JEPopp

So, at Autobahn last weekend with NASA. 1st session, 7th lap, ABS fails going into turn 8, seriously flat spoting the front tires. Thankfully, I did not go off track or hit any other cars. I check connectors etc between sessions, but nothing obvious.

2nd session, ABS failure again after only 3 laps. I cut the weekend short to avoid flat spotting the tires to the point where I can't drive the 70 miles home, or heaven forbid a more serious accident.

The dealership diagnosed a bad wheel speed sensor on the left front. Has anyone else had a similar issue?

Car is a 2012 Grand Sport, DBA 4000 rotors, stock calipers, Carbotech XP12/10 pads. How hard am I on brakes?... I'll go through front pads in ~2.5 track weekends. I installed brake ducts this year after boiling the brake fluid (Motul 600) last year at Gingerman.

I've never had any serious offs, or hit potholes/curbs on the street, and this is only the 6th track weekend in the car. At this point, I'm assuming the failure is quite possibly heat related. I know the front rotors reached 1100F because the temperature sensitive paint markings are all white.

Thanks!

0Anthony @ LGMotorsports

See what is causing the failure......

You can upgrade the front hubs to the ZR1 units (made by SKF) if you are seeing play in the bearing..... The failure could be the bearing coming loose causing it to loose contact with the sensor, or possibly a wire got crimped/cut/burnt so you should go through and check all of that. Personally I would say you need to do this, unless you know a good tech at your dealership that knows more than codes on the Tech II.

With that being said, race pads on stock brakes and a wheel speed sensor failure will be a big mess so I have no doubt you were locking up tires and it probably felt a little funny under hard braking as well before they locked up as some of the dynamic prop. is getting screwed with too.

1100F is up there...but not to extreme under track conditions.

JEPopp

Thanks for the response, Anthony.

The hubs appear to be ok (no movement), and I'll make sure to double check any visible wiring. I trust the tech at the dealership completely, he's one of the best in the Chicago area.

RX-Ben

Did you check the DIC for codes?

StKnoWhere

What lights on the dash and messages on the DIC?

Did you over brake or did the car lock up the brakes unexpectedly?

Wheel sensor related is Fairly common on C5 and C6., dozens of threads and hundreds (thousands) of posts. Following is one one of the more helpful.

https://www.corvetteforum.com/forums...need-help.html

Wheel sensor related will generate "Service Active Handling/ABS/TCS" messages and the ABS and TCS lights will be on. Cause can be: connectors, harness, hubs or ECBM.

Unintended activation of brakes can be the steering wheel sensor. Disconnecting it is a work around.

https://www.corvetteforum.com/forums...-defeated.html

Pulling the codes is the first step.

Let us know the outcome but I think some SKF hubs are in you future either way.

whatcop?

So when you flushed the brakes how did you do it? Did you fully clear the lines then add the new fluid? If so did you have a tech 2 put on the car and actuate the ABS system to clear it?

JEPopp

DIC codes - good question, I failed to mention in my initial email: Yes, the DIC was showing "Service Active Handling/ABS/TCS" messages and the ABS and TCS lights were on. After shutting the car off, and re-starting the codes disappeared - until the 3rd laps of the 2nd session.

The front wheel lockup happened as soon as I hit the brakes (or so it seemed), then released after pumping the brake pedal a couple times.

StKnoWhere - Great link for a previous thread, thanks! Knowledge is good!

whatcop? - Brakes flushed prior to the event using a Motive power bleeder. I pushed nearly 2 bottles of Motul 600 through the system.

As soon as I know the codes, I'll post in this thread.

dfinke23

Same problem in 09. While looking at the WSS connection I found a hogged out pin port so it was losing connection intermittently. Happened again on the other side a few months later.
I switched to the ZR1 bearings and checked everything during the switch and have not had a problem since.

RX-Ben

My guess is that about 95% of ABS problems are due to the wheel speed sensor plugs or damaged wiring coming from the hub.

JerryTX

I do not know C5's but this is exactly how the C6 behaves when it has a bad/intermittent wheel speed sensor, replace the hub and be done with it. I chased this with ABS module replacement and I can't remember how many other things we tried. End of the day after enough flat spotted tires it was the abs sensor going bad. Mine would lock the passenger front every time, meanwhile it was the drivers rear that was bad per the error code. I suspect it went bad when the axle stub shaft snapped at that same location.

StKnoWhere

All 3 codes and both lights is likely something in the wheel sensor circuit. It clears when powered down and can some time to register upon restart.

Removing the ABS fuse or Pressing the traction control button until everything is off (I think...) is a workaround to prevent a surprise on track.

JerryTX

Yes that is a workaround but the static brake proportioning is horrible so it likely will feel like crap and lock up the fronts way too early and easily. Turning off TC does not disable ABS in a C6 at least, that would have no impact here.

Bill Dearborn

Actually, if the ABS isn't working you loose the dynamic rear proportioning capability of the ABS system so there is more of a tendency to lock the rear wheels under hard braking.

Bill

StKnoWhere

If both lights come on, TC is disabled. The point was you can turn it off before the speed sensor triggers to prevent a surprise on track.

I still haven't found my problem after cleaning connectors, replacing cables and hub. Got the "ding, ding, ding " and the lights and Service messages came on today not moving and stuck in traffic. Very frustrating...

RX-Ben

You need to follow the codes and replace everything at the applicable corner if the issue continues, the bearing and all connectors (don't just clean them, install new ones). The most common problem with the connectors isn't that they get dirty, it is that the female pins spread and the connection is intermittently lost.

StKnoWhere

Understood, everything from the hub to the connector on the subframe is new. I even cut out the subframe connector and solder spliced it to the speed sensor harness.

RX-Ben

Which wheel? The inboard wires can get damaged if unprotected from heat.

JEPopp

Hey guys - good comments.

I spoke with the Tech today when I picked up the car. I did not get the exact codes, but they indicated a bad wheel speed sensor on the left front. When the Tech looked closer to try and understand why, he found some wear on the insulation exposing a very small amount of wiring. Rx-Ben - looks like your hypothesis above remains true.

A new left front bearing was installed (seems the 2012 Grand Sport uses the same bearings as the ZR1). Now, I need to find some open road to put some heat in the brakes and see if the problem reappears. Let's hope not, because I just put new Bridgestone RE-11's on as a result of the flat spotting.

Thanks - Drive fast & stay safe!

John

StKnoWhere

LF, it can take five miles of driving before it triggers.

StKnoWhere

Glad they could help and thanks for posting the outcome.