ABS Problem - 1992 K75RT

[Inge K.]

Got back to the garage and hooked up the LED. 3 blips again = front wheel sensor fault.

And you counted the times the LED did go out, and not the flashes?

[skidmore]

Correct. It went out 3 times.

I rocked the ABS switch back and forth a couple hundred times with no improvement. I am not sure how to remove the switch from the console pad. If I got it removed, I am not sure it could be cleaned. Can anyone confirm?

[Scott_]

Yes, they can be cleaned. You must be very careful on dis-assembly as there are springs and contacts that will try to lose themselves in the process.
Check the lieberry for Duck's switch rehab thread.

[skidmore]

Liberry....on my way. Thx Scott!

[rbm]

I checked sensor gap before and after wheel re-seat. Clymer calls for .020 - .022 inches. A .022 feeler slid in with minimal to arguably no resistance. A .024 fit as well. I checked in several locations of the ABS cog by rotating the front wheel. The gap seemed consistent.

Haven't you just confirmed that the gap is too large?  Hence the ABS fault.  A 0.24" feeler should not fit; a 0.22" should be tight; a 0.20 should slip in with minimal resistance.  You need to close the gap to 0.20".

[skidmore]

Correct, .024 slid in with little resistance.

I agree, based on the findings, it appears to be a gap problem. The problem I have with that problem is why now, why after 20+ thousand miles of owning the bike does the ABS decide to fault due to improper gap? The sensor has never been removed under my ownership. The caliper has been unbolted 2 or 3 times (tire changes etc) but its location cannot vary due any sort of human error. It bolts to the fork slider and that's that. The sensor bolts to the caliper and that's that. Per the Clymer, one of the caliper mounting bolts is unique and if not used in its proper location can throw off the ABS sensor. I didn't know that until reading the manual the first time I removed the wheel (6-8,000 miles ago). (This is my first ABS K bike). So anyway, once the sensor is shimmed for proper gap, that's that.

It seems more likely that a "too little" gap condition could occur based on some road crud building up on the ABS cog than a "too much" gap condition. Perhaps the gap has been beyond the high side of the tolerance for years and years but somehow managed to work without faulting? It seems like the temperature swing from extreme season to extreme season would cause the gap to fluctuate. Maybe I'm wrong about that though. Or am I? Would the gap be the same measurement in the dead of a 100 degree Summer day in the direct sunlight as it would be on a 40 degree day in the middle of March? Dunno.

The .024 gap is a red flag for sure. Maybe the sensor itself was dirty to an extent and maybe me sliding feeler gauges across it has cleaned it up so to speak. Dunno. I'm kind of off on a tangent now what with trying to get my ABS rocker switch to work. If I can get it to work and get the ABS reset, maybe my suspected gap/sensor problem will magically go away. Dunno.

The electrical connector could be throwing the fault. I haven't pulled the tank and checked it out. It seems to disappear under the tank. Or maybe the sensor is legitimately bad. Still gots some work to do...

[Scott_]

Removing the wheel/tire can cause issues with ABS sensor gap. BTDT. I know it shouldn't but......  .02 isn't much when it comes to electronics sensitivity.
I've had to adjust the gap on mine a couple if different times after a wheel removal. Either to change the tire or to replace fork seals.
You will want a very clean torx tool to remove the screws, it will help if you soak them with a little penetrating fluid for a bit if you haven't had them out before.

[Motorhobo]

I'm still wondering if the 'rock hard lever' event is the cause and the ABS is the symptom. Something changed in the system at that point. Maybe if someone could explain how an ABS malfunction could result in that behavior. You loosened the calipers when you did the wheel re-center thing? Once I neglected to do that and it resulted in a fault.

But anyway, I remember 10 years ago I had an ABS fault and took it to an independent BMW tech, one of the old school guys who was laid off by BMW when they changed their 'business model'. He traced current in the cable to the sensor, found a break in the wiring, spliced around it, and it's been good since then. Every time I remove the FD still see the electrical tape at the splice point.

