Anti-lock brake question
Anti-lock brake question
(OP)
In a straight line panic stop would the anti-lock brake system keep the tires from leaving skid marks? Specifically, in a 2002 VW bettle.
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RE: Anti-lock brake question
RE: Anti-lock brake question
RE: Anti-lock brake question
- Steve
RE: Anti-lock brake question
RE: Anti-lock brake question
That said, every manufacturer obviously rolls his own algorithm to control the ABS. There may be sensor failures or processor failures on top of everything else.
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RE: Anti-lock brake question
- Steve
RE: Anti-lock brake question
RE: Anti-lock brake question
I've never had an emergency-braking-to-full-stop situation that didn't leave black stripes on the road, even with ABS (and stability control, and roll control in some cases) in several vehicles I've owned recently. The ones for which specific examples come to mind are Honda Civic, Mini Cooper, Nissan 4wd pickup, Ford Explorer, Toyota Scion Xb. In some cases I left more than 20ft of skid marks. I seem to recall having seen some skid marks with the central zig-zag patterns of the tread visible, which would suggest that the tire was rotating while leaving marks.
RE: Anti-lock brake question
RE: Anti-lock brake question
RE: Anti-lock brake question
Cheers
Greg Locock
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RE: Anti-lock brake question
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Anti-lock brake question
As the knuckles rust, it pushes the sensor away from the tone ring and the signal starts dropping out at higher speeds, until the point that the ABS starts activating during normal stops.
I'm sure there's a good reason why some manufacturers still mount the sensors radially instead of axially, but I can't think of one.
RE: Anti-lock brake question
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Anti-lock brake question
Perhaps this is only a regional problem.
RE: Anti-lock brake question
Mike Halloran
Pembroke Pines, FL, USA
RE: Anti-lock brake question
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Anti-lock brake question
Hi Mike. This is an extremely common occurrence around here. Often times removal of the sensor, and cleaning the mounting surface and sensor bore through the knuckle restores normal operation.
ABS modules are very sensitive to flaws in any of the sensor signals. If a single pulse from a sensor is delayed, or simply too weak just prior to a vehicle stopping the module interprets that as a lock-up and the system goes into anti-lock mode. Some manufactures have resorted to disabling the system at speeds of 3 to 5 mph, when a false signal drop-out is most likely to occur.
BTW the best way to tell which signal is dropping out isn't to watch the speed signals, the tech should watch the dump valve commands the ABS module issues. The brake being modulated incorrectly, is the one that the sensor is acting up on.
RE: Anti-lock brake question
"
Who doesn't? There are good reasons for disabling the ABS at very low speeds that have nothing to do with signal dropout, I would be very nervous about buying a car that attempted ABS at such low speeds.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Anti-lock brake question
RE: Anti-lock brake question
RE: Anti-lock brake question
The answer to who doesn't was just about everyone when ABS first hit the market. The Bosch and Teves systems both had to undergo changes to limit low speed ABS operation. If you want to go with generalities, most systems older than the 2001 model year would be functional all the way to a stop. It was about 2004 before cutting ABS below 5mph became the norm.
RE: Anti-lock brake question
I find it hard to believe that Australia was unique in that regard, since snow is one of the surfaces that needs low speed lockup.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Anti-lock brake question
Short return visit here, I'm not planning on spending any real time here in these forums. I just to let you know the last car that I had to diagnose for improper antilock operation was a 96 Lexus ES300, Bosch system. This vehicle could enter antilock operation inside the shop, under 3mph. The LF wheel speed sensor signal was erratic. VIN can be provided VIA e-mail if you want it.