ABS Problem - 1992 K75RT

[skidmore]

I did a google and found the usual reset procedures and fault code deciphering. Neither fit my dilemma. This is weird, me thinks.

Long story short, first, then all the gory details. Simply put: my ABS light came on whilst tooling down the slab AND my front brake lever was rock hard. Rock. Hard. Well, it had maybe 1/8" - 1/4" play/slop when I pulled on it but then it came to a stop, rock solid. When I release it, it returned to its normal position.

So, I'm tooling down the interstate on my way to go look at a 92 K100RS (yay!) that was for sale. About 40 miles into the trip I noticed my ABS light was lit up solid. The "real" ABS light in the speedo cluster, not the triangular "hazard" light above the neutral light. What are the odds! I'm on way to look at a 4 valve 4 banger in my favorite color (1992 blue!). Oddly enough the seller had stated his ABS was inoperable LOL! Anyway, ABS light glowing solid and I'm all WTF. After 5 or 10 seconds of digesting indication of bad news I had the wild idea of touching my brakes to see if they worked. The ABS light aglow reminded me of the typical car when the brake pedal travels too far and the brake light comes on. I pulled gently on my front brake, and as described above, the lever moved <1/4" and then became hard as a rock, as if it had come up against a steel curtain. The front brakes did not respond. I tried the rear brake and it responded normally. Ho-lee-chit I thought. I could be killed!

I safely pulled to the shoulder, called the guy with the RS and shared my woes. All this time the ABS light remained lit up. After I finished talking to the guy I shut off the engine hoping a "power cycle/reboot" would fix things just like with Microsoft Windows. No luck. The ABS and hazard lights behaved normally, as in flashing in alternate fashion. I always tap both brakes before I roll away, and did so that time, and they flashed in unison. As I pulled away they remained flashing in unison for a couple seconds or so, then the hazard light went out but the ABS light remained lit. Boy oh boy, talk about a putt buckering 50 mile drive I was embarking on with only a back brake. I touched the front brake lever and it behaved same as before.

A couple miles down the road the ABS light went out! I let my elation subside before trying the front brake. It responded normally! Happy! Confused! Concerned? Should I make a u-turn and resume my trip to check out the bike? LOL! Not so fast! Suddenly both lights lit up, flashing in unison a several times before the hazard light went out and the ABS light remained lit. 5 or 10 seconds later the ABS light went out. Front brake check: success! Back brake: check (which was never an issue, but I had to make sure).

The ABS light remained out the rest of the ride home. I stopped at a rest area to clean my britches out  :hehehe  and tried to soak up the whole fiasco. I've read all about the faults and resets yadda yadda yadda and would be ok accepting the ABS system had finally taken a shit after 20+ years and 80K miles. But the real stumper is the behavior of my brake lever. Why was it rock hard and inoperable? That, motobrickers, is the $64,000 question.

[Zipster]

As I own a 1996 K1100LT I've become well used to the ABS2 system and so I'm not so familiar with the earlier ABS1 system which I believe you have. I'd be doing a service on my front calipers and then on my front master cylinder including a service kit and finally replacing the brake fluid before carrying out a reset on the ABS. The rock hard brake sounds like an obstruction of some sort.

[Elipten]

And that is exactly why I did not buy that wack crap ABS system on my bike in 1990, and will not buy a used BMW with.  My 2014 Honda has a system a far more improved than the old BMW system, but to be expected 25 years later.

[skidmore]

Obstruction, right. It felt as if the piston(s) was/were binding or coming up against an obstruction. But, why did it correlate only with the ABS light being lit up? That's what has me puzzled. And bummed out. Worth noting is never at any time did the front wheel feels as if the calipers were squishing on the discs.

Hell, if a component is gonna take a dump and relegate the system inoperable, I'm OK with that. I'd rather it NOT take a dump if I had my druthers but if it does and my brakes function otherwise, I will be just fine. In fact, it will be the excuse I need to jerk the entire system and pick up a 25lb weight loss  :riding:

[Scott_]

Sounds to me like you are having a problem with the modulator.

http://www.motobrick.com/index.php?topic=538.0

[skidmore]

Is modulator malfunction indicated by the ABS lighting up solid? I couldn't find anything regarding a solid-on condition.

I tried to imagine how and if the modulator was the crux of the problem. Or is it the ABS ECU with the *intermittent* problem? The modulator behaves how the ECU tells it to behave, right?

On the ride home I figured it would behoove me to verify and clean all electrical connections in the ABS system. (The entire bike, for that matter)

[Zipster]

You may get some answers here - http://forums.bmwmoa.org/showthread.php?64276-1992-K75S-ABS-light-constantly-on

[Jumpin Jimmy B]

 I experienced something similar about 3 year's ago.

