1 BMWK100 rear brake master cylinder issues Wed Nov 24, 2021 11:55 pm
Mike-the-bike
active member
Hi All
I hope someone can help with a very frustrating issue with the rear brake master cylinder.
Very Early 1983 BMWK100 13mm master cylinder
The rear brake caliper has had a service kit fitted and works fine, then I changed the brake hoses for stainless steel ones, again all working fine.
Then I noticed the rear master cylinder was leaking slightly, so I ordered a 13 mm refurb kit from Motobins UK (Insane cost for what you get).
Fortunately I had another brake master cylinder to play with to see how it all went together, mmmm simple, but this cylinder was pitted so cant be used.
I dismantled the working cylinder, cleaned it up and painted it, then carefully polished the inside to make sure it was not pitted, checked the new piston fit was good.
I have fitted the new seal kit to the 'working' master cylinder and fitted to the bike, but no matter how much I try I cannot bleed the system, there is no resistance to the pedal movement apart from the return spring.
I have even applied a vacuum to the bleed nipple on the caliper to see if I could purge the system that way.
I have disassembled and checked everything a couple of times and primed the whole system with fluid but still cannot get any brake pressure.
I am at a total loss, I rebuilt the front brakes no problem and done brakes on many other bikes but this has got me stumped...
HELP please
Any ideas?
Cheers
Mike
I hope someone can help with a very frustrating issue with the rear brake master cylinder.
Very Early 1983 BMWK100 13mm master cylinder
The rear brake caliper has had a service kit fitted and works fine, then I changed the brake hoses for stainless steel ones, again all working fine.
Then I noticed the rear master cylinder was leaking slightly, so I ordered a 13 mm refurb kit from Motobins UK (Insane cost for what you get).
Fortunately I had another brake master cylinder to play with to see how it all went together, mmmm simple, but this cylinder was pitted so cant be used.
I dismantled the working cylinder, cleaned it up and painted it, then carefully polished the inside to make sure it was not pitted, checked the new piston fit was good.
I have fitted the new seal kit to the 'working' master cylinder and fitted to the bike, but no matter how much I try I cannot bleed the system, there is no resistance to the pedal movement apart from the return spring.
I have even applied a vacuum to the bleed nipple on the caliper to see if I could purge the system that way.
I have disassembled and checked everything a couple of times and primed the whole system with fluid but still cannot get any brake pressure.
I am at a total loss, I rebuilt the front brakes no problem and done brakes on many other bikes but this has got me stumped...
HELP please
Any ideas?
Cheers
Mike