[Scott_]

I'm still wondering if the 'rock hard lever' event is the cause and the ABS is the symptom. Something changed in the system at that point.

I think there are 2 different issues, but I guess at this point, until he has the sensor issue corrected, we won't really know.
My original thought of the 'rock hard lever' is an obvious restriction in the ABS modulator, but I wouldn't think that the modulator would operate until after the system test is passed, which isn't happening yet at this point with the faulty sensor gap.

[rbm]

Correct, .024 slid in with little resistance.

I agree, based on the findings, it appears to be a gap problem. The problem I have with that problem is why now, why after 20+ thousand miles of owning the bike does the ABS decide to fault due to improper gap?

Official BMW workshop manual recommends checking and resetting the gap (page 5.18)

* removing and installing the front wheel
* detaching and attaching the sensor
* detaching and attaching the front brake disk holder

Instead ask how did I get away with not doing this re-assembly check in the past?  Luck may be the answer, that the sensor's signal was just clean enough to scrape by but age has taken its toll.

[skidmore]

Removing the wheel/tire can cause issues with ABS sensor gap. BTDT. I know it shouldn't but......  .02 isn't much when it comes to electronics sensitivity.
I've had to adjust the gap on mine a couple if different times after a wheel removal. Either to change the tire or to replace fork seals.
You will want a very clean torx tool to remove the screws, it will help if you soak them with a little penetrating fluid for a bit if you haven't had them out before.

The Clymer lists several BMW part numbers of various shims. Silly question: you used official shims I suppose? I don't have any on hand and would have to order them.

I have never laid a tool on the sensor mounting screws. I have read they are a royal bitch to bust loose.

[skidmore]

I'm still wondering if the 'rock hard lever' event is the cause and the ABS is the symptom. Something changed in the system at that point. Maybe if someone could explain how an ABS malfunction could result in that behavior. You loosened the calipers when you did the wheel re-center thing? Once I neglected to do that and it resulted in a fault.

But anyway, I remember 10 years ago I had an ABS fault and took it to an independent BMW tech, one of the old school guys who was laid off by BMW when they changed their 'business model'. He traced current in the cable to the sensor, found a break in the wiring, spliced around it, and it's been good since then. Every time I remove the FD still see the electrical tape at the splice point.

Yes, loosened the calipers when I re-center thing.

[skidmore]

I'm still wondering if the 'rock hard lever' event is the cause and the ABS is the symptom. Something changed in the system at that point.

I think there are 2 different issues, but I guess at this point, until he has the sensor issue corrected, we won't really know.
My original thought of the 'rock hard lever' is an obvious restriction in the ABS modulator, but I wouldn't think that the modulator would operate until after the system test is passed, which isn't happening yet at this point with the faulty sensor gap.

I agree; the rock hard lever made me think the modulator had whacked out. I rode about a mile on down the road before I was able to get safely to the shoulder. I killed the engine before restarting and taking off. The light was flashing and the lever still hard. A couple miles down the road and it had cleared itself and I had normal front brakes. It faulted again rather quickly but cleared again and I had brakes the rest of the way home. The following day I cruised back roads at 40mph'ish. I logged 100 miles before it faulted and stayed faulted BUT at least I did have front brakes. Hell, I rode another 30 or 40 miles just to burn off some of my gas because I anticipated having to remove the tank. The entire 30-40 miles were with ABS fault but my front brakes were normal.

[skidmore]

Correct, .024 slid in with little resistance.

I agree, based on the findings, it appears to be a gap problem. The problem I have with that problem is why now, why after 20+ thousand miles of owning the bike does the ABS decide to fault due to improper gap?

Official BMW workshop manual recommends checking and resetting the gap (page 5.18)

* removing and installing the front wheel
* detaching and attaching the sensor
* detaching and attaching the front brake disk holder

Instead ask how did I get away with not doing this re-assembly check in the past?  Luck may be the answer, that the sensor's signal was just clean enough to scrape by but age has taken its toll.

