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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Lucky_Ted on July 08, 2018, 03:49:09 PM
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Have a 1987 k75c non ABS that spent about 10 years sitting. Im pretty much done with the restoration except for this sticking point. The front brake lines were bled before being stored. I put some new fluid in the master cylinder but no fluid is reaching to the bleed nipple. On top of this I cant pump the brakes as the trigger for the master cylinder is "floppy" (no tension, trigger stays at whatever position its left in).
Unknown whether this could be caused by a blockage in the empty lines, a cable is broken, or if I should grab a whole new master cylinder. Any input here would be greatly appreciated.
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Brake fluid overtime can crystallize. First thing would be to pull apart the master cylinder clean the piston and cups carefully with clean brake fluid. Then clean and inspect the master cylinder bore for scores and pits. Also check that the small hole in the bottom of the reservoir is clear. If there are no scores and pits in the bore and no marks on the edges of the cups it is sometimes possible to get the master cylinder to work again. Mild scoring and pitting can sometimes be honed out and a new cylinder repair kit fitted. Major scoring and pitting can either be resolved by finding a good second hand one or by having the cylinder sleeved and a new piston made which costs $200.00 Au in OZ.
Regards Martin.
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yup, what he said, Hopefully master cylinder just needs cleaned, new ones can be pricey.
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As a matter of course it would be prudent to replace the brake lines. I've had a OEM brake line delaminate internally. An internal flap of rubber over a hole made a one way valve allowing it to suck in air but not leak fluid. I had a hell of a time trying to bleed the brakes. I eventually worked out what was going on.
Regards Martin.
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Have you attempted a vacuum bleed?
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I am not sure a vacuum bleed is the best way to go on these bikes.
I say that as a former fan of that technique. I quit doing it when I found the vacuum was pulling air into the system past the seals in the front master cylinder of my 16V K100RS. I spent an entire afternoon and nearly a quart of fluid trying to get the air out of the system so I could get a firm lever feel. Conventional squeeze and bleed had it working in 10 minutes.
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I am not sure a vacuum bleed is the best way to go on these bikes.
I say that as a former fan of that technique. I quit doing it when I found the vacuum was pulling air into the system past the seals in the front master cylinder of my 16V K100RS. I spent an entire afternoon and nearly a quart of fluid trying to get the air out of the system so I could get a firm lever feel. Conventional squeeze and bleed had it working in 10 minutes.
Interesting, I always use my vacuum bleeder and have never run into that situation.
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I use the conventional method and find it works fine, though I do need to run three of four reservoirs of fluid through the system. I always start at the ABS and then the LHS then the RHS and lastly tie the lever back overnight, had worked well for me so far.