K11 Owners Group

[Tootles]

Hi Guys,
Sorry, not been around for a while. Had a summer of discontent revolving around (and around) the front brakes.
Take the front wheel off, put it back on. Right hand caliper binding. Strip everything down, re-assemble, bleed brakes, right hand front caliper binding. Twenty miles of 'light' rubbing later, all is fine, brake free. Take the front wheel off again, and the same thing happens.
So, I changed the cylinder piston in the master cylinder, adjusting the piston stop bolt as directed. Result, brake binds really badly. Release adjusting bolt. All is fine, but the brake switch wont 'knock off'........
So, after MUCH hassle, I added a small piece of cable shrink wrap to the spring, and it works, just.
I just cant seem to find this happy medium between the thing binding, and the brake switch working! (By the way, both calipers are free, and all pistons return with ease, and the brake lever pressure is spot on.)
Any ideas???

[Scott_Anderson]

I haven't had problems with the calipers but I did have to replace the electric switch at the master cyl for that very reason, the brake lights would stay on. It just wouldn't release.
_________________
Ride safe.



1995 K1100LT 0302044
2017 FLHTK Ultra Limited
Garmin StreetPilot 2820
Garmin Zumo 550
Garmin Zumo XT
"One who does not ask questions is ashamed to learn" Danish proverb
1997 K1100LT 0302488(R.I.P.)
1997 R1100RT ZC62149(sold)

[charles]

there is plenty of information on doing this here and on other bmw sites [k11s have the same front brake master cylinders as the oil-head r series]. take a look here: http://www.largiader.com/tech/r11mc/.

the problem is that slight seepage of brake fluid around the piston in the master cylinder, mixed with air and water, leads to a build up of crystals [aluminium salts, i believe] in front of the piston. this inhibits the piston from returning to its proper rest position and the first symptom is the brake light sticking on. if left it will result in damage to the seals on the piston.

you need to dismantle the master cylinder, which can be tricky if the piston is trapped behind the crystals, and rub back the crystals with fine grade wet and dry. this job can be done without removing the master cylinder from the bike, or even disconnecting the brake hose, although you need to drain the fluid [you will not get air in the system if, when finished, you pump fluid back up from the callipers].

if the seals in the piston have been damaged, you will need to get a service kit [about £30 in uk] which is ... a new piston. i have done this job twice now [50k+ miles on the bike] and i have just ordered a new master cylinder[£110 in the uk]. maybe the problem is that i live in a damp country, maybe the damp air accelerates the chemistry.

i guess we have to think of this as a service item, albeit a long-lasting one. i shall put on the new master cylinder and then clean up and refurbish the old one so that next time it goes wrong i need only replace the master cylinder block. it will also mean that i can do the job [which seems always to happen when days are cold and short] in the comfort of my kitchen.

charles.

[Tootles]

Thanks for that Charles. I have already done all you have suggested, (replaced the piston/and seals, cleaned out the cylinder etc), as well as replacing the brake switch, but to no avail. What seems to happening is this. You operate the lever, but it does not return fully. You can push it back by hand, (only a tiny amount), and all is well. Now, I have adjusted the piston retaining bolt (screw) as advised by BM, namely screw in until all free movement is removed from the lever, then add half a turn. Fine, the brake light switch works instantaneously. However, the brakes lock on after a few miles!! So, unscrew slightly, until the front wheel moves without binding, and the brake switch wont knock off! I have even tried bending the spring a bit, (on the switch), but to no avail. So now, I have added a tiny piece of 'shrink wrap' wiring insulation to the very end of the spring, which does work, but the brake light action is not 'snappy', and has stayed on for a few seconds, but not every time. I did check the cylinder return spring, and assembled it in the correct manner.
real head banging stuff!!!

