1991 K100rs abs brakes - K-Bikes.com - Excellence in Motion
 
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post #1 of 5 (permalink) Old Jan 28th, 2013, 1:43 pm Thread Starter
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Location: Santa Barbara, CA, USA
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1991 K100rs abs brakes

Hello,
Recently put on new brake rotors and pads. Have bleed the front calipers and abs modules several times. What I still have is when you pull the front brake lever, it is firm, the bike slows down well. Just as you are about to stop, maybe at 0 speed almost, the front brakes let go for a second then grab again. You can hold the front brake lever in and the brakes let go then grab again to stop.
Anyone got any ideas?
Thanks
Duke
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post #2 of 5 (permalink) Old Jan 31st, 2013, 1:16 pm
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Location: Lebanon, OR, USA
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I am far from an expert on ABS brakes, but I would say you have not bleed all the air out of the ABS unit. It takes time and patience to do the ABS unit.

Just my 2 cents worth

2008 FLHT
2008 R1200RT
1985 K100 RT
1979 XS 650 Street tracker
Ridden everything,owned lots
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post #3 of 5 (permalink) Old Feb 1st, 2013, 8:38 am
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Just don't stop then.

(j/k)

Are you sure it's just the front letting go?

If you have air in the brakes then they'll be mushy all of the way through the travel so I doubt that's your issue. Your symptoms sound more like what I refer to as a "false positive" - ABS kicking in when you don't think it should.

Does this happen on flat, smooth, predictable pavement? Potholes and/or irregular pavement, when the rear end is getting light while braking can occasionally cause this.

Or braking coming over a rise when the combination of coming over the rise and the lightening of the rear under braking will cause the rear ABS to let go.

It may also be issues with your rear suspension.

First thing I would do is check the front and rear ABS sensor gaps.

Try braking with the front brake only.
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post #4 of 5 (permalink) Old Feb 1st, 2013, 1:08 pm
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I know the later bikes can feel like that. Mine used to but not so much anymore with much better tires. And that was mostly on "chip seal" roads, altough they have a good grip on tires, not always even if you hit loose chips. Enough of them hitting my boots in curves, they sure come loose.

Not sure about your bike/year but for sure on the later models the ABS shouldn't activate under 5 Mph or so. I carefully test that in my gravel driveway. Over 5 mph well, may not stop where you think it will on gravel.Watch out.....!

Some of them front MCs are hard to bleed if they have run dry. Because of the angle tiny amounts of air can get trapped and won't come out just bleeding.You really have to move it or the handlebars so it is as straight as possible and even the line pointing up. I have to readjust when I do that on my bike, I changed the angle of the controls and can't do it just moving the handlebars, I have to rotate the MC.

One way around that is to tie up the lever overnight and the MC straight and let the air bubbles float up. And make sure the very tiny pressure relief hole at the bottom of the MC isn't getting plugged, been a few of them like that lately.

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BMW K100RS at 27
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post #5 of 5 (permalink) Old Feb 1st, 2013, 5:07 pm
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Location: Hales Corners, WI, USA
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ABS catch & release, my 93 RS

Do what Flying duck says.

It;s not throwing a fault code yet, but it's very very close.

Mine was doing this after I had the wheels powder coated. I also had those front spacers done on the axel. The coating was just thick enough to alter the sensor gap.

First ride was AOK. Then I'm rolling up on traffic and I feel pressure on the hand lever, but the bike is NOT stopping! FARK!!! Hard on the rear, hard on the front brake and the front engages hard, very grabby. Seemed like low speed modulation at the hand lever was way way off.

The front brake worked fine if applied firmly. But in stop & go traffic it was hard to be smooth and easy. Not at all like it was before I did the powder coating. So adjust my riding a bit to compensate and after a couple days I get the ABS light show. I forget the fault code number, but I found the plug near the front of the battery and made a LED tester to find it. Sure enough, sensor fault gap.
I shine a very bright light from behind and notice that the gap from ABS ring to sensor does look wider than I remember. So I take off the senor and pull out a .012" spacer. There was a stack of three or four in there. Put it back together, clear the fault code, and all is as it should be.

What you are describing sounds just like what I had.
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