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Discussion Starter · #1 ·
Few days ago I got the red triangle and quick flashing of brake warning light on my dash but the brakes worked well. When I arrived home I did few checks and figured out it was my rear brake servo that would not come on when I depress the foot pedal. The red triangle would flash only when I depress the front brake lever harder (I guess when computer engages both front and rear as this bike has integrated braking).

Front brake and servo works well.

My rear braking power (without servo) is practically non-existent. The master cylinder tank is filled to correct level. I removed the fuel tank to access the ABS/Servo pack and checked the brake fluid level in each port. The front (higher one but towards the end of the bike) is nice and clean. The rear (lower and towards the front of the bike) is very dirty, dark brown colour.

When I depress the foot brake pedal I can hear a click somewhere, and when I depress it hard, I can hear the repeated clicking, as if a relay or something is being triggered but no servo motor and pump running. The brake light comes on when pedal is depressed.

Is my rear servo motor broken or something more serious?

Any tips or suggestions are welcome.
 

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2009 K1300S, 2017 S1000R & 2021 Vespa Primavera clown paint job
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You own a bike with a Servo assisted ABS unit . You can do a search on the subject but essentially your in trouble. Take a look at this system failure in many posts by doing a search. Make sure your sensor wiring has not failed front or back, see if there is metal chips on the rear sensor in the final drive hub. But please do some in depth reading on the forum about this. There are solutions ranging from a few hundred bucks to almost 3 grand. This problem is coming up more frequently as these bikes are "vintage" now. Read old. One has to change the brake fluid every two years in these bikes to keep the mechanics in the ABS unit in good condition. Occasionally the electronics fail. All in posts if you do advanced search for ABS failure.
 

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Discussion Starter · #3 ·
I'll try and wire the motors directly tomorrow to see if the rear motor is dead as it looks like it from troubleshooting so far. Has anyone tried replacing just the motor that powers the servo pump? I believe I've read somewhere people have replaced brushes on these motors. Are these motors alone available?
 

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2009 K1300S, 2017 S1000R & 2021 Vespa Primavera clown paint job
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One fellow found a ford fiesta car ABS unit that has the same motor. I believe the excentric needed some fooling with. Often it is just the brushes not touching the commutator. I bought on ebay one of the ABS units in question just to look at it. Lots of photos on a now dead forum unfortunately. Several people in the past have opened the motor side of the unit. I don't remember if it was a servo system or the vanilla ABS unit. Here is someones work. Also you can send it to
RH Electronics – Ihr Steuergeräteprofi \
they can repair it. There is also a bypass restore unit available.
 

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2005 K1200s 78,000+ miles going strong
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Just re-read your question on my PC and realised my original answer wasn't really relevant to you - hope you get it sorted !!
 

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Discussion Starter · #6 ·
I was not bale to wire the motor directly as it needs opening the box under the multi pin plug.

I have contacted Module Master and they are not receiving any BMW Motorcycle ABS modules for refurbishment until the end of the year as they are (reportedly) overwhelmed....

I would not mind looking at it myself to try and see if it is the motor brushes. Are the four steel brake lines the only thing that keep the module in place or there are other securing screws/bolts/clamps? I could see none.

I am also suspecting rear master cylinder as I am unable to get any braking power on the rear brake. The problem for bleeding the rear brake system is exacerbated without servo motor. I've read somewhere that the pressure that master cylinder creates also plays the role in the whole system, so if I cannot achieve sufficient hydraulic pressure that may be the problem in activating the servo motor.

Hey Beech, I was unable to access the photo album with the hyperlink on the pdf document. Would you have better link to the photographs? It is much easier working with photos than with text description alone.
 
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