tytek

So... I was at Putnam today and was running a new-at-the-track-to-me C5Z that I bought off of a forum member a few months ago. I was only 4-5 laps into the day, and the car was warming up nicely, and I was starting to get used to it. With LG coilovers and various other mods, it behaves differently than my street C5Z that I used to track.

I had TCS No Comm issues with this car right after I bought it... but thought that I had fixed them, as I have not had any problems running two autox events and doing limited street driving. Until today, that is. I had the error codes come on when I was getting the car off the trailer, but after clearing them, they have not come back. So, I decided to track it anyways.

A few laps into it, the car spins at the end of the main straight, as I was hard on the brakes slowing down from 133mph. It looks like one or both of the rear tires locked up and initiated the spin. It also looks like the engine died immediately after the rear end started to slide out from under me (can be seen on slow motion footage). Is that normal?

What I found weird was that the car was braking fine and slowing down OK, until the *** started coming around. Happened super fast and I became a passenger, looking out in the direction of travel - seemingly interested in what we will hit as the car continues to rotate.

Any idea what could have happened? Lost ABS and with weight transfer locked up the rears and spun? Mechanical issue where diff or tranny locked up? I ended up being lucky not to go off to the left, as the guardrail is relatively close to the track there.

This is the regular speed video:


Slow-mo video:

Olitho

ABS Failure. Check all the wires to the hubs, the connectors, etc.

Then check voltage on the hub ABS sensors.

Then check and make sure the ABS module is good.

Also make sure no hard lines or flexible brake lines have been pinched.


I have done what you did a dozen times on unexpected ABS failures.

tytek

Weight transferred to the front, rears got unloaded and locked up due to ABS failure?

I have checked all the connections, must the a bad EBCS. I have a spare that is good. Will swap and see what happens.

Seems like a dangerous freaking issue. I could have just as easily spun the other way and hit the armco. Not sure how I feel about this Corvette ABS failure...

Olitho

I find my system fails with some regularity for one reason or another. If you drive like it is not an ABS system, but let it just kick in a bit on bumps, when a wheel gets light on a declining radius, etc. it is not so bad when it fails unexpectedly. If, like most people on track, the driver hits the pedal hard and/or mashes it will take you for a ride when it fails.

You were starting to initiate a turn while braking (I will retract that comment, it does not appear you initiated any turn at all), and this is normally fine, but that is why it appears you went for the sudden ride. I am failure certain your brake application was probably fairly sudden on top of aggressive. It is a disconcerting problem for sure, but I have adapted my driving.

Sure weight transfers, but the biggest issue is abrupt and aggressive brake application coupled with the fact that the electronically controlled bias is gone with ABS failure and these cars often seem to default to an incredible amount of rear bias. Are you on stock brake calipers and rotors?

mgarfias

What Oli said. I've been fighting that nocomm thing for 5 years now. Thought I had it fixed, but it comes back. I've had some luck pulling the EBCM connector and spraying inside with contact cleaner. I have the feeling that when I lay down the radiator I should get in there and remove/replace the whole connector.

Olitho

One of my fixes required replacing the whole main wiring harness. It seems like after five years of tracking the harness can become a suspect component in the ABS system. I have seen this change required in other cars to get it working right again.

mgarfias

Do I even want to ask what that cost?

Olitho

I don't remember, and when that happens it is because it was a lot of money. $1200 as I recall....

flink

Those rear biased brakes are a ticking bomb on a track. It should be easy enough to fix - get them front biased with a single channel proportioning valve between the rear master and the ABS. Pull the ABS fuse then get the valve set so the fronts lock first.

tytek

I am on stock calipers and running Wilwood H pads. Rotors are DBA5000.

Since I was trying to brake deeper into that corner, I was probably too brutal in my brake application. The suggestion to drive like there is no ABS is obviously a very good one, and I'll take this spin as a learning opportunity to be smoother and to fine tune my threshold braking, as well as pedal application.

tytek

A buddy of mine made the same suggestion. As expensive and time consuming as this can be, it probably will save me money in the long run. Stuffing a car into a wall, or having to sit out a weekend ain't cheap either.

Does it require gutting the car, in order to replace the harness?

I will also give some thought to eliminating ABS and mechanically setting brake bias with a valve. I like the safety net of a working ABS system, as I am not that good of a driver, but when it fails unexpectedly, I can't trust it.

tytek

Here is what my off track escapade looked like on Harry's Lap Timer. It happened at the end of the main straight, just before turn 1.

tytek

And a few more relevant graphs:

andy3101

I have experienced this as well. Took all the abs out of the car and run manual prop valve in the rears. I will say having abs is definitely an advantage but having a consistent car is much safer....

One of the most dangerous situations on track is when you have no idea what your inputs might do to the car.

Just be glad you didn't hit the guard rails or even worse another car.

Apocolipse

I am in the same boat as above, no abs.

Han Solo

WOW, that is scary. I guess this is another reason I never tracked my C5Z.

I am surprised it stopped as quickly as it did. You are very lucky you didn't have contact with anything.

I've only had one off in my years of tracking a 99 Mustang and I went much further and came to rest in a chain link fence and bushes from a much slower speed off. (turn 9 at RRR from about 90-100)

I pulled the ABS fuse one time and flat spotted a new tire within 5 minutes. I am sure I could get used to not having ABS if I tried but mine works perfect and allows me to slam the brakes as hard and deep as my nuts will allow so there was no reason. I guess I'm about to learn cause I am moving to a tube frame car with no such fanciness.

Hope you guys get these problems worked out!

t.renz791

Read all posts in this thread... if this happened while trail braking it would be a disaster.

Yikes.

Olitho

There is no reason to be afraid of trail braking. Interestingly enough this ABS failure is usually easier to deal with when trail braking as that is not a threshold braking situation and usually just the lighter wheels start to lock and/or the car may start to slide, but lifting the brake timely typically allows for recovery. It is the threshold braking when full ABS is expected that his problem will bite the worst.

I seem to know too much about this....

Racingswh

Wow. So lucky there wasn't anything hard to hit. I am not sure I could live with that. You guys that do I don't know really how you're willing to accept that as normal. I would be fast after a solution or selling the car. Best of luck and glad you're ok.

SouthernSon

Have tracked my C5Z for several years at Putnam, usually 6 trips a year, with only one event causing a problem. Flatted spotted a couple of tires when ABS module died. That was about 4 years ago. I sent it to ABS fixer and it has been great ever since. I can't bring up your video for some reason but I go deep into T1 after a 140ish mph straight with no problem. Hope you get it resolved without too much pain.