Driving home on I-93 from the White Mtns, NH, last week doing 80 mph in the left lane, I experienced an idiot 2 cars ahead making an illegal U-turn in an unauthorized U-turn opening. I had to get on my brakes very hard to slow to less than 30 mph. As a wheel or wheels started to lock up, I started into a left skid, with the rear fish-tailing right. I realeased the brakes in time to correct the skid, and fortunately had slowed enough to avoid a rear-end collision wit the vehicle ahead. No, I hadn't disconnected DSC; it should have been working, as well as ABS. Very hair-raising situation!!!
The Z8 went into the service dept (to correct the sticky accelerator pedal and moisture behind a tail-light lens). They checked out the ABS when in, and reported no problems. Naturally, they didn't perform an emer. stop at 80 mph.
Part of the problem may be the run-flats, which are reportedly not as sticky as, let's say, the Pilot Sports, but a functioning ABS should have prevented the skid.
I plan to attempt another high speed stop (on a quiet stretch of the interstate in MA to make sure ABS is working before I assume all is OK.
Have any of you experienced this pbm with your M5/Z8?
I had two lockup experiences when I jabbed the brakes short and hard to cut speed. What was a bit scary was that as I released the brakes the lockup continued for a fraction of a second. I'm using aftermarkrt AP brakes but I dont see why this would make a difference.
Have you made any upgrades to your brakes? Stoptechs, etc?
Also, if the road is slick enough, the wheels will still lock up some even with ABS, but it shouldn't be enough to start a slide. You might want to try it again under controlled circumstances and see if you can reproduce it. If so, I'll get back to the dealer ASAP.
Re: Partial Wheel Lockup - Braking Hard From 80 MPH
Hello DrRobb,
Quote:
Originally posted by DrRob As a wheel or wheels started to lock up, I started into a left skid, with the rear fish-tailing right. I realeased the brakes in time to correct the skid, and fortunately had slowed enough to avoid a rear-end collision wit the vehicle ahead. No, I hadn't disconnected DSC; it should have been working, as well as ABS. Very hair-raising situation!!!
What were you doing with the steering wheel while this was going on?
In other words, was the road straight, were you trying to get into another lane, etc.?
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2002 LeMans blue sport w/silverstone & faux aluminum trim
Right KGK, I was thinking the same thing. The 911's (very old ones) used to have a big problem swapping ends on hard braking (not just lockup). With that much rear weight bias, any lateral force at the time of braking would tend to want to carry that weight right around.
I've been on the track with the M5 at Sebring and had an instructor say they heard the ABS cycling when braking hard coming down from 130mph. You have to have the car going perfectly straight before you apply that 10/10ths braking or you will definately feel it trying to go sideways.
Dr. Rob, I'm guessing the car was not totally straight in your situation, but I would test it again as you mentioned.
Wow, that must have been a hair raising experience. This should definately not happen with ABS in the car. Maybe something clogged the brake line, a piece of rust or metal, and caused the brake to lock up? I really could not understand how it could happen on such a new car but it does happen quite a bit on older vehicles. I think you have been hanging around with too many Vipers . Definately get it checked out asap.
I had the car checked out 3 days later; no problems found, and as it's new, I doubt if that's the problem.
Phil and Basil,
No aftermarket parts (except a suctioncup-mounted battery powered Escort Solo). The road surface was perfectly dry and no evidence of it to be slick, as I recall. I did wonder about the stickiness of the run-flats, but on previous hard acceleration runs with DSC engaged, I never experienced the DSC kicking in (by both feel nor dash indicator warning lamp).
kgk and Aussie,
The road was perfectly straight. I was in the left lane all the while, and the panic stop was (should have been) a straight line stop - no wheel turn - as I had no lane to change into, as there was traffic to my right.
I'm not sure about the M5 equipment, but the Z8 ABS also contains the system called Dynamic Brake Control (DBC), which produces maximum braking force boost and helps achieve the shortest possible braking distance.
TC
I haven't encountered another Viper since my last experience, they're a rare bird in NE, as is the Z8.
When I get a chance under the right conditions, I'm going to repeat a hard braking situation and see what happens.
Rob,
I had a little lock up in the M5 in a similar situation, but the car stayed straight. I was surprised that no abs came on. I then was able to try this under controlled conditions and could not repeat it. Ive never had this in the Z8 and Ive had a few similar situations at around 60mph. Glad youre AOK!
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All the best,
Jerry 00 Z8 Jet Black/Red Sport / some others
DrRob;
The Z8 should not do that. Its braking should be as good or better than the M5. I was able to test the brakes on my M5 from 100mph and more on the track. I was to the point of ABS kicking in on some of the stops with no ill effects. I also determined the threshold point (just shy of lock up and ABS kicking in) on the dry track and stopped that hard time after time with no problems. Since then on the street I've not had to do a full on panic stop but I've nailed them hard from 80 mph on several occasions to test the threshold point. On rare occasions I may notice a slight sideways weight transfer but nothing remotely close to causing a skid. I've felt it far worse on other cars I've owned. I've always wondered if cold brakes and a slightly sticky piston might cause a delay of one brake to come on, leading to a sideways weight transfer and in extreme cases a skid. However, ABS and DSC certainly should catch all but the most extreme situations.
BTW, the M5 does have dynamic brake assist. I think I can feel it squeeze the brakes a bit extra on hard stops. The '99 540i also had it and it was really noticeable on that car, almost like somebody stepping on your foot to push the brake harder.
Have you done the Z8 Experience? At the M5 DE, we did repeated ABS stops from 60 in the wet in a turn. Absolutely no drama or attempt to skid sideways.
About your situation, you could try some hard brake tests on a quiet stretch of road. I would try various moderate, hard, and possibly full on stops with cold brakes and repeated tests. If you consistantly get the odd feeling of a sideways weight transfer, I'd have the brakes looked at closer. Otherwise, it might have just been a fluke based on certain conditions.
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As a wheel or wheels started to lock up, I started into a left skid, with the rear fish-tailing right. I realeased the brakes in time to correct the skid, and fortunately had slowed enough to avoid a rear-end collision wit the vehicle ahead. No, I hadn't disconnected DSC; it should have been working, as well as ABS. Very hair-raising situation!!!
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. Definately get it checked out asap.
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