K1200RS Front Brake Failure - Master Cylinder? - K-Bikes.com - Excellence in Motion
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post #1 of 7 (permalink) Old Sep 10th, 2008, 9:42 pm Thread Starter
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K1200RS Front Brake Failure - Master Cylinder?


Just bought a 2001 K1200RS with 8500 miles on it. A couple of days after buying it, I got the flashing ABS light and set out to fix the issue. I noticed that the bearing screw for the front brake lever was sticking out way too far, with the result that the cover plate would not fit on flush.

I was at first unable to screw the bearing screw (the screw that the brake lever pivots around) all the way in without causing the brake lever to bind. I then figured out the the brake was a tad bent from a minor lay-down the bike had had in its previous life. Bending it a little, it went into place and the screw was turned all the way in with no more binding.

In the process of messing with it, I turned the entire right side lever mechanism upside down, letting air into the brakes. Soon figured out that wasn't too smat, but figured no problem, I'll just bleed the front brakes.

Well I've bled them multiple times now and can't get pressure back into the brake lever, even after 40+ squeezes. I've removed both calipers, forced the pistons open and pinned them there, and cycled from left to brake control module to right caliper repeatedly. What seem to happen is that I'll get either the right or left caliper alternately unwilling to release any fluid into my speed bleeder. I've scanned the brake lines in detail and cannot find a leak, nor do I suspect one since the brakes were working before my interference.

I am now speculating that I've somehow screwed up the plunger arrangement in the front brake master cylinder by bending that lever. However, I can't find any information online about the detail of that master cylinder. I did just order a Clymer manual in case that helps.

By the way, I did find that the ABS sensor gap was way too large up front, and am hoping that will fix my ABS problem. Right now my priority is just getting the front brakes back!

Any thoughts would be appreciated. I want to ride this weekend!
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post #2 of 7 (permalink) Old Sep 11th, 2008, 10:26 pm
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Bleeding problems

One of the challenges in bleeding the brakes on a motorcycle is that the output port of the master cylinder is higher than the vent port when the bike is on the center stand. Put your master cylinder cover back on, put the bike on the side stand, turn the bars full lock left and slowly pump the lever a few times. You'll probably find the brakes return to normal. Whether they do or not, leave the bike parked that way for awhile. This allows any trapped air to rise through the sytem and through the vent port.
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post #3 of 7 (permalink) Old Sep 12th, 2008, 9:08 pm Thread Starter
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Thanks. I did that tonight, and it may have been what helped me get fluid through at all 3 locations: front left, front right, and the control module under the seat. However, I still can't get pressure at the brake lever, even after 60+ squeezed.

Am wondering if the 30mm barbacks put undue stress on the brake line, though I don't see any fluid and I did have pressure pushing fluid out when using the lever. My other thought is whether my having the caliper pistons held open by a block of wood could have any impact. Any ideas much appreciated.
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post #4 of 7 (permalink) Old Sep 13th, 2008, 1:51 pm Thread Starter
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Found problem

Hallelujah - after going through a whole bottle of brake fluid, found a pinpoint leak in one of the lower brake lines. Dunno why I didn't see it before - idiot I guess. Thank you all for the help.
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post #5 of 7 (permalink) Old Sep 21st, 2008, 9:18 pm
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my experience

Originally Posted by Carguy
Hallelujah - after going through a whole bottle of brake fluid, found a pinpoint leak in one of the lower brake lines. Dunno why I didn't see it before - idiot I guess. Thank you all for the help.
I would suggest replacing all of you brake lines at the same time with the Speiglers. I made the mistake of doing one line, then another started spuing. Only then did I spend the money for the ss lines.
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post #6 of 7 (permalink) Old Nov 30th, 2008, 1:32 pm Thread Starter
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Check out the master cylinder adjuster screw

After more bleeding and trying various things, I'm getting good brake pressure, but the lever comes almost to the handlebar to get it. The fix for this seems to be adjusting the master cylinder screw inside the lever housing. You have to heat it up to soften the loctite (see similar thread - search for red loctite). Also, the Clymer repair manual describes this adjustment procedure.
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post #7 of 7 (permalink) Old Dec 2nd, 2008, 7:40 am
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If you turn the master cyl. upside down again (I did once) - you can get the air out by just slackening the banjo connector at the master cylinder, use it like a manual bleeder, squeeze the lever and push fluid through, tighten the banjo and release the lever.

Be careful to catch the fluid and not get it on paintwork. I only do this with plastics off, everything wetted and the front fender covered.

In fact I've found using the banjo as a top bleeder, also slight tapping with a rubber hammer on the master cyl, sometimes removes the spongyness caused by trapped air still left at the top after you've bled and bled.

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