other hand! Even my NA miata will pick up some speed by the end of that straight. On a gen 2 CTS-V you would see high 150s and there is nowhere to go there
For those of you unfamiliar with Road America, at Canada Corner you'd normally be braking at the end of a half mile piece of not quite straight track that you (at track day pace) entered at the better part of 100 mph exiting the Kink.
Some stuff from the training guides on the braking system-- there's also a lot more with diagrams, etc, but not terribly good for sharing via this forum.
And, from the parking brake section of the doc. If operated at speed, it looks like it's still dependent on hydraulics until the car stops rolling. It might be slightly more useful than just pumping the pedal, or it might just result in pumping all of the brake fluid overboard by the time you come to a stop.
Very likely the nipple wasn't tighten enough. Find out what the proper tongue setting is and use that.
You could go further; when I raced motor cycles safety wired them but I'm still going with the bleed nipple not being properly tightened. I always double check them before I put the wheels back on.
I get to run this track again on friday! Cant wait!