Over winter I had the wheels powder coated gloss black.  I also did the axle spacers. Upon reassembly all seemed OK. But with 10 minutes on the first ride when coming to a stop sign the front brake lever was very hard to pull. It felt hard but the bike was NOT slowing down!?!?! WTF !!!!??! So I pulled real hard and quick while also on the back brake and got the bike stopped.
 Being brave/stupid, I allowed for more stopping distance and kept riding trying to figure it out. During all of this there was no ABS light. It's a 93 K1100 RS by the way.  So for two weeks I keep riding.
If I use the front brake to stop it cannot be just to slow down, you have to stop like you really mean it. Finally the ABS light goes on & stays on. Oh great, more fun I figure. So I make up an LED light & wire to read the codes from that lone plug hanging near the battery box. The information on how to do this is in one of those links or on the tech notes in this site. I forget the code number, but it was reading a front wheel ABS sensor fault.
  So I ponder that. remember the powder coating? And then anal retentive me wanting the axle spacers to match? Sure shootin, once I adjusted the space from the sensor to the ring, by removing one of the .012" spacers and reset the system, all was well and the brake lever and stopping action was PERFECT!
  I also bleed the system annually and change the front AND back brake fluid out. Also changed out the brake lines for a black coated stainless set since then.

 So, just for grins, check the spacing on  the front ABS sensor, then change out the fluid and finally inspect and possibly change at least the front lines out.

 Also, your battery is good right?

 Good luck!

 

[Motorhobo]

Never heard of ABS actually affecting braking such that it would be result in hard lever.  I'm wondering whether the hard lever is the problem and the ABS light is just a symptom...

When did you last replace brake lines? Old lines can cause blockage due to shedding of rubber flakes on inner hose lines. I don't know why that would result in an ABS fault, though. But if your lines are very old I'd replace them -- more dangerous than a faulty ABS unit. Such a blockage due to a tiny flake of rubber could cause a temporary blockage, then dislodge, then reseat itself In a blocking position at any time. Not good.

I've had ABS I for over 100k miles more or less problem-free so I don't agree with Elipten's assessment. Much rather be with than without...ABS I works -- might be old tech but it does prevent the lockup as designed.

Btw I have had my ABS 'fix itself' before. Is it possible that you got some debris stuck in the caliper that then dislodged itself?

[Elipten]

I completely agree in having ABS.  I have it on my newest Honda.  I just felt when buying my BMW in 1990 the technology on the BMW was crude and not advanced.  I wanted it and was leaning to buying it but the dealer and tech told me their experiences were not great so I did not buy.  When I hear about these problems and difficulty in parts and service, glad I did not buy. 

I don't care how fast the vehicle goes, but I sure want it to stop reliably.  I wish my K75 had stronger brakes.  I expect brakes to work when I pull the lever.  These types of malfunctions resulting in loss of brake function while riding are unacceptable.

[skidmore]

Thanks Zipster. I am anxious to read the link.

Jimmy B: it is an eerie feeling to tug on the brake lever and get nada. Even though I was 45 -50 miles from home via interstate, I had no choice but to ride'r on back to the ranch. I felt comfortable relying on the back brake. Not optimal, but doable. Today I am going to comb the whole system.

I haven't replaced any brake lines, ever, Motohobo. I have owned the bike just less than 2 years. Hopefully I can identify the root cause without having to replace hoses in a process of elimination sort of fashion (if that makes sense).

[skidmore]

You may get some answers here - http://forums.bmwmoa.org/showthread.php?64276-1992-K75S-ABS-light-constantly-on

Thanks for posting this, Zipster. I didn't come across it in my search last night. It seemed like I poured over many sites, many of which repeated the same info. I never found one link with "solid on" info. I have a couple gallons of gas in my tank to burn off before I pull it and commence work. Sounds like it would behoove me to get an LED from The Shack and determine the fault code.

In the event I experience this problem in the future (regardless of outcome of my pending troubleshooting efforts), could I simply jerk the connector from the ABS ECU behind my seat, shut off the engine and restart, and ultimately end up with a nonfunctional ABS system BUT a functional brake system?

[Zipster]

You'll probably need to pull a relay as well to put out the dash lights.

[skidmore]

Cool, thanks.

[Motorhobo]

If you have had the bike for two years and don't know the service record of the brake lines before then, do yourself and any dependents you have a favor and replace the brake lines first order of business.

Friend of mine -- 1999 R1150 -- 2012 -- brakes locked in a turn due to internal hose shed -- boom, lucky to be alive.

[Elipten]

+1. On most bikes they are original.  People do not know to replace every 5 years or too cheap.

You must have reliable good brakes and ties.  Your best defense.