Page 5.18 of which manual? I mean, there is the PDF download here on motobrick of the factory manual but it is dated 1988 and mentions nothing about ABS. If you have an electronic version of the manual you're quoting, I would gladly accept a copy - if you offer, that is 

I understand and appreciate the need to check the gap when performing the operations listed above. Makes perfect sense to ensure proper gap and proper function of the ABS system. I suppose as an ABS bike owner, I need to wrap my head around the need to have shims on hand in case the gap needs reset.

[Scott_]

Removing the wheel/tire can cause issues with ABS sensor gap. BTDT. I know it shouldn't but......  .02 isn't much when it comes to electronics sensitivity.
I've had to adjust the gap on mine a couple if different times after a wheel removal. Either to change the tire or to replace fork seals.
You will want a very clean torx tool to remove the screws, it will help if you soak them with a little penetrating fluid for a bit if you haven't had them out before.

The Clymer lists several BMW part numbers of various shims. Silly question: you used official shims I suppose? I don't have any on hand and would have to order them.

I have never laid a tool on the sensor mounting screws. I have read they are a royal bitch to bust loose.

It appears that your gap is wide.
1st thing I would do is to remove the sensor and shims, and clean the surfaces very very good. There shouldn't be any corrosion build-up, but you never know.
Don't be surprised to find corrosion in the "hole" that the sensor fits into, it will make it hard to remove the sensor. Be patient, be very gentle but firm if you use any tools on the sensor to aid in the removal. The longer you can soak it with penetrating fluid the better so you don't have to get forceful with it.
Yes the screws can be a royal PITA to remove. Have a good sharp(ie clean) torx tool to use on them. I don't think there is one in the factory tool roll, yet some tool rolls will have the feeler gauge for checking the ABS gap(go figure). Be firm but don't break it off either.
I seem to remember the 1st time I did fork seals, when I pulled the forks I wasn't able to get the screws loose so I just disconnected the wire from the loom and left the sensor in the fork body while I worked on it. I have sense been able to get the screws loose and the sensor out, and back in. It can be done, with care.

Get all the surfaces good and clean, re-assemble and check the gap. If it is still wide, I'd then remove the skinniest shim and assemble, check gap... you get the idea.

In my case I was able to remove enough shim to get it to spec. I haven't had to buy any as yet. I do have the shims that I have removed if I ever need them for either bike.

[skidmore]

Got it, thx!

[rbm]

Page 5.18 of which manual? I mean, there is the PDF download here on motobrick of the factory manual but it is dated 1988 and mentions nothing about ABS. If you have an electronic version of the manual you're quoting, I would gladly accept a copy - if you offer, that is 

Official BMW service manuals for a select group of models are available at:
http://www.flyingbrick.de/board/filebase/index.php?page=Category&categoryID=3%7C
These downloads are sanctioned by BMW and have their blessing to redistribute.

I was referencing an early version of the K1100LT manual I have when I quoted the page number.  In the K1100LT/RS manual from the link above, the page is 34.11.  In that manual there are two front gaps specified:
Up to 1996 MY............................... 0.50 - 0.55 mm
From 1997 MY ............................... 0.45 - 0.55 mm

You'll note the gap specc closes on later model years.  Probably a good idea to keep the gap as small as practical because, being a passive VR sensor, the level of the signal degrades very quickly for very small changes in gap.

[skidmore]

Sweet, I will check out the link.

[enb54]

Official BMW service manuals for a select group of models are available at:
http://www.flyingbrick.de/board/filebase/index.php?page=Category&categoryID=3%7C
These downloads are sanctioned by BMW and have their blessing to redistribute.

Hi Robert, went to the page you quoted and got "You are not allowed to enter this page. You do not have the required permissions to enter this page." , do you have to create an account?

Eric

[rbm]

Probably Eric.  It's the German Flyingbrick site.  It's well worth opening an account just to access the goldmine of information that resides there.  You won't be disappointed, and no scams/spam.

[enb54]

Thanks Robert, registered and good to go now!