rear brake no workie

[mnb]

So back in March or April, I discovered the rear brake pedal on my K11LT went all the way down, providing at best 5% braking power compared to normal.  There was no sign of leaks, although crystallization was evident near the boot on the master cylinder.

I picked up a used master cylinder on eBay for $70.  I pulled that one apart and cleaned it and inspected the piston and various removable parts, which looked to be in good condition.

Having no place to work on bikes, I mothballed the bike since I wasn't working at the time.  Now that I am, I took the bike into the shop.  Explained the symptoms, what I noticed and provided the used master for parts as necessary.  I rode of on a loaner Vespa for the day.

End of the day, I get a call, bike's ready.  I pick it up, drive home.  I'm nearly home and I realize the rear brake isn't working.  I don't recall actually using it leaving the place.  Pretty much the same symptoms.  Pedal goes all the way down, virtually no braking power.  I got home and checked for fluid leaks, found no sign.  I pumped the pedal in case it was a bleeding issue, but that didn't help at all.

The shop used the internal parts from the used master I provided since the ones on the bike were pitted or corroded.  They did not use the entire master, though.

So it'll be two or three weeks before they can make time for this again.  I do not have the facilities, tools or time to work on my bikes.  But for $100/hr, I'd kind of expect a rear brake they just worked on to be checked well enough to notice it's not working...   :hmm:

Any suggestions on why it's not working?




Apparently the output seal on the input side is leaking, too.  The bottom of the engine is wet.  No oil on the ground at least.  The clutch isn't slipping at least.  That's probably about $1000 to get fixed.  Lots of labor.  More unwelcome news.

[mystic red]

But for $100/hr, I'd kind of expect a rear brake they just worked on to be checked well enough to notice it's not working...

Ya think! I'd blow up on their ass. Then after they fixed that I'd find a good independent, buy him a Clymer's if necessary, and let him do the work for probably less than $50 an hour.

[Rick G]

Pump the pedal and feel and look for swellings on the lines. sometimes they bleed well and will work a little bit when the pressure hose ruptures but the outer sheath doesn't and it blows up as fluid is pumped into it then sloely goes down when you stop pumping. The result is no brakes but no fluid leaks as it is contained within the sheath.

[Motorandy123]

They can leak internally, there are 2 plungers one seals the outside and one pushes
fluid into the line. I'm surprised they used used parts. A rebuild kit is $60 and
 a new one for around $129 at Beemer Boneyard.

[mnb]

They can leak internally, there are 2 plungers one seals the outside and one pushes
fluid into the line. I'm surprised they used used parts. A rebuild kit is $60 and
 a new one for around $129 at Beemer Boneyard. I'm looking at the same problem
but only want to spend $25 for a used one.

They used used parts because that's what I provided them.  A rebuild kit is $90.  A new master cylinder is over $300.

Most of the lines for the rear brake are solid metal.  The only flexible line is the one from the reservoir to the master cylinder.

[robleyd]

The only flexible line is the one from the reservoir to the master cylinder.

That isn't under pressure when braking so isn't an issue. However the flexible hose to the calliper may be.

[mnb]

The shop owner took it out for a test ride when I brought it in yesterday.  He seemed to think it needed bleeding, but agreed it was in bad shape... not much braking power at all.

They tried adjusting the brake pedal (this indicates how poorly their mechanics understand a braking system), which merely moved the pedal down.  It still bottomed out in the master cylinder.

So they rebled it.  And it's fine now.  Of course, they failed to adjust the pedal back, so it's a bit low now.

Other than to the shop twice, I've ridden the bike once since Christmas.  It felt good to get back on the K. 

[frankenduck]

Be careful.  If that pedal is adjusted too low then the piston can get stuck on the set screw, locking your rear brake up some, heating the rotor and lighting the swing arm boot ON FIRE!

[chrish8846]

Or melting the cover on the Brembo and toasting the pads.

[mnb]

Be careful.  If that pedal is adjusted too low then the piston can get stuck on the set screw, locking your rear brake up some, heating the rotor and lighting the swing arm boot ON FIRE!

It's fine.  They didn't adjust it THAT much.  It's just lower than normal.  I'll probably put it back to normal tomorrow while I deal with some minor maintenance on various bikes.