back brake not working

[hodgerydoo]

Back disk brake not working and brake light doesn't come on when pressing brake pedal, i'm thinking it is seized up due to salty roads?? Any ideas?

[knobbly]

It's more likely the brake will seize on the disc due to the pistons not returning freely. Try lifting the back wheel off the ground and try turning thr wheel by hand. If it's hard to turn with the brake off then you need to take the caliper off and refurb it.
If it turns freely the try applying the brake while turning the wheel at the same time to see if the brake is actualy applying pressure.
As for the light, it depends on how the light is switched on. Is there a spring attached to the pedal? If so then spray loads of WD40 over the switch at the other end of the spring or adjust the switch. Is the lever/pedal actually moving? also what bike is it?

[hodgerydoo]

No, brakes not seized on cos wheel turns i was thinking it is seized off? yes pedal is moving ok but reaction on brake is nil, have checked fluid and thats ok. Bike is a derbi terra. brake does not seem to be applying any pressure though.

[scouse]

Check your master cylinder - sounds like the bore maybe gunged up and there is no pressure

[Freeloadeur]

Are the pads actually moving at all? Get a mate to push the brake pedal while you check the calliper. How worn are the pads, and have you been anywhere near the disc or calliper with any lubricants? Did your bike sit outside at night? There was a spate of kids round me spraying WD40 into bikes' brakes for a laugh recently. They got mine and that sure made my back brake seem like it wasn't working. A set of new pads (and pants) and all was fine again.

As for the brake light I'll look at mine tomorrow to see how it's wired in.

Have you joined up to our Facebook page yet? Someone on there might have more thoughts.

[picos mestizo]

My rear brake on a Beta Alp goes like that when the pads are worn out.
Which I reckon is about every 800 muddy miles.
The pistons are restricted from coming right out of their bores by design & the pedall has excessive travel.
The reservoir is also nearly empty @ this stage as all the oil is in the calliper with the pistons a long way out.
Brakes on an Alp are AJP,yours maybe the same.

[Mike54]

pad pin fallen out along with pads perhaps? Could be one of lots of reasons. take a look and see what you can see. if you're not sure what you're looking at take some pics and post them. one from the rear close to the caliper from not quite right above, one from the front of the caliper etc. best to take the wheel off but if you're not confident leave it on for now

[Sprockette]

If it's really annoying just take it to bits, good clean, put it back together again. I believe this is the mantra drummed into every motorcycle mechanic's apprentice from day one.

[knobbly]

Right I think you have a pressure switch which like it sounds detects the pressure of the fluid.
This may sound a bit daft and obvious but is the lever actually attached to the master cylinder piston? the back of the lever will be connected to a kind of 2 pronged fork with a pin through it. Has that pin come out?
If not I would get a meter, unplug the light switch and see if you are getting volts when you press on the lever.
I would take off the caliper, push the pads in and press the lever a few times to see if they come out (not too many times as most bikes brake pistons are just like cups and will fall out if you over do it).
Oh and dont disconnect the brake hose when you take off the caliper.

[knobbly]

Found this