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Discussion Starter #1
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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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
 

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PsyKotic Waterfowl
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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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Discussion Starter #5
FlyingDuck said:
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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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
 

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Discussion Starter #9
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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stevemac829 said:
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.
 

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Discussion Starter #11
Well, I have the front master off and on the workbench. Also the rebuild kit. Looks like I'm going to need a good pair of circlip pliers, the circlip retaining the piston is really in there. Any recommendations of a brand or type or store that would sell pliers that could do this job?
Thanks, Steve
 

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stevemac829 said:
Well, I have the front master off and on the workbench. Also the rebuild kit. Looks like I'm going to need a good pair of circlip pliers, the circlip retaining the piston is really in there. Any recommendations of a brand or type or store that would sell pliers that could do this job?
Thanks, Steve
I would think Harbor Freight, any auto parts store and probaby big box hardware stores.

I took an old needle nose pliers and ground the tips down to use on the Tiger. It did the job. Not as good as a dedicated pliers, but good enough.
 

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stevemac829 said:
Thanks, Frank. Yes, I've got those heavy-duty blue shop towels covering the drip area.
Wash it off with water and don't allow it to spread by wiping with a shop towel. It only gets worse.
 

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stokester said:
Wash it off with water and don't allow it to spread by wiping with a shop towel. It only gets worse.
Buy the cheapest bag of nonclumping cat litter you can find. This is great stuff for gas, oil, coolant, hydraulic fluid, etc. Cover the spill. Let the litter soak it up. Sweep into a dustpan, put into a plastic bag, done.

That doesnt help with the gas tank, etc., but great for floors.
 

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Discussion Starter #15
The bore looks good. Ready to put the mc back together. One odd thing tho: there are two parts included in the rebuild kit that I didn't see when disassembling. They are a rubber washer and a large flat metal washer (see pic). In the kit they were slipped onto the business end of the piston, I think just as a handy way of packaging them. Any suggestions as to where they might go?
thanks,
Steve
1990 K75RT
 

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Discussion Starter #17
IngeK: yes , that's exactly how it came packaged.Is the rubber piece supposed to stay on the piston? And the metal washer? That won't fit in the bore.
On the outside of the bore opening?
Like I say, neither piece was to be seen on my old master.
Steve
 

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Discussion Starter #19
Thanks, Inge. The throttle housing, took it off and there they are. It wasn't clear to me what (if anything) I was supposed to do with that. Sorry if I seem kind of dumb about this job. Never touched the master before except to bleed fluid.
Sure is dirty inside the throttle housing.
Steve
1990K75RT
 

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Discussion Starter #20
The master is finally back on , brake is good. Took a while I've been so busy with other (non-motorcycle) things. Thanks to all who helped me. The rebuild kit did not include the piston circlip or the o-ring for the reservoir, but I picked up these items at the dealer. Took a while to get the air out of the system (non-abs), but it works fine now and the bike passed State inspection the other day.
I am having some trouble getting the throttle adjusted at the grip.It appears to be a straightforward job--slide the grip's teeth under the throttle wheel so that there is no tension on the cable, screw it down. It FEELS good--that is, the grip 'snaps' shut when I release it, but somehow the throttle is not closing all the way. Engine is running at 1500 rpm at hot idle--it had been around 900 for years with only occasional adjustment of the idle screw.
I'm wondering if I need to back that screw all the way off, then re-assemble the throttle grip assembly and take it from there? Any help appreciated.
Thanks,
Steve
1990 K75RT
 
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