LappDog

I have an '03 ZO6 that I have been tracking for 3 years. I have been using Hoosiers, HT-10 brake pads, along with Motul with very positive results. (Won my division for 2 years). Last year the rules were changed and I needed to get on less aggressive tires if I did not want to be bumped into a higher group. I chose RA1's (275x40x17 & 305x35x18)as the stagger and weight was very close to stock. I also added QA1 adj. shocks. My problem is the ABS is kicking in braking into corners, lengthens my stops, and I am running off the track! I have played with different settings on the shocks (currently 9 fr and 8 back) but no change. Tire pressures are about 40 hot. I was told if I disconnect the ABS at the wheels the car will not drive over 50mph. Thanks for any suggestions.

AU N EGL

When was the last time you changed your bearings?

LappDog

Never. They don't seem to be noisy or show any play

0ATI Performance

If you want to try driving the car without ABS, simply pull the ABS fuse (in the fuse box under the hood, it is one of the big fuses, look on the chart inside the cover). The IP will complain, but other than that the car will drive fine. I never heard of the 50mph limit, that is not true. Simply plug the fuse back in and reset codes to go back to ABS.

If your car has dynamic rear brake proportioning (and not a mechanical proportioning value) you may end up with too much rear brake bias and need to compensate with pads or other means.

Bob

TommyBoy72

I dug up this older thread because I am experiencing the same issue. I am on 275/40/17 and 315/30/18 Kumho V710s. The best description I can think of is that the ABS is going into something like ice mode. It makes me go 5-15 ft farther than needed and screw up that run. I have only really noticed this on race tires but I haven't had a big need to try this on street tires.

I PM'd the original poster to see if he found a fix. Otherwise does anyone else have lead as to what my issue might be. What drives me crazy is trying to figure out what consistently causes this. It seems to be when the braking brings me down to lower speeds, under 25mph and the braking is a stab at the pedal rather than something smoother - and the braking is always in a straight line.

davidfarmer

I have never heard of this. So your ABS isn't failing, but is OVER-compensating???? Are you sure the slicker tires aren't just locking up much easier than you anticipate compared to the stickier tires??

Ideally, you want the ABS to kick in EVERY time you hit the brakes hard. It is a really good system when it works, and can out-brake a human when working properly.

Has ANY electrical work been done on the car(s). I had a racing friend once that wired the left side to the right side, and vice versa. SO every time they hit the brakes, the computer thought the wrong tire was locking up, and releasing pressure on the NON-locked tire. Needless to say, this was not good....

TommyBoy72

Imagine you are under hard acceleration from 25-45 and then hit the brakes as hard as you can. The car brakes very hard from 45-30 and then relaxes the clamping pressure so you are braking under less than maximum potential and thus miss your turn-in point because you are going too fast to make the turn. I at first thought maybe I had put too much steering input under braking causing some lock and the longer braking but when it happened again I was careful to keep the wheel straight and it had no impact.

The ABS system when this does not happen is fantastic, no issues about when the system works. As far as I know the car has had no electrical work done. It does not seem to suffer from this while braking at higher speeds, it only seems to happen when braking hard in 1st gear.

Doing some searches on z06vette.com show people talking about this but almost no info on this website. Weird.

VetteDrmr

I've had ABS give me some grief, but different from your description.

My case would happen when I'd be at fairly high speeds (e.g. the top of 2nd), and I would stab the brakes hard. The pedal would immediately push back and I'd have to *really* stand on the pedal to get whoa'd up (sorry, TX jargon).

I found that if I took about a half second to apply the brakes, I almost never have that problem. I can still feel the ABS vibrating against the pedal, but not the major pushback.

I've never had the brakes release pressure *after* the speed's been hauled down.

HTH, and have a good one,
Mike

davidfarmer

well, the first issue sounds like the ABS controller is mis-reading lockup, or one of the valves is releasing pressure on it's own. Have you tried having the ABS system blead with a tech2? I doubt it would help, but if there is an air bubble in one of the valves, I guess it could cause the valve to flutter when it opens??!!...

As for the pedal pushing back, I'm not sure what that could be. I assume the ABS valves re-set between hard brakings, which would indeed push fluid backward in the system slightly. Again, I wonder if the system thinks you've stopped braking when you haven't.

