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Discussion Starter · #1 ·
Bike is an '02 RS integral ABS, 58kmi.

TLDR: If anyone can point me to a rear ABS troubleshooting thread I will happily start there.

Otherwise, bike has been stored outside all summer under a waterproof cover, battery on trickle charger. Now with Fall riding season here, I was prepping to ride and found the rear brake servo does not activate when pressing the pedal. When I depress the brake pedal, key on but not running, I can hear a faint relay click near the battery. Fluid was flushed no more that 2 years ago and only has a few hundred miles on it. Battery is 13v, rear brake light replaced today and functions properly. It passes the startup brake system self test and the roll away test. Front brake lever activates the front servo and brake light normally. When I pull the front brake lever hard enough to activate the rears, the servo sound changes the way it always has, like it's under a load, and then the brake fail light starts flashing.

It seems like I've done the easy stuff. Nearest dealer is probably 200 miles away, but not sure if a GS911 is something the local lesser bike repair places would have, and would it even be helpful.

Suggestions on what to try next?
 

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2005 K1200S
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Mine was giving me problems after being serviced by the dealer before I acquired it (long story). The servo motor was running continuously and quickly drained the battery. I just decided it would be better to just dump it now rather than fixing and still have failures in the future. I split the cost with the previous owner/friend so I went with the RH unit. The RH unit is very well made and has the electronics with it. You can go the other route and remove your electronics from your servo unit. Removing that unit is not an easy task. Its really tucked in there and is mounted on a plastic tray which makes it a pain to remove because I didn't see any way to remove the three screws on the bottom of the tray holding the servo.
Motor vehicle Automotive design Automotive exterior Auto part Automotive super charger part


Here is the unit removed
Automotive tire Input device Peripheral Motor vehicle Automotive lighting


Here is the RH unit mounted on the plastic tray
Hand Automotive tire Tire Finger Bumper

And the RH unit installed
Motor vehicle Automotive design Automotive exterior Automotive exhaust Carbon

My front brakes worked great, however the back not so good. The rear uses a 16mm master cylinder. By switching to a 13mm Brembo which can be bought new for around $52 increased the stopping power of the rear considerably.
Tire Wheel Fuel tank Automotive lighting Vehicle
 

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K1300GT SE / GSX1400 / LRD4
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So is the RH unit just a blanking plate with some smarts to fool the ecu that abs is still present?

Re 16mm vs 13mm rear brake master cylinder, is this the same for the later K1300GT? The max bmw parts fiche does not list item #3. Would be a good upgrade imho.

Love your workshop btw
 

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2005 K1200S
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The RH unit is complete with the electronics which allows operation of the speedometer, at least on my model year and does fool the ECU I guess. The unit is very well machined with bypass ports. Not sure who makes the other option which is just a stamped out piece of steel and tubing and ports to connect your lines. It has a blanking plate you use to connect you original electronics after you remove them form your unit. Do a search on servo problems and it will probably come up. If you go with the RH make sure you get the correct model. There is one for analog or Can.
 

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K1300GT SE / GSX1400 / LRD4
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Cheers, thanks for the link, it answers my question:
"THE CONVERSION KIT TO REPLACE THE FAULT-PRONE BMW ABS 3
The conversion kit for the fault-prone BMW ABS III and ABS II. Available in five variants, for BMW motorbikes built between 2000 and 2006. The device replaces the standard ABS 3 of the manufacturer FTE and is instead installed in the motorcycle. It hydraulically connects the control circuits with the brake circuits, thus the brake system operates as conventional without ABS system."

Mines a 2009 built K1300GT, so I understand this kit is not needed for my bike, not to say the 09 ABS is less prone to issues...but touch wood nothing yet...

The rear master cylinder size may be worth a look, rear brake performance is a bit lacklustre, but as it's linked, may not be smart to increase line pressure by going to a 13mm master may upset the balance. Hmm, food for thought....
 

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Discussion Starter · #8 ·
Does the ABS warning light go off normally?
Does the rear pedal activate the tail/brake light?
Several ABS threads here with basic search. Most don't end well.
The warning lights give no indication of a problem until I activate either the pedal or hand lever. When activating the foot pedal, the general fail light comes on solid and the ABS light starts flashing 4 hz within a second or two of pressing the pedal. Both go out when the pedal is released. When using the hand lever, after a few seconds the general light comes on solid and the ABS fail light flashes 4 Hz and they stay on even after the hand lever is released until switching off the engine. This seems to agree with the chart in the Clymer.
The rear pedal does activate the correct filament in the brake light. The brakes pass both the startup self test and the roll off test. Conversely, if I hold down the foot brake first and then turn on the key, it (correctly) fails the startup self test.
 

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Without checking for trouble codes the shade tree mechanic assessment would be that If the abs passes the roll off test it would seem to indicate that the servo motors, brake light circuit, brake switches and fluid level sensors pass the self test. Since a problem is indicated upon application of braking it would seem to indicate either a leak, or, a pressure transducer problem in the unit. But that's just a guess without knowing codes.
 

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2005 K1200S
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What ever the problem may be with the unit you still have something that is overly complicated and prone to fail. Bottom line your going to spend a ton of cash to keep that unit in place. In my case I didn't get any codes that told me the explicit problem with the servo unit other than the brake failure itself. It may be wise to get a code reader and check for any codes. Your problem is different from mine as my servo motor ran as soon as you turned the key and the the general fail light came on with ABS flashing 4 HZ. I had front brakes but no rear at all. All fluids were full. I could have pulled the unit and fiddled with it but in the end its still prone to fail.
 

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Yep, Servo ABS is the dumbest thing ever put on a motorcycle. So complex some of the best ABS overhaul outfits in the US and Europe have been unable to repair it. When you consider they can rebuild ABS units on expensive BMW cars and Ferraris, that's saying something.
 

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Discussion Starter · #12 ·
What ever the problem may be with the unit you still have something that is overly complicated and prone to fail. Bottom line your going to spend a ton of cash to keep that unit in place. In my case I didn't get any codes that told me the explicit problem with the servo unit other than the brake failure itself. It may be wise to get a code reader and check for any codes. Your problem is different from mine as my servo motor ran as soon as you turned the key and the the general fail light came on with ABS flashing 4 HZ. I had front brakes but no rear at all. All fluids were full. I could have pulled the unit and fiddled with it but in the end its still prone to fail.
Going to dig into it this weekend and see what I can see. The RH unit does look interesting, thanks for the heads up on that. Does it still allow use of cruise control?
 

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Discussion Starter · #13 ·
Without checking for trouble codes the shade tree mechanic assessment would be that If the abs passes the roll off test it would seem to indicate that the servo motors, brake light circuit, brake switches and fluid level sensors pass the self test. Since a problem is indicated upon application of braking it would seem to indicate either a leak, or, a pressure transducer problem in the unit. But that's just a guess without knowing codes.
That's what i was thinking. Was just hoping there was something obvious I maybe missed. On another note, sort of: How do you like those Italian brake hoses?
 

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No problems with the FrenTubo lines. Initially they sent the wrong front lines but the exchange was painless. I could've used the first pair but would've had bend the banjos a little more. The shipping from Europe was a lot quicker than I was expecting.
 
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