I was at a track day at Road America in my C5 Z06 and had something happen which I have never experienced before. I usually put the active handling system in "competitive mode" and am able to rotate the car a little without it interfering. Today, on hard left turns (especially Turn 5 and Turn 6), I was not able to put the power down exiting the corners without the Active Handling message coming on the dash and the engine throttling back and it appeared to be dragging a brake as well. Once I tracked out of those corners, everything went back to normal. On right hand corners, I could rotate the car and get on the power early. The only way I was able to not get the message in Turns 5 and 6 was to really take it easy and be very careful with the throttle. There was plenty of grip in the corners, so that wasn't the issue.

I'm stumped. Any ideas?

Thanks.

 

Pull your codes. Likely ebcm and/or steering wheel position sensor.

 

It's impossible to guess with the AH as it's so complex

Pull the codes and post up and that should give a good idea.

 

There are no codes. It wasn't a fault, the active handling was just kicking in when it wasn't supposed to. From what I understand, in Competitive Mode the traction control is disabled, but the active handling is still on. The car was not sliding and there seemed to be plenty of grip, though i was probably spinning the rears slightly. I was accelerating while tracking out of the corners when this would happen, but only on those two left handers.

 

Anyone???

 

Check your differential.

If your diff clutches are worn out it can cause that type of behavior. On tight low speed corners you are in a lower gear and have a lot more rear wheel torque, and the inside wheel wants to spin. Normally that would be controlled by the limited slip, but in this case the LSD isn't locking up and the wheel wants to spin. When it does the AH system cuts in and applys the inside rear brake.

Using active handling on the track on a regular basis tends to put a lot of wear in the clutches of the diff. I only used the competition mode once on an autocross course and you can feel the AH system cutting in and trying to straighten the car by applying brakes on the rear wheels. When that happens it is working the diff and forcing the clutches slip. After they slip too much the get worn and don't provide as much limited slip action. You will see it first on lower speed corners.

Bottom line is you have probably worn out the diff clutches and need to put in new ones.

You need to learn to turn off the nannies, and it won't be a problem.

 

The active handling has rarely interfered with all of the track driving I have done, so I don't think it put as lot of stress on the differrential, though I completely understand how it could. The only reason I use it is becasuse I am able to rotate the car withou interference, and it did save my butt once at Texas Motor Speedway, preventing damage to me and the car.

I was thinking it could be the differential clutches. Is there a way to check them without dissambling the rear end? Perhaps by flooring the car in second gear and feeling if both wheels are spinning?

Thanks for your help.

 

You can jack up one rear wheel, block the othe three wheels, release the E brake and measure the torque with a torque wrench that it takes to slip the wheel that is in the air. Be careful, you are trying to move the car and the other wheels need to be carefully chocked so the car can't roll.

I don't recall what the differential break away torque is, there is a spec for it somewhere in the manual, maybe someone who knows can chime in. Make sure you are using the torque wrench at 90 degrees to the axle. That is, if the lug nut you are wrenching on is on the horizontal, the torque wrench should be vertical. Or, if you have a big enough socket you can wrench on the main axle nut, it will take a lot more torque than you can put on that nut to break it loose than it will to spin the axle.

I was thinking it would take about 75 foot pounds, or it could be more like 100, but it is close to or less than the lug nut torque as I recall. If it's less than 75 you are for sure too loose and it's time for clutch packs.

I know a few folks who used the competition mode a lot and had to rebuild their diff's more than once because of it. What you don't realize is that every time it is applying a rear brake, it's fighting the differential clutches, so if you get into it at all, you can use up a diff pretty quickly. Best just to turn it off.

 

Thanks for the reply. I will check both sides and see if there is a difference.

As for the Competition Mode - Doesn't the DIC indicate when the active handling intervenes? I thought that as long as I didn't feel anything and I wasn't getting the message, then I wouldn't be wearing the brakes and/or differential. It definitely gave me the message when I felt it activate.

Regardless, I will probably not use it anymore.

Again, thanks for your help. I really appreciate it.

 

Yes,, I also believe it is greater than 75 FT/LBS. IF,,,,,,,, its less, you could have worn clutch packs OR a broken bellveiw spring (whick preloads the clutch packs):





If your getting an AH event, you should see the messages in the DIC. Even IF,,, AH interveined, it SHOULD NOT activate TC if you were in COPP MODE.

Try the same track events with TC and AH OFF (be careful) and see how it feels.

BC

 

I agree. The only thing I wasn't sure of was if I was getting a lot of slip on the inside tire, maybe the algorithm in the active handling was getting confused causing it to activate. I certainly didn't feel much slip before the active handling intervened and I wasn't putting a ton of power down either, which is what is confusing

I'm not going to the track again anytime soon, and there is no way to safely test this on the streets, so I will try to measure the torque to cause the limited slip to break free on each side. I have a digital torque wrench that records maximum torque, so I'll use that. If I can determine that it's broken bellview springs or worn clutch packs, I will probably upgrade to a Quaife and not worry about this again. I just don't want to spend the time and money there if it's some other problem.

Thanks for everyone's help.