Either of you guys ever have ANY ABS/TCS trouble codes?? Also, do you run traction control on at all??

VetteDrmr

Maybe "pushback" was a bad term. More specifically, it's like the brake pedal engages and gets very hard very fast, more so than normal.

No codes, TC/AH off, old-school brake bias block, and I can still get good braking, I just have to use probably twice the normal pedal pressure to get it.

What's interesting is that, if I smoothly depress the pedal it goes down further and I can feel the ABS working (that vibration feel). So, I think I've just learned how to brake better.

Thanks for the help, and have a good one,
Mike

TommyBoy72

This is I think potentially the common link. Maybe because of the abrupt braking we are unloading the rear enough its causing the ABS to engage and it simply isn't adjusting the weight transfers rearward. A quick but more gradual application avoids the issue? In the Miata (no ABS) this was by far the best technique to get optimum braking especially with the stock proportioning valve.

My weakness is I've never really raced a car with ABS so I'm not used to just standing on the brakes for a stop. It is very possible I'm at fault because I am doing a violent stab at the brakes.

Bill Dearborn

Could it be that you are not experiencing brake release but an ABS failure where it is allowing the wheels to completely lock up? This would cause your stops to extend quite a bit. I had this happen on my 97 due to a problem in the EBTCM. I came into an autocross gate at about 70 mph where I had been previously hammering the brake to use ABS to slow the car and then turned when I reached my turn in point. After doing this 5 or 6 times I came up to the gate, hit the brake and slid completely past the turn in point before I realized what happened. It felt just like I didn't have any brakes. A friend video taped the whole thing and it showed I really smoked both front tires.

Bill

Todd Z

I had the same problem with the same tire set up. It turned out to be the YAH sensor. I am not sure on the spelling.

davidfarmer

yaw sensor should effect ABS, only active handling/traction control. That is why I asked if they are driving with AH/TC turned on. With those systems shut down, only the wheel-speed sensors are involved.

Stabbing the brakes is the perfect way to drive ABS. You shouldn't have to wait before applying the brakes. I don't know what it is, but there is a problem.

The only ABS issues I've ever had is simple FAILURE due to a sensor wearing out, or cutting a wire. You get a warning on the DIC, and if you overbrake, you'll lock a tire...simple.

TommyBoy72

TC/AH is always off when it happens.

I checked and I have no codes even in history related to ABS.

I agree it would be strange for the YAW sensor to be needed in ABS? Does it calculate YAW with rotational speed of each wheel to help it figure out the difference? The hard part is replicating the issue. I don't exactly threshold brake 6 times in 30 seconds any other time. And then to find a place safe enough to do it in case it does go long.

The only thing making sense from all the feed back is that indeed a tire is locked up. But again I would think the ABS would figure this out and let that wheel spin and then brake it again?

varkwso

I had the ABS code come up on the DIC at CMP (AH/TC off) on the ZO6 on the pit straight and smoked a front tire braking for T1 . After pitting out and resetting the code I have not had any ABS issues with the car at the track. Wheel bearings are fine.....

A few months before we had real ABS issues with the FRC at CMP behaving squirrelly. In the end it worked out, we think, to be new pads (XP8s I believe) and crappy old tires (even crappier than my norm) that were the source of the problem. Fresh tires solved the problem that weekend.

If you want to troubleshoot a brake problem just go to CMP

TommyBoy72

Ok, I feel dumb for not remembering this. I did change out all four shocks prior to the first event on race tires and noticing this issue. Could I have bumped an ABS sensor in any fashion that would not trip a code but cause less than ideal performance? Do the sensors ever need to be cleaned?

varkwso

possible but not real likely..

Jaymz

I dont believe that you can clean them as they are inside of the hubs which are sealed and can't be taken apart easily. if you have a bearing issue you will see C1232 - C1235 codes.

I would pull the codes to make sure there hasn't been one set.

davidfarmer

You could have tugged a wire loose, or cut it, but the bearing is sealed. However, that would set a code.

I'm stumped. Unless you got a bad valve in the ABS module, which I have no idea how to diagnose, then it must be user error

I'm kidding of course