[skidmore]

I have been too busy - and maybe lazy a bit too? - to commence troubleshooting. Saturday's weather was forecast to be better than Sunday's and since I was anxious to ride as well as see if the fault would recur, I rode Saturday. No problems the first 100 miles of 40mph cruising around the back roads. This time though I had front brakes. The light came on solid for a bit, flashed a bit, went out a time or two and eventually stayed lit up. I figured I would troubleshoot on Sunday. My local Radio Shack is closed on Sundays thus no 12v LED for crafting a diag light. Monday I picked up three of them at 30 cents each! RS is closing down. The LEDs were one of the items marked 90% off. Perhaps in the next day or so I will muster up the gumption to brave the chilly garage air and start sorting things out.

[enb54]

Have not replaced my brake lines yet (about 90,000Km or 54,00 miles) but this thread has convinced me that it is time. Certainly don't want to have a failure, and the machine is a '91...

[skidmore]

I finally fired up my LED and deciphered the fault. 3 blips = front wheel sensor. I suppose that is about as cheap of a problem as I could hope for - but I haven't priced a sensor yet. Surely can't be higher than a $195 modulator or the $500 brain box. I have yet to verify the sensor's connector. Maybe it needs cleaned up and I will be on my way.

[johnny]

greetings...

since the lights came on tooling down the freeway... im thinking i would try the reset a few times before doing anything...

i jumped a bump and my abs lights came on... the front and rear wernt spinning the same so i got a fault... it took me 6 months to get it to clear... one day i reset it 300 times... was gonna call it quits and on the 301st reset it took and was good from that point on...

on another moto my tior rubbed to abs wire and my abs lights came on... after replacing the sensor it took about 20 resets for it to take...

you may have a gap or sensor wire problem... or you may just need a reset...

j o

[skidmore]

300?  :hehehe good thing you had patience to give it a go one more time 

I reckon I will monkey with the connector and verify the wire has no breaks etc.

I realize how important the gap is. Is there really a possibility it has gotten out of whack? The mounting bracket seems to be a rather solid not-too-compromisable of an arrangement. I reckon I will verify gap too though.

Let's assume I was to buy a new sensor (not gonna happen, but play along...). After installation, does a reset need to be performed to clear the fault? I reckon so but it doesn't seem too ridiculous to ask.

[johnny]

my experience is once the abs faults it must be cleared to work again...

whats whack is after each reset you gotts to ride a few feet to make sure it clears...

j o

[Motorhobo]

It is definitely possible that the gap is the culprit. Read this thread...before you do anything else, follow the procedure to allow the wheel to self-center.

http://www.motobrick.com/index.php/topic,5252.msg32535.html#msg32535

  If that doesn't help then you might have to look more closely at the sensor...but that sensor is a PITA to get off the caliper...it's got a Torx nut instead of a regular hex...can't use a Torx socket either or even a Torx socket on a 1/4 drive screwdriver...you need a Torx screwdriver. So if you're planning on dealing with an ABS sensor issue, do it in conjunction with your brake hose replacement while you have the calipers off the bike and on the bench. Also, consider getting the caliper rebuild kit and doing the whole shebang. Brakes aren't something you want to do piecemeal because bleeding is such a pain on the arse and you want to do that as few times as possible. Take a day, do it all once and have peace of mind for years.

Btw, there are also shims between the sensor and the caliper that determine the sensor gap, but I don't believe that's your problem. The gap isn't variable at that point without installing or removing shims, so if it ever worked then the system at that point is unchanged and is still within tolerance. You should be looking for what elements of the system that have changed, and I'd think the most likely suspect would be something as simple as the wheel alignment.

[Motorhobo]

my experience is once the abs faults it must be cleared to work again...

whats whack is after each reset you gotts to ride a few feet to make sure it clears...

j o

You also have to ride it more than just a few mph after a reset to reboot the system. Last week I reset, rode it a few mph around the cul de sac, but no joy. Did that a few times...figured it's hosed...gave up...rode off down the road and as soon as I got to 30 mph the flashing fault light went out. There was great rejoicing, but also self-dumbass-calling because I wasted time on multiple resets when i really probably only needed one followed by a good ride.

[skidmore]

I did the "wheel re-seat" procedure, FWIW.

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.

Next I tried the reset procedure. I wasn't sure if the ABS button was to be pressed BEFORE turning on the ignition. To be safe I pressed in beforehand. I held it for a 30 count and turned off the ignition while continuing to press the button.

The initial roll away didn't trigger the ABS light to go out. Damn  :dunno . As I rode along, I pressed the ABS button expecting the flashing to stop and remain lit up solid. No go. It is as if my ABS button isn't  functional? And if it isn't, then my attempt at the reset procedure was for naught.

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