Boiling over.

[BerettaRacer]

So took the mighty K12S to the local aftermarket shop to get general maintenance done after a two week, 3200 mi trip down the east coast (including the 2022 FART), Skyline, Blue Ridge, Dragon, Cherahala, etc. And the very last 6 hrs coming south down central/south Fla. thru the leading edge of hurricane Ian. 

 

-Tires. Changing from Dunlop Q3+, to Dunlop Roadsmart IV for more life.

-Oil & filter

-Brakes. I had front pads changed a while back and all is fine there, but now rear rotor was showing some light scoring, and pads were unknown to me. (Bought bike with 20K) So doing new rotor and pads.

 

Leaving the shop (relatively quiet road with about 1/2 mile straight flat road) I began to break-in rear pads/rotor. First few 30 mph stops (rear only) had very little stopping power. Began to smell normal burn scent and next few stops got better. Began picking up the speeds a little to the 40-50 mph range, and was beginning to get some decent stops, right up to the point of feeling the ABS kick in. 

 

On the next stop all hell broke loose. 

 

Mid brake lost rear brake entirely, pedal dropped away to nothing. Immediately thought of catastrophic failure, but began pumping and got a little pedal back. Tried it again and same result. Pulled right back into the shop, originally thinking I was low on fluid, maybe leak in system etc. Fluid was full but no rear brake at all. Tech wheeled bike back into shop and on lift. He began an inspection, nothing obvious, but rotor and caliper were extremely hot. Once things cooled a bit he did a bleed and got some brake back. 

 

General thought was that I had boiled the fluid. So he did a system flush & bleed. I made the 20 mi ride home and all seems well now. Will test more this weekend, may run down to the Keys.

[Lowndes]

I had a very similar problem this last weekend with the hydraulic clutch on my '99 K1200S about 120 miles from home on a ride with the group so I broke off and rode directly back home trying to avoid stops. 

 

I found that it would give a breif release by pumping the clutch lever 5-6 times.  I found that IF I could get into neutral before a stop, then I could pump the clutch, quickly get in 1st gear and start off, then "power shift" up without the clutch.  The master cyl still shows full fluid in the reservoir but there is fluid coming out under the trans.  Got to be the slave cyl.

 

Is that similar or related to your rear brake problem??  Dunno, but I'll get into it this weekend.  I never use a rear brake, don't even know if mine work or not.

[dirtrider]

35 minutes ago, Lowndes said:

I had a very similar problem this last weekend with the hydraulic clutch on my '99 K1200S about 120 miles from home on a ride with the group so I broke off and rode directly back home trying to avoid stops. 

 

I found that it would give a breif release by pumping the clutch lever 5-6 times.  I found that IF I could get into neutral before a stop, then I could pump the clutch, quickly get in 1st gear and start off, then "power shift" up without the clutch.  The master cyl still shows full fluid in the reservoir but there is fluid coming out under the trans.  Got to be the slave cyl.

 

Is that similar or related to your rear brake problem??  Dunno, but I'll get into it this weekend.  I never use a rear brake, don't even know if mine work or not.

Morning Lowndes

 

NOT unheard of on the BMW 1200 bikes, the K bikes have a similar hydraulic clutch system so probably the same issue.

 

I presume that your problem showed up after a long stretch of freeway riding without using the clutch or shifting? 

 

If so then probably the slave cylinder piston is vibrating slightly then sucking in air.

 

On the 1200GS bikes there was a BMW service bulletin to cut the clutch line zip ties then route the clutch line as straight as possible on it's way up to the master cylinder. (basically eliminate any high & low areas that could trap that air). This allows the air to move up the clutch line all the way to the master cylinder reservoir.

 

If you can get the front of the motorcycle WAY up in the air, like up a very steep driveway, or up on a curb, or even just the front tire up on your motorcycle lift then set the clutch lever to max travel. Then pull the clutch lever all the way in then allow it to snap back out a number of times. On the 1200RT/GS once you start to get some clutch operation & feel back they will usually bleed themselves as you ride & use the clutch so I presume that your K bike will respond the same.   

 

If the problem did in fact show up after a long clutch-free freeway ride then usually cutting the zip ties and rerouting the clutch line prevents future issues but also using the clutch lever a few times (downshifts etc) on longer freeway rides usually prevents the problem from returning.

 

If you need get into understanding this in more detail then you should probably start you own thread then we can address it there.

[Lowndes]

Wow.  Thanks for the info on this, Dirtrider!!  I could NOT figure this one out.  Exactly as you said, "a long clutch-free freeway ride" right before this.  Thank you, sir!!

[Lowndes]

BarettaRacer, (back on topic here) what type brake lines are on that rear brake, the flexible portions of the lines??  Are they the OEM lines??

[BerettaRacer]

16 hours ago, Lowndes said:

BarettaRacer, (back on topic here) what type brake lines are on that rear brake, the flexible portions of the lines??  Are they the OEM lines??

All stock OEM. Only thing not OEM is the new pads.

[Lowndes]

I had a front caliper clamp down and not release several years back on a ride.  The disc and caliper got very hot.  The only way I made it home was it started raining hard.  I had to disassemble the calipers to clear it.  The OEM flexible"rubber" lines were decomposing from the inside with pieces falling down into the calipers where they collected in the drilled passages between the calipers and formed a kind of check valve.  This clump of black rubber junk would let DOT4 into the pistons but not let it out, just like a ball check valve does.

 

If your situation is similar to mine the solution is a new PTFE (sometimes referred to as "braided SS lines") brake line kit for your bike from Galfer, Speigler, or others.  Many options on colors of the lines and fittings.

 

It's pretty well understood that DOT4 is not good for paint and plastic, and some kinds of brake lines, like BMW's.  They seem to last 15 or so years and either have an aneurysm type burst or the crud clogs up something.  It's not the miles, it's the years.

 

It cost me about $210 for the complete kit for the clutch and front and rear brakes.  It took a Saturday afternoon in the garage to replace all the lines and bleed the systems.

 

The plug:

 

 

The mating half: