ryoung

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I haven't been on a track since Mid-Ohio about 6 weeks ago, so I thought it was time to remind myself what maximum effort braking feels like.

So I'm driving down an Interstate with no traffic when I see a straight and downhill exit ramp ... I exit at 75 mph and get hard on the brakes. The car stops staight and true like I threw out an anchor, but I hear the tires screeching and don't feel any ABS pulsation in the brake pedal. I look in my rearview mirror and see two long black steaks of rubber from my locked tires.

The ABS system was definitely working at Mid-Ohio, especially after the S-03 tread temp hit 240oF and they got a little greasy. The ABS light is not lit when I'm driving, but it does come on for 1-2 sec like it should when I start the car, so the bulb isn't burned out.

Anyone ever seen this or have any ideas?

April

I seem to recall a post on the A8 or A6 forum like yours. Search there ?

ryoung

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in the threads I found, the failures were all accompanied with the ABS light coming on.

April

I've never heard of a system that doesn't give an indication when it has a fault. You might check Stoney's posts. I know his ESP wasn't working, and the warning light never came on.

Interesting, but likely not useful in this case:

http://www.bba-reman.com/hints_and_tips.htm

PaulW

I think you mentioned that you didn't have the ross-tech tool, that's the first thing I would check are the codes. If there is one, just look it up in the table. Your car is still under warranty, isn't it?

ryoung

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Yep, it's still under warranty; and I have the 20k mile service scheduled for this Friday, so the dealer can look for any error codes.

Still, I do need to order the Ross-Tech software for days like this. I'm really surprised, though, that something like this could happen without tripping the ABS light. I expect that the ABS system is probably about the most completely monitored system in the car.

ryoung

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ESP on his A6 was activated and working, but the ESP light never came on.

In my case, I would have thought that a failure that prevents ABS from working would trip the ABS warning light.

BTW, from digging around, it seems that most ABS failures are associated with the wheel speed sensors -- dirty, broken wire, etc -- but these failure do trip the ABS warning light.

skiracer

According to the Bentley, your ABS system uses fuses S9, S7, S10, S53, and S54. all located in the front passenger footwell. However, since you are still under warranty, I would let the dealer figure out the problem!

2001 A8L

I know that this might sound strange but ABS is being refined every few years to provide shortest stopping distances in most any condition....what this means is friction needs to be maximized...a full lockup of all wheels would provide the shortest stopping distance on dry pavement...perhaps on wet too but at the expense of loosing control.

People use to complain about ABS because it would not allow them to stop in the shortest distance possible which might lead one to impact something although it would be nice and straight when it impacted.

I have experience lockup on ABS equipped Audi's when in an emergency brake maneuver...you can even hear the tires as they lock and loose rubber on the pavement.

The intent of ABS is to maintain control of said vehicle without loosing control of steering while providing the shortest stopping distance possible...the more ABS gets refined the better the control and the shorter the stopping distance...locking up brakes is the shortest stop possible in many instances...keeping the vehicle from loosing control is more the objective now...

I'm not saying don't have your vehicle checked but don't necessarily generalize that lockup is not possible or should not be possible with the newer ABS systems. This is especially the case with ESP equipped systems that can combine technology to maximize control...

Also consider if you have modified your vehicles brake system from stock that the ABS may not work exaclty as stock...I have heard of Big Red Porsche upgraded vehicles that had issues with ABS regulation due to the massive brake capability on one axle...i.e. the front axle and the ABS system is forced to lock the rear to prevent it from coming around...

April

seemed to be working ( to some degree ), but there was no light. I'm not sure just well it was working, as I wasn't driving, but it seemed like Stoney could do all sorts of things that the ESP would normally cut back when encountered.

My '80s vintage Alfas are always having ABS system issues ( nothing like current systems ), but the light always works unless the bulb burns out;-)

You have a real head scratcher. Please let us know the outcome.