K11 Owners Group

[cracked canoe]

good Morning,

finally finished with the battery. All is back to normal. driving smooth. thinking to myself, life is grand.
should have know better than to be too complacent......

New battery two days ago, back brake fail today.
Then again I need to tell myself.. Self - the bike is pushing 30.
anyway...
on my way into the office, the back brake failed.
checked it out in the parking lot and drip, drip drip.. .
leaking fluid from the rubber parts just behind the metal foot pedal.
small drips as I press on the pedal
wondering any advice?
Is this a difficult job to replace the unit.

not sure what i should be looking for in order to better trouble shoot the issue.
any suggestions on where to start? I feel i might be getting better on the tools but still not mechanically inclined in any capacity.
I still require a paint by number road map.
thanks in advance

Cracked Canoe

[John Clauss]

Sounds like the rear master cylinder is having issues. Brakes are sealed systems and need pressure to work. If it leaks fluid, air gets in and air will compress, whereas brake fluid will not, and that is what activates the brake.

The master cylinder can be rebuilt, but if it has not been regularly serviced it may not be possible. New are available, but expensive.

Replacing is not "hard" except that you need to be able to then bleed the brakes and get all of the air out. This is something that is a little more difficult because of the ABS system.
_________________
1997 K1100LT
1975 R75/6

It will bring you so close to nausea, it will make you sick! - Big Al

[N41EF]

I just rebuilt mine with a rebuild kit I got from Beemer Boneyard. Search back a month or two and you'll find my thread. Was not hard to do.
_________________
2014 R1200RT Water Cooled
2001 R1100S Light
1993 K1100LT. Nissan Ice Blue.(Gone)

[Ted]

Brake fluid is hygroscopic, meaning it will absorb water. This is a feature as it will keep the inevitable moisture intrusion from doing any damage -- up to a point. That point is usually several years, which is why brake fluid should be flushed every year. With a quart of brake fluid, 3' length of clear vinyl hose and a $10 check valve, or a Mity-Vac, this procedure takes roughly 30 minutes. Failing to do this will lead to more moisture in the fluid than it can absorb, and the inevitable corrosion it brings.

In the rear, this most often appears as corrosion and pitting in the inner walls of the rear master cylinder, the low point in the rear brakes. The rear master works by a plunger with a rubber collar forcing brake fluid through the cylinder when the brakes are applied. If the cylinder begins to pit due to corrosion from old and compromised brake fluid, the rubber collar will tear. At that point brake fluid will bypass the collar leading to insufficient pressure to apply the rear brakes, and a steady drip (or even steady stream) of the escaping brake fluid from the boot that protects the master cylinder.

Taking off that cylinder is not hard, just need to remove bolts and have plenty of rags handy. Once the cylinder is off you can inspect the cylinder walls and plunger. Sometimes a tiny bit of residue from old fluid is trapped by the collar and all it needs is a good cleaning. More often the inner walls have started to corrode and pit. If the damage is minor it can be cleaned and honed (I've heard a brass brush from a 22-cal gun cleaning kit works) and a $50 rebuild kit can be used. These kits include a new plunger, rubber collar, and other assorted bits. If the damage is significant, even with cleaning and honing the gaps from removing corrosion will either tear the new boot or still allow fluid to bypass the collar. It is then time to pony up the $150 for a new rear master cylinder.

Drake has done a great write up here:
http://classickbikes.com/ckb.tech/0.ckb.tech.files/master.leak/master.leak.htm

Might as well call Spiegler and add new SS brake lines while you are at it, you can get the rear package by itself and it is under $70 I believe.
_________________
Ted
KOG#1