K75 ABS weirdness - SOLVED

[Motorhobo]

I'm glad this worked out the way it did but I'm not sure I understand it.

In March I rebuilt the front and rear calipers on my 95 K75 zombie and replaced the lines with Spieglers. That entailed also taking off the ABS sensors. When I got everything back together and rode, the ABS light flashed until I hit 72mph then went out. Not good for in-town riding where the speed limit is 25 if you have to get it up to 72mph to activate your ABS.

A couple weeks ago I got the tranny and rear end back on and rode -- again, light went out at 72mph. I hadn't touched the calipers or drained the rear brake lines for the rear end work, just bungeed everything
up and out of the way.

A buddy of mine suggested that when I rebuilt the calipers I might have misinstalled the shims under the ABS sensor which was giving faulty readings below a certain RPM and that I'd have to remove the sensor and make sure the gap was within tolerance. Getting that sensor back on is a PITA so I decided I'd do that later when the bike was back on the road so I could read out the fault codes.

I proceeded then to pull off the front wheel to paint the fork sliders. When I got it all back together yesterday and rode, lo and behold, the ABS light turned off immediately as soon as bike started moving as it is supposed to. So -- all fixed and I didn't have to fix it! A miracle.

But not being one to believe in miracles on the K-bike level, I am curious as to what happened. Prior to this, the front calipers were installed properly with the mounting bolts torqued to spec. All I did was remove calipers from the wheel and put them back on. I also washed the wheel but didn't scrub down the ABS disk. Anyway, I thought this would be worth sharing and maybe someone has an explanation that might help someone else out later on down the road.

Van

[Motorhobo]

After talking to my K-Bike guru and ex-BWM mechanic Mike, I think this issue is resolved. Here's the deal --

The ABS sensor gap has to be within a certain tolerance in order to provide accurate information to the ABS brain. In my case, the gap was off by some micro-millimeter increment. This resulted in incorrect data at the brain which resulted in the brain not being able to correctly interpret the data. The result was that the ABS fault light flashed until I reached a specific speed, in my case 72mph. At that point, for whatever reason, the brain was able to recognize the data and the ABS was activated.

If that happens to you after you remove and reinstall your front wheel or calipers, try this procedure for properly installing the wheel to ensure ABS functionality:

1) Put on the wheel and calipers leaving all the bolts loose.
2) Make sure the caliper pistons are retracted all the way in the bore. I pushed the brake pads back with a screwdriver, Mike says you can do it just by rocking the calipers on the disk.
3) Tighten the hex nut on the axle to spec.
4) Tighten the clamp bolts adjacent to the hex nut to spec.
5) Bounce the wheel up and down a couple times so that everything self-centers.
6) Tighten the clamp bolts on the other side.
7) Tighten the caliper mounting bolts to spec.

When the caliper bolts are loose there is a tiny bit of play that can affect the ABS sensor gap. If you get an ABS fault after installing the wheel, you might be able to fix it just by loosing the bolts and following the above procedure.

I'm not an ABS expert but all I know is that my ABS works properly now whereas before I had to break speed laws to get it to activate. I don't mind breaking speed laws but there are better reasons to do that than just to get the annoying light to stop flashing.

Van