[charles]

i still think it must be a rough/high patch in the barrel of the master cylinder. this is because of my own experience. when i last serviced my front brake the light continued to stick on intermittently, but lo and behold, after a few days, it sorted itself out. i know i did a good job - well, as good as anyone on £50 an hour would have done. but i could not be sure that the piston wouldn't find some point of friction in the barrel. once i was no more anxiously hanging my hand over the back of the bike, or checking in my mirrors for reflections on cars behind me, checking for the afterglow, the whole matter slipped out of mind for more than a year.

until, that is, with the evenings drawing in, i couldn't miss noticing that the light was occasionally sticking on. i tried to convince myself that it wasn't that old problem, but what can you do? what are the options? the switch works most of the time and only doesn't work when i know it isn't working [if you see what i mean]. it seems to be worse on a cold damp morning, but isn't brought about by wet weather per se. i haven't found it to be more likely when i squeeze the lever hard than when i just brush it. it just happens sometimes [and of course, only when i look for it or notice it! the epistemology of brake lights].

i had the bike in for an mot yesterday and checked the operation of the light all the way to where the test is done. the light was going on and off nicely. then i pulled up outside the garage and the thing stayed on. i took it in for the test and luckily for me the light behaved well. as they say, the mot test is simply a record of how the vehicle behaved at the time of the test. it behaved.

when i got back to work i decided on my overspend philosophy as explained in my last post - i.e., getting a new master cylinder. the way i see it, it's cheaper than ... six tanks of petrol. i shall let you know if it proves to be the [for nothing is permanent] cure.

[Tootles]

Cheers mate! It's comforting to know that I'm not the only one with this problem!!
Having not had the full master cylinder off yet, can you tell me how the hell you get to the pin that supports the lever, the one which it pivots on? It seems to go up towards the underside of the reservoir itself, and I was expecting to find a screw head underneath the unit, but nothing.....
Dave.

[tmarshall57]

I have suffered the same symptoms and can concur with Charles diagnosis.

My understanding is that normal piston spring force should easily push out the piston to its maximum extent of travel. This then should casue the spring to switch off the brake light.

The cause of my problem was leaky seal, dirty master cylinder bore and dirty/crystal encrusted entry to piston bore.

The solution was a good cleanup of the piston bore using fine sandpaper lubricated by oil and then a good clean. I purchased the repair kit comprising (I recall) piston with new seals and spring plus dust seal.

All worked perfectly aftwerwards.

If the piston is not returning to its fullest extent then something is restricting its movement - usually undue friction between piston and cylinder bore.

Potential cause of brake light staying on - bent switch leaf?

As far as I can recall there is no information available which relates to the adjustment of the pin which is fitted to the brake lever and which, when the brake lever is pulled, causes the piston to be compressed. It is poor adjustment of this pin resulting in lack of play between pin and piston which can cause brake binding - it has happened to me. The brakes were fine when I set off - and then gradually bound to the rotors - almost resulting in a smoking wreck

The stop screw in the Clymers diagram is in fact the screw which stops the piston from ejecting itself from the cylinder. This should be fully tightened and "loctited"
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K1100RS Special Edition 1997
Arctic Silver/Black

[Tootles]

This from the K1100 workshop manual, which I have on disk....

[tmarshall57]

Looking at the K1100 Service manual (Page 272) to which Tootles refers there are 3 pins or screws pictured in the manual

1) The stop screw numbered (4) in picture but incorrectly referred to as (1) in part of the text. This prevents the master cylinder piston from leaving the cylinder. This pin can be tightned as per instructions

2) The Mounting Pin numbered (2) in the picture which mounts the brake lever to the M/C body. This pin can be tightened as per instructions

3) The pin connected to the brake lever which is clearly visible at the bottom of the picture but which is not mentioned anywhere and which can be adjusted but can be very dangerous if overtightened. I believe this pin is sometimes confused for (1) or (2) above in terms of tightening instructions
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K1100RS Special Edition 1997
Arctic Silver/Black

[Mystic Red]

Tootles, read this thread. I had the same prob.

http://www.k11og.org/forum/viewtopic.php?t=4887&highlight=brake
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Scott Hespelt, '94 K11LT
K11 OG #466

[charles]

tootles, the pivot bolt is a real pain. you can loosen it with an allen key but the thread only drives it out to just less than flush with the surface of the body of the lever. each time i've taken it out it has needed a slightly oversized torx bit jammed onto the head to give me the purchase necessary to pull it out. once you can see the head you can use needle-nosed pliers to work it out fully.

my new master cylinder arrived today. goody goody. but i will still have to get the old pivot bolt out to retrieve the lever from the old master cylinder block. [i shall be using a new pivot bolt to re-assemble the unit.]

by the way. it is probably a good idea to put a piece of [colour-coordinated] tape over the little mirror-fitting hole on the outside edge of the master cylinder block. i found that i never had any water slopping about in the plastic cover when i did this - and that water can lie there for days, hastening corrosion in the cylinder bore.