Introduction

[Dark Angel]

Hi, I'm new to the brick world, not so much to bikes in general but I'm finding these things have some distinct quirks.
I have a K1100RS which is mostly a LT under the covers due to the actions of previous owners.
I've had the dreaded "rear brake failure warning light" event (fire) and am working on fixing the not insignificant damage as I get the money for parts.

[Laitch]

Welcome to the scrum, Dark Angel. Post a photo of those brake calipers and pads. Many of those here likely haven't seen them—a sight to behold!

[frankenduck]

I has a final drive boot catch fire once. I was following a prospective buyer riding a K100RS4V that I was selling. When the rear brake locked up due to the piston getting stick in the master cylinder and the dumbf**k kept riding until the rotor heated up enough to make the rubber boot catch fire.

When he finally pulled over I threw my gloves off and quickly grabbed a rag out of my bike's tail cowl. As I was using the rag in my left hand to put out the fire from the left side of the bike I inadvertently put my right hand fully on THE EXHAUST and burned the living crap out of my right palm and fingers.

When I got home it took a bucket of ice water and a whole fifth of Crown Royal to make the pain somewhat tolerable.

I only had to replace the boot to fix the bike though.

[Dark Angel]

Welcome to the scrum, Dark Angel. Post a photo of those brake calipers and pads. Many of those here likely haven't seen them—a sight to behold!

Ok, here goes.  I did read the advisory about photo size so here goes.  I'm used to riding a 650 twin, it's been a while since I sold my beloved R1150RT (still wish I hadn't), so the torque of the K1100 hid the dragging brake quite effectively.  I only noticed the sparkly bits behind me because I was riding in the dark.


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[Laitch]

[natalena]

Welcome. Glad everyone's OK, for such an exciting outing. Cheers

[Dark Angel]

Just an update on the bike.

I've got the caliper rebuilt; pistons, seals, the lot.  Bled the system and discovered it's still pumping itself up and locking the pistons out.  My caliper spreader just starts to bend without them pushing back in.
I traced it back from the calipers, cracking pipe unions at each step, and the fluid would flow back right up to the master cylinder connection, but with the m/c in place the pistons are lock hard.  Stripping the m/c down the bore etc appear to be in good condition but the piston does not move back far enough to clear the port so it's a one-way system with no way for fluid to return or the pistons to retract.  I note that the instructions for replacing the brake pads in the service manual stipulate to use a caliper spreader to push the pistons back in, so this is supposed to be possible.  This leads me to suspect that someone has installed a knock-off rebuild kit with the right bore size but wrong piston design.  To be clear, the piston is not sticking.  The seal in the fully retracted position sits too far forward, covers the port, and prevents fluid from returning to the reservoir.

I appears that my adjustment of the lever was not in fact the cause of the problem, but rather the use by someone else of sub-standard parts.

[Laitch]

This is both an informative and cautionary post, Dark Angel. Please keep us updated.

[Dark Angel]

Extra! Extra! Read all about it!  Local idiot home mechanic learns something new!


Turns out there is in fact a return port in front (closer to the brake line connection) of the main port, but it's tiny and very easy to miss.  It's also blocked.  I've been soaking it in brake cleaner and periodically blowing it out with compressed air but it's just not clearing.  That leads me to suspect it's a corrosion issue in which case I won't be able to fix it.  How could it be corroded?  I'm going to go with lack of proper maintenance.  I've blown quite a lot of brown residue out of that section but since I can't get the black plastic spigot off (without breaking it anyway) I can't get at the port to rod it out.

Please, change your brake fluid regularly.  I've yet to see a BMW of any age the didn't develop problems quite quickly if this simple thing was ignored.

[Dark Angel]

In the interest of further my education I got destructive today and consider the results worth sharing.

Bit the bullet and removed the reservoir connection from the old rear master cylinder. As I thought the return (top hole in pic) was completely blocked.
I'd left it soaking in brake cleaner overnight this time and it still wouldn't blow through. That crud had to be dug out with a sharp probe. While I finally got it clear the cap that presses in there did not survive extraction, pretty much as expected. In the end I had to drive a screwdriver through the side of it and lever it out. The hole and seal ridges in the master cylinder are fine, but getting a replacement fitting appears next to impossible.

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[Dark Angel]

So I bit the bullet, dug that mess out, and did some plastic welding (yes that's a thing) on the cap to seal it up.  I pressed it all back together and left it sitting with fluid in it for a couple of days to test for leaks.  All good, so I take the wins where I get them.

Today I installed the new final drive gaiter, new rear brake pads, replacement ABS sensor, set the sensor clearance ( 0.6mm) sleeved the bare wiring where the remains of the old loom plug are, re-routed and oiled the clutch cable and put the spare in the duck-tail compartment, cleaned and lubricated the clutch lever and 'choke' lever, re-routed the 'choke' cable, re-routed the throttle cable (yes, all three were routed badly by Numbnuts), torqued all the brake caliper mounting bolts and foot peg plate bolts, and gave it a test run ... without the muffler. It never lets you forget it's a litre class engine that thing!

Took out my bluetooth speaker and put some music on to keep my spirits up. First track on the list ... Disco Inferno by The Tramps (first line: Burn baby Burn!)