rear brake not working on z

[jimmer]

bascially i got my 1977 z650 out of the garage after a 2 year lay up. the bike starts up and rides ok apart from the rear brake does not respond at all. The fluid level is up to the regular level. i bought some more fluid and a bleeding hose. When i attached the hose and done the regular pumping whilst open and closing of the bleed nipple not enough is hapening to give the desired effect. i have taken the nipple out and blown it through and it is not blocked. FLuid does come from the nipple hole but very slowly, not with regular squirts with the action of the brake peddle as expected. Its as though the system is not holding a vacuum, or creating enough vacuum to force any fluid through. there does not appear to be any leaks anywhere. couldn't say if the pistons onto the caliper are seized or if there is a problem with the piston in the fluid chamber (this is what i suspect). where do i go from here, i don't want to buy a whole rear brake system for it as it will cost a packet. whats the best way to find the cause? some ideas please folks....

[Rickman CR]

Jimmer, I'd take the caliper off and see if the piston, (I'm assuming the caliper is the floating type with one pad secured to the caliper), is moving when you press the rear brake lever. Recompress and retry. It or the caliper float seals might be corroded and seized. You may need a seal repair kit and if the piston is badly corroded, then a replacement might be required. However a wee strip down with lube in all the right places might do the job and save some dosh. Hope this helps.

(Edited by Rickman CR at 5:52 pm on July 22, 2006)

[jimmer]

cheers rickman, i thought as much, the thing is, my bike is 80 miles away from home at me mothers. I have my MOT due back at home for monday morning. I could ride it home on just the front brake, but as we know that is crap if the weather turns bad, front brakes in the wet is not the best. I have my tools there and a manual to help me along. I have put pads in before now and had the back wheel off. The thing is, if this does not work, the only other thing i can put it down to is the piston in the fluid chamber, i presume there are kits for these as well, or is it worth just getting a replacement? just as an additional thought, when i am bleeding the brakes, should the fluid filler cap be on or off? i have tried both ways and there seems to be no difference as it is. jim

[jimmer]

the brakes have the floating type pads on top of the pistons. my thought is that they are not moving at all because there is no pressure behind them, as i say there seems to be no pressure throughout the whole brake fluid system.it must be a problem with the fluid master cylinder. but there seems to be no leakage from anywhere. The other thing is, i'm not sure if this was all working ok before i opened up the cap of the cylinder to check the fluid level, is there a chance that it lost its pressure just removing the cap? please give me some more feedback if you can, i think this bike is on a wind-up!

[hanskloss]

removing the cap doesn't change anything, sounds like seized caliper, try to push in the piston in the caliper just to check if it moves OK, if not you've found the culprit, if yes than the master cylinder piston might have a bad seal and doesn't pump enough , there is two seals on it if I remember, one to pump one to hold the brake fluid in and if the first one is damaged it might affect the braking but won't leak, just a thought

[piers belsom]

brakes, old brakes, what a joy.... do yourself a favour and remove the system from the bike, loose the fluid , strip(the brake), clean, and start again.. check the master cylinder for any signs of corrosion on the main body and the rubber, use a good brake cleaning spray and get any old fluid out. do the same with the caliper. remove the dust seal and check for damage to the piston. make sure it can move freely. use a spark plug cleaning wire brush to remove any crud on the caliper. make sure the surfaces where the pads move are not corroded or the retaining pins or the holes they go in. basically give it all a damm good clean, reassemble using copperslip on backing plates and pins and bleed.........prime the caliper and hose if you can..works for me. use a bleed pipe with a split on one end, 'easibleed'i think they are called...piece of cake to use. hope this is of use.

[jimmer]

thanks all, jim

[Rich]

You've either got an air block or the master cylinder is knackered. If there is fluid in the res and you are pumping the cylinder you will still have a "spurt" of fluid when pumped even if the caliper piston is seized. Fill the res and leave the bleed nipple alone, undo the banjo to the master cylinder and use that as a bleed nipple to allow easier escape of air and prove if the cylinder seals are gone or you've just let some air in when playing before. When you get fluid squirting out do the banjo up and use the bleed nipple to bleed from, you should get fluid squirting out even if the caliper piston is seized. When it comes out then check that the caliper piston moves out AND RETURNS under operation of the pedal. If it doesn't strip and clean / replace as above, when cleaning a caliper body also clean behind the seal.

Protect your paintwork before doing this as brake fluid makes a good paint stripper.

[rickman CRR]

Jim

How did you get on with the brakes?

[Jim]

Still messing about with them, i might have another go tonight. Priming the calliper and the bango, (i presume connecting pipe) has been advised, will give this a go. I am sure it is just an air lock that is not shifting.