Rear brake issue

[hyphen]

So, my rear brake has zero power.  It's squishy all the way through but provides no grip.  Even at a stop with the rear brake lever pressed in my bike will roll.  I thought it might be air in the line so I bled the rear (and the front and clutch while I was at it.)  I pulled tons of air from the front and the clutch line and replaced it with hi-temp fluid and saw great results.  My clutch is much more responsive and my front brake feels much stronger.  Unfortunately, the rear brake is still not functioning.

There are no leaks on the caliper, line, cylinder or anywhere else.  Everything looks fine physically.  Are there any other common things I should try before taking it to my tech friend?

[Popeye the Sailor]

Due to the upside down setup, to properly bleed the rear brake, you need to remove the caliper.

I would be careful if adjusting the rear brake-if done incorrectly, you can block of the fluid return hole in the master cylinder. This leads to nothing pleasant.

[hyphen]

Could air in the line totally prevent braking though?  Are there any other common problems that could be an issue?

[Popeye the Sailor]

Could air in the line totally prevent braking though?  Are there any other common problems that could be an issue?

I'd lay Nate's paycheck that it's your best bet. It's a common problem.

[Porsche Monkey]

I'd lay Nate's paycheck that it's your best bet. It's a common problem.

If your gonna place a bet, why not make it with something more substantial.

[Speeddog]

Some of the black master cylinders go bad fairly quickly.
Seems to be most common on 695's and S2R800's.

Try a bleed session first.
Remove the caliper and swing it around up to the top of the disc.
You *may* need to remove the caliper bracket to get the hose out from behind it.
That big snapring is a bear.

If that doesn't do it...
The orientation of the master tends to trap bubbles, so:
Take the caliper off of the disc.
Pump the pedal until the pads almost touch.
Dismount the master.
While holding the master higher at the rear, pry between the pads to force the pistons back in, so that any bubbles get pushed back out the hose to the reservoir.

[EEL]

+1 w/ everything speed dog said..

Personal experience: Over about 6 months, I noticed my rear master cylinder slowly losing brake pressure. I bled it and it gained a little braking power and very rapidly failed once again.

I have an S2R 800. If you follow Speeddog's recommendations and you subsequently lose all braking in your lines, its time for a new master cylinder

I got mine from YoyodyneTI.com. They generally have them resonably priced and in stock. If you have any questions about which to select, they are very knowledgable and friendly.

[J.P.]

On my s2r1k, I gotta bleed the rear about every 5 months or 1000 miles for me.
Wonder if a new master will fix it?
Gotten pretty good at it however, and the fluid is always fresh... besides, I thought rear brakes were only ornamental on these things.

[The Architect]

... besides, I thought rear brakes were only ornamental on these things.

I feel the same way!  Ornamental at best and mine works fine. 

[needtorque]

I have a McGyver solution that I have used for the rear brake as it can be a PITA to bleed. 

Take a squirt bottle of anything (I used a windex bottle) then pull out the top so you have just the squirter mechanism and the clear tube that runs into the bottle.  Get a very small diameter rubber vacuum line and put one end on the tube end of the squirt mechanism and the other end on the bleeder screw.  Take the cap of the fluid reservoir and loosen the bleeder valve.  Squirt away until you get solid fluid from the each pull.  Make sure the reservoir never runs out of fluid.  This worked excellent for me all three times I have done it.

[J.P.]

Do you have an underslung brake? Spent lots of time w/ my miti-vac, special bleeder valve, endless pumping. Only thing that works on my s2r1k is to take the caliper and flip it. (meaning removal of exhaust, wheel, caliper)
Any other suggestions would be greatly appreciated.

[gambit688]

It's fairly common, had mine fixed on the 800 last year and it is back again (actually first noticed it at the end of last season)

[somegirl]

besides, I thought rear brakes were only ornamental on these things.

Useful for:
- uphill starts
- riding with a passenger
- stopping in gravel/dirt

When I had rear brake issues I was very cautious about where in San Francisco I would ride, didn't want to get trapped on a steep hill.

[Smokescreen]

When I want to slow the rear tyre, I just slam my boot on it like I used to do with my bmx bike!!  I keep wearing out these DC shoes though. 

[yoreese]

Not to thread jack but, I just replaced my rear pads on my M750 with Galfers.  Do you need to use locktite?  I did torque to correct spec.  Thanks, Maurice.