BMW K bikes (Bricks)

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timz10000

timz10000
Silver member
Silver member
On a recent ride, my 1985 K100 rear brake fluid drained out. Advice on how to troubleshoot / fix?

I notice that the boot on the master cylinder has disintegrated (pic). I'm also curious that there's a second nipple on the reservoir - is that supposed to be like that, or does that connect to something? (See pic). 

I see you can buy a Rebuild Kit  like this - is that what I should get? 

I also have a 1985 parts bike that was sitting in a barn for years, assuming this is something I shouldn't fix with parts from that since rubber is a key component of this.

Any advice welcome.Troubleshooting rear brakes drained of fluid Img_2012
Troubleshooting rear brakes drained of fluid Img_2011


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1985 K100
    

duck

duck
Life time member
Life time member
Take it apart and inspect/clean it before spending any money.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/master.leak/master.leak.htm


The second nipple on the reservoir is supposed to be capped like yours is.  I have no idea why it's there.


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Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

Laitch

Laitch
Life time member
Life time member
Yours looks to me that the unused port has lost its cap. Here's an image from Euro Motoelectric of a similar reservoir with its right-side port capped.
Troubleshooting rear brakes drained of fluid Screen43


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1995 K75 77,000 miles
Troubleshooting rear brakes drained of fluid Usa-lo10
    

MartinW

MartinW
Life time member
Life time member
Once you get the master cylinder up and running fill the rubber boot with heavy silicone grease. The grease helps stop the boot from degrading, and stops the ingress of water and road crap. In OZ I can get spare boots $4.00 AU from a local shop that specializes in sleeving brake cylinders and calipers.
Regards Martin.


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K75s Hybrid
    

Dai

Dai
Life time member
Life time member
Laitch is right. A bleed nipple cap will do the job just as well as (a) there's no pressure in the reservoir (b) the material the cap is made of is designed to cope with hydraulic fluid.


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'83 K100 upgraded to K100RS spec, '87 K100RT
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California
    

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