I have an 07 SG and have been having intermittent problems with my rear brake.

Usually it's fine but other times it's all but flat with no rear braking power.

When this first happened I asked the dealer to check it out - they bled the brake and said it should be fine....

A few weeks later I was out of town on a road trip - same thing happened..almost no rear brake?

I stopped by another dealership and they said it was fine...it was better - maybe it had warmed up??

Now, I've ridden 9k in the last year so I know this isn't in my head. The question is..what could cause the rear brake to work fine sometimes..but die on a cold start occasionally?

 

Just to clarify...when I say cold start,I mean this only seems to happen if the bike has been sitting overnight...and even then sometimes it's fine..othertimes it's almost dead..

 

I would suspect that you may be sucking in a little air.
Not a very common happening but it does occur.
Personally I would remove rear caliper and the pads and thorough look
for any signs of fluid seepage around the pistons.
Also make sure bleed screw seats are clean and seats snuggly.
Next check the entire length hose from the master cylinder to the caliper.
Look for frayed spots, and where line is crimped to the end fitting, bend it and look for cracks.
Thoroughly check out the rear brake lite switch. I presume it is mounted same as mine.
Just below the right hand cover on the rear downtube and is a screw in. Check it close for seeping.
Lastly also check the master cylinder itself.
DOT 4 is very hard to get hot enough to boil. So I doubt that is the problem especially since you say it does it first thing NOT after a hard days ride.
NO it will not be the M/C gasket cover causing this if it is leaking, unless you have to keep adding fluid and have ran the M/C dry on fluid.
If there is a small leak in line AFTER the master cylinder when you let off the pedal the piston will attempt to draw that air back into the system.
Caliper being higher than rest of system the air would float up to the caliper
thus giving a need to bleed it.
However, if the master cylinder has ever been pumped dry, you could get air into the main bore and then push it out into the line.
Then you would need to fix the cause, refill the master, bleed the master, then bleed the caliper.

 

make sure your air suspension filler fittings are not dripping a little bit of oil on the disk. Happenned to me.

 

Thanks Choo and Beamer..the fact that it only happens occasionally might make the dealer think it's a loose nut behind the steering wheel - but there's definitely something going on. I'm gonna jack it up in the morning and check the lines again - when I put in the Tmax, I rerouted the 02 sensors and I want to make sure I didn't put a tie down too tight off the brake line. If everything look ok I'm gonna insist the dealership check it out 100%..it's under warranty and I need a reliable rear brake for slow speed maneuvers.

 

As you might imagine, there is no excuse for a dealer to say it is fine

Leave it with them if necessary and tell them to fix it

Ride Em Carry Em