Front Brake Drip - K-Bikes.com - Excellence in Motion
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post #1 of 23 (permalink) Old Mar 16th, 2014, 11:59 am Thread Starter
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Front Brake Drip

My K75 has been hibernating peacefully in the shed, as usual in winter. Three weeks ago I noticed a drop of liquid on the storage pocket lid right side. It was brake fluid, had dripped from where the handle operated plunger goes in and out. Next day one more drop. Since then two more drops.
I havent' been using the brake. Maintenance on the front last year was changing the pads and changing the fluid. Both operations went well. I rode a couple of hundred miles after bleeding and changing the fluid, before putting the bike away.
I'm thinking I should have a professional wrench diagnose and fix whatever is going on here. Meantime, do any of you folks have an educated guess as to what could cause the front brake brake to spontaneously drip like this?
In the last week there has been no drip. But if I look in at the plunger and work the brake lever, I can see wetness in that area. The master cylinder has not noticeably lost any fluid.
Thanks,
Steve
1990 K75RT
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post #2 of 23 (permalink) Old Mar 16th, 2014, 12:33 pm
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The seal on the piston is failing. You need to get the master cylinder overhauled or replaced. It's costlier to replace, and I've had mixed results with overhauling. Protect your paint from the brake fluid.

Frank

'17 R1200RS, 2 yrs. 25,000 mi.
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post #3 of 23 (permalink) Old Mar 16th, 2014, 2:14 pm Thread Starter
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Thanks, Frank. Yes, I've got those heavy-duty blue shop towels covering the drip area.
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post #4 of 23 (permalink) Old Mar 16th, 2014, 6:18 pm
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Before you run out replacing parts, it's a good idea to take it apart and inspect it. Many times it's just dried brake fluid (a.k.a. crud) that has built up over the years which is making the seals leak.

Remove the set screw that holds the piston in the master cylinder. Clean and inspect the seals on the piston for issues. Clean out the bore with some 0000 grade steel wool and inspect it for pitting. If it's not pitted and the seals still look good, then re-install it and see if it still leaks.
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post #5 of 23 (permalink) Old Mar 16th, 2014, 6:44 pm Thread Starter
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Quote:
Originally Posted by FlyingDuck
Before you run out replacing parts, it's a good idea to take it apart and inspect it. Many times it's just dried brake fluid (a.k.a. crud) that has built up over the years which is making the seals leak.

Remove the set screw that holds the piston in the master cylinder. Clean and inspect the seals on the piston for issues. Clean out the bore with some 0000 grade steel wool and inspect it for pitting. If it's not pitted and the seals still look good, then re-install it and see if it still leaks.
Thanks--will do, Drake.
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post #6 of 23 (permalink) Old Mar 17th, 2014, 12:00 am
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The K75 ain't got a set screw to hold the piston, it's circlip in the outer end of the bore.
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post #7 of 23 (permalink) Old Mar 17th, 2014, 7:45 am
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Quote:
Originally Posted by IngeK
The K75 ain't got a set screw to hold the piston, it's circlip in the outer end of the bore.
Yup.
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post #8 of 23 (permalink) Old Mar 17th, 2014, 6:06 pm
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My suggestion is buy this:



On page 428 you will find:






I haven't rebuilt the front master cylinder on a K bike, but I did my Triumph Tiger successfully. It wasn't that hard. I cannot confirm the above diagram is accurate. Clymer has a few diagrams and photos that look nothing like my bike, but master cylinders I have seen were all fairly similar.

My first thought would be that part 11 has worn so that it is no longer making a tight seal.

Get the manual. Read the section on disassembling and reassembling the front master cylinder. Then decide if you want to try it or let someone else.

Beemerboneyard sells rebuild kits at $50 for nonABS and $70 for ABS

Last edited by 97tiger885; Mar 17th, 2014 at 6:24 pm.
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post #9 of 23 (permalink) Old Mar 17th, 2014, 6:37 pm Thread Starter
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97tiger: Yes, I'm looking at that diagram in my Clymer's. Good. Thanks guys, you have all given me a road map to get to where I need to go. First thing to do will be to remove the master and disassemble, clean and inspect. And take it from there. I'll let you know how it turns out
Steve
1990 K75RT
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post #10 of 23 (permalink) Old Mar 17th, 2014, 10:08 pm
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Quote:
Originally Posted by stevemac829
97tiger: Yes, I'm looking at that diagram in my Clymer's. Good. Thanks guys, you have all given me a road map to get to where I need to go. First thing to do will be to remove the master and disassemble, clean and inspect. And take it from there. I'll let you know how it turns out
Steve
1990 K75RT
Part 11 is listed as an assembly. That means it probably is several parts including a spring, a piston, a rubber o-ring and more. Take care in removing everything. Note the order in which it came out and its orientation.





This is what came out of my Tiger. It looks as if the K internals may be less complicated, but be prepared. The part I have labeled as 9, the piston, is not symmetrical. I put it in wrong the first time and the brake did not function.

Per FlyingDuck's suggestion of cleaning and reinstalling: if you have no plans to die soon, you plan to keep the mc for a while, and your budget allows, I would buy the rebuild kit. Unless you enjoy fiddling, it is one and done for the next 25 years.

Last edited by 97tiger885; Mar 18th, 2014 at 2:27 pm.
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