Rear Brake Sticking, Intermittent.

pedal adjustment, partially blocked flexy hose. pads tight in the carrier caliper requires service. if you catch it when its sticking and open the bleed nipple then the brake releas its ether adjustment of the pedal or blocked flexy.

 

Standard item is bargain bucket cheap and piss poor quality so the piston has siezed ?

 

Strip the pads out of the caliper,put a bit of wood in where the pads should be and gently pump the piston out(not right out!) then clean with brake cleaner and a bit of metal polish until it's spotless lightly grease with red rubber grease and push back in,you could also flush and rebleed the system as well,if there's a sliding caliper on that model clean and regrease the pins!

 

This often happens if the system has air in it and needs properly bleeding.
As the brake heats up in normal use, the air in the fluid expands and causes the brake to drag .. or even lock up in severe cases.
If the caliper is fitted below the swingarm (as on my monster) then its hard to bleed properly because the bleed nipple isn't at the highest point in the system (where the air tends to collect).
Solution is to remove the caliper and raise it before bleeding (I made a simple plywood bracket to mount mine temporarily in a higher position, though I was being fussy and its not strictly necessary .. its just easier that way).
Obviously, you will need to put something between the pads (instead of the disc) if you do this, to stop them popping out.
The same thing can occur if the fluid becomes contaminated with moisture (its hygroscopic, so absorbs airbourne moisture very readily). This then evaporates when it gets hot and then behaves much like the air does.

I would re-bleed as above, using new fluid from a sealed container, and flush out all the old fluid and replace with new as part of the process.
I might take the opportunity to clean the pistons (but I wouldn't grease them on reassembly .. that just attracts the dirt).
And when it was back together I would check that the lever has plenty of slack in it (grab the lever and jiggle it to feel for play).
You could try this test when its hot, if it locks up again .. to see if the slack has disappeared.

Don't ignore it.
Back wheels have been known to lock up in a serious case, which obviously has its hazards.

 

Firstly check for incorrect pedal adjustment. You should be able to feel a small amount of up and down play in the lever before the plunger engages with the master cylinder when the brake is cold. Without this, as the cylinder heats up and expands it can no longer uncover the vent channel. With the vent channel blocked, pressure can build up and lock the rear brake.
This happened to me due to incompetence on my part when fitting some rearsets. I was travelling on a french motorway at the time. Stuff expanded so much that the slave caught fire. The whole lot was wrecked; pad plates bent, piston melted, disc blued etc. No back brake for a week of riding on wet roads in the mountains. Not nice!

 

Well, its not conclusive evidence but the fact that the lever play reduces once the system has got hot does suggest that you may have residual air in there that needs bleeding out, or else water contaminating the fluid.
Are you sure that you need to remove the wheel to raise the caliper .. that's not necessary on my monster.
Does it help if you remove the pads before trying to remove the caliper ?

Could still also be a sticky caliper though, I guess.

In the meantime, if you have to ride the bike, I'd be inclined to put a bit more play in the lever.
On my monster, this entails adjusting the length of the operating rod between pedal and master cylinder, and is pretty simple and quick to do.

 

You might as well source a stand as you will need one come tyre change time,saves a lot of hassle in the future,

 

cool, seen this fault several times tow.
also seen on master cylinders a little lip of corrosion build up in the bore which stops the piston returning fully.

 

I had the same problem with my Paul Smart. I traced the problem to the rear master cylinder. Corrosion had built up not helped by the fact that it is situated above the exhaust pipe so It is subject to heat and cooling cycles.
It was ok when cold but when the bike heated up the rear brake would drag. The wheel would free off again when cold.
All the advice the other members on here have given us valid, but replace the master cylinder. They're not expensive. It will cure the problem. At the same time make yourself a simple heat shield for the master cylinder out of some sheet aluminium to protect the master cylinder from the heat of the exhaust. Replace the brake fluid with high boiling point race fluid.
I've never had the problem since.

 

I would agree with the change to a new cylinder and a higher boiling point fluid, The chap I use on the bikes at the last service put dot 5 on the rear. I wonder if there are better rear master cylinders on other models than can be used on this model bike or an after market upgrade?

 

Even a rear brake system bled of air in perfect condition will show reduced play at actuating link when bike has been ridden/good and hot.
I'm not sure of the way your master cylinder is located in proximity to the exhaust, but I can remember approx 3 mm free play (bike cold) on a 748 during summer weather being perfectly acceptable.

 

Wouldn't recommend putting dot5 into a brake system unless a complete reseal and new brake line,silicon fluid and ye olde dot fluids aren't compatible!

 

yip. dot 5.1 if your going up a notch.

 

Agreed about the master cylinder, had the same with my 999. Think the exhaust had cooked it after an extend session setting up the tps which cooked the rear light lens and the end can carbon cover.