bart1

1995 C4
ABS/ABD
Stock calipers
New Pagid Yellows
New Falken RT615s
New ATF Gold
ABS/ABD module was replaced a couple years ago.

That's my setup, figured there would be questions.

At my track day last weekend, I got into the ABS twice. The first time (unless I was just teetering on the limit of grip), it seemed to work as normal. As the day went on, I was carrying more speed deeper into the corners. Toward the end of the day, I got a pretty hard lockup on both front tires. I was able to manage it with no issues, but lost momentum on that turn I haven't tried to lock them up since then, but I did confirm that at low speed my ABD was kicking in with wheelspin.

I have no ABS warning light or anything else unusual. I called my mechanic and he said to let him think about it. He has never had to troubleshoot a system with no warnings showing.


Any ideas or next steps in troubleshooting?

Thanks!

-Bart

bart1

Oh, on a totally far removed, unrelated topic, is there a better way to get rid of flat spots other than driving on them or having them shaved?

Stuttgarter

Bart,
I'm a former ABS engineer. What you are describing should not be possible. Can you confirm that the ABS light is working? Does it come on when you turn the key from off to on? Can you find a dirty or gravel road to test the ABS without hurting the tires too much?

bart1

That's what I thought, Stutt. If the ABS sensor was getting no signal, I should have a warning light. I am almost positive that the light works when key is turned on, but will confirm. Note that I did get the flashing ABD light when I spun. I did get significant lockup at the track, but checking the light was low on my priority list at that point. . I'll try to get some lockup and test sometime.

You from Stuttgart? I'll be over there next month.

Zba

For your flatspots, inflate the tires to maximum pressure then drive and get the tires nice and hot. Then deflate to around 20-25psi. Drive again, getting them hot. Fill the tires to normal pressure and drive again to let them cool. This may help.

bart1

Thanks, Zba. Maybe I'll try that. I left my tires on there and have driven on them a bit and it's almost gone now.