ABS activating when coming to a stop

In the last few days, the front ABS has been activating when I'm almost at a stop (down to maybe 2 or 3 mph), which then releases the brakes for just a fraction of a second and allows the bike (2000 R1100RT) to lurch forward. I can control it by using the rear brake simultaneously, but it's a little annoying.

The only thing I had done on the brakes just prior to this happening was to take the two brake cylinders off and, to be able to remount them on the rotors, pushed the brake pads apart a little to get more wiggle room. Could the ABS lurching be related to some air having gotten into the system, or is this likely unrelated and some other problem? Or is it even an indication of impending brake failure? Any ideas or experience with this out there?

My bit...

I would do an abs bleed first (front and rear), then the rear caliper, then left side, then right. since you have the tank off, unplug the ground on the battery for a few minutes then reinstall. Then perform an abs reset. Then test ride. Maybe half hour of work. If you don't know your bike well, you will be a little more confident when you are done........especially if this works for you. Thing is, you will have performed so many steps, I don't know if you could tell which step made the correction. Best of luck -Matthew

Power Bleed

I intended to change the brake fluid anyway, so this is a perfect opportunity. It's my understanding you need to perform a power bleed on this bike, and I have no idea how to do that, so I probably have to take it to the dealer. Unless someone has instructions somewhere on how to do that without the computerized system the dealers use... If anyone has instructions, or a link to them, I'd be very interested.

I have a 94 R1100RS, which I think is the same ABS unit as on your bike. I have taken the calipers off many times to remove the front wheel assembly. Each time I push the pads back into the caliper in order to be able to get the calipers out of the wheel.

I have never had a problem as you describe in 15 years and 140k+ miles. But if your brake fluid has never been flushed and changed, then yes it definitely should be done. I have bled the brakes on my RS maybe four times in all those years and I've done it myself every time with common hand tools. I do use SpeedBleeder nipples at the calipers which makes brake bleeding very easy.

ABS faulure or problem, Step one every time

Please report ABS modulator failure to the NHTSA-the life you save may be your
own. Call The Office Of Defects Investigations at (888)327-4236 orTTY (800)424-9153

Its better to get them on line, here is the link:
http://www-odi.nhtsa.dot.gov/ivoq/Rep

Here's a link that you can use to learn about bleeding the brakes. See Andy Long's post.
http://bmwsporttouring.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=494710&gonew=1#UNREAD

Vaughnb said:

Please report ABS modulator failure to the NHTSA-the life you save may be your
own. Call The Office Of Defects Investigations at (888)327-4236 orTTY (800)424-9153

Its better to get them on line, here is the link:
http://www-odi.nhtsa.dot.gov/ivoq/Rep

Click to expand...

what makes you so sure this is a modulator malfunciton?

pressing the pads into the calipers did not introduce air into your system (unless you have a torn seal, and even then not too likely), nor is it real likely to be the culprit in this instance. do a fluid flush, see what happens.

Before you go too far tearing stuff apart, make sure your front brake ABS ring doesn't have a ding in it. This is not that uncommon, and can cause just the symptoms you mention. I have seen it twice, and once the dealer had told the owner that he needed a new ABS unit.

Jim

I agree on the ring damage possibility. The tooth wheel on my 94 R1100RS is the heavier, older style which is either machined or some sort of pressed steel ring. Pretty hard to damage it.

But later models had a stamped steel tooth wheel, much lighter, but also easy to bend or damage. If the ABS tooth wheel has damaged, dented or missing teeth the signal from the speed sensor to the ABS computer will fluctuate. At higher speeds the fluctuation is extremely brief so the ABS computer will not react to it. Also, for the ABS to engage, you have to be on the brakes, like slowing for a stop. At slower speeds, like almost coming to a stop, that fluctuation could be enough. Lets say an area of ten spaces on the tooth wheel got dented in. When that section passed the sensor the ABS computer will see that as a wheel speed suddnely slowing during braking, especially if the signal strength drops (which it would). The ABS would engage and release that brake.

I agree, check the ABS tooth wheel attached to the front rim and make sure all the teeth (or gaps) are equal, and all the same distance from the sensor tip. Even a gap of .125" could be enough to trigger a fault.

Norton, thanks for that excellent link. I've got a 2004 R1150RS. Do you (or anybody) know if this procedure will work on my bike? Looks to be the exact same setup as the RT.

beemermyke said:

Norton, thanks for that excellent link. I've got a 2004 R1150RS. Do you (or anybody) know if this procedure will work on my bike? Looks to be the exact same setup as the RT.

Click to expand...

Should be the same. See also:
http://http://advwisdom.hogranch.com/Wisdom/service_abs3.pdf

Note: Instead of DOT 4 you can use DOT5.1 - this stuff does not attack paint. However, do NOT use DOT5 - that's not compatible.

The instructions look quite complicated but really are not. Read them over carefully and follow them step by step. After you have done it once, it becomes logical.

Finally, you may want to replace your bleed nipples with speedbleeders. At $7 a piece, that's a good investment. Just make sure you get the proper size - the website is not always correct in its recommendations.

Good luck!

Yes, DOT 5.1 can be used in place of DOT 3 or DOT 4. But the only gain is the higher "Dry" and "Wet" (wet meaning after the fluid has built up some water content) boiling point of the brake fluid. If you live or ride in the mountains with many downhill heavy braking sections there is a potential performance gain with DOT 5.1, but only if you are getting your brakes really hot on a regular basis.

Otherwise the only other gain is it does not attack paint like said. From past experience, when I didn't know, NEVER put DOT 5 fluid in a brake system designed to use DOT 3 or DOT 4 brake fluid. The DOT 5 silicon based fluid WILL damage and swell all the seals in the brake system. Most likely you'd get severe brake dragging issues. It will also attack the inner tube of the standard synthetic rubber brake hoses.

IMHO you do not need the speedbleeders with the servo-ABS. Not only that, but they tend to be soft and can break easily, plus do not always fit like they should.

Jim