trouble with rear brakes

[geko]

Hi, i am having trouble bleeding my rear brakes. Firstly when i pump the brake pedal the bit that the rod pushes into the master cylinder doesn't always return straight away, after pulling the master cylinder apart and reassembling it then it will work fine for awhile then gets slow to return again. Secondly i hav been trying to bleed the brakes by sucking the air out using a hose attached to the bleed nipple but when i tighten the nipple back up i can still suck a little air through it. Could anyone please shed some light on the either problem for me as i dont completely understand how it all works. thanks

 

[bulldog93]

<iframe title="YouTube video player" class="youtube-player" type="text/html" width="480" height="390" src="http://www.youtube.com/embed/EGEkmWX1NM0" frameborder="0" allowFullScreen></iframe>

Hope this helps.

 

[DHZ_XR8cing]

You will find that if you have air trapped in your brake system your going to have to take off your brake system and bleed it with the caliper higher than the cylinder. Air will rise up through the fluid and bleed off.

 

[geko]

thanks for the suggestion bulldog but i had already tried this with no luck

 

[geko]

tried that too DHZ, still no good, thanks for the idea though

 

[DHZ_XR8cing]

they are a nightmare. They take alot of work when they are been stubbon. Sometimes you have to tap the caliper and brake line to get the air lock moving.
Did you do it the same way as the video showed you but with the caliper mounted higher than the resevior?

 

[pbk]

you dont need to take them off you just need some patience

i got this tip off sean01 and it worked for me today

take the rod out that goes into the master cylinder and get a screwdriver or something else long enough so you can push the master cylinder thing (i dont know its actual name) as far as possible now bleed your brakes normally using the scewdriver instead of pushing no the brake pedal

so push with the screw driver and crack the bleed nipple

tighten bleed nipple and release

repeat process till no more air bubbles come out and also remember to keep topping up your fluid or if it gets to low as your doing it your gonna suck more air in

 

[geko]

thanks heaps guys for all your suggestions, spent a couple hours today trying all of them and just when i start to get a fraction of brakes more air appears even after putting enough fluid through to fill the system 2 times over. think maybe i have an air leak somewhere, thinking either the master cylinder seal is dodgy or like i said in my original post seems that the bleed nipple isn't seating properly and is letting air back in if that is possible. had to give up for today before i lost the plot, will try again and if not guess i'll bite the bullet and purchase a whole new system. thanks again though everyone i really do appreciate all the advise.

 

[Cactus Jack]

You've either got a leak or you've let the reservoir level drop which allowed air to get into the line ... Once air is in the line it will not travel downwards ... it'll sit there where you can't see it and will cause problems until you get the line higher than the master cylinder ...

If you have a bad master cylinder piston seal or leaking line you'll have fluid running out ... so you'll know all about it ... No fluid leaks means you've got air trapped in the line ...

 

[Cactus Jack]

With car master cylinders I've copped a problem where a seal on the piston had gone and that allowed the fluid to bypass it and get pushed back into the reservoir (short circuit) instead of pressurizing the slaves ... but that was on a tandem master with front discs and drum rears ... 'not sure if it can happen on bikes ...

If you use a big horse syringe attached by nylon hose to the bleed nipple on the slave , you can bleed brakes without moving the master piston ...

You can also just use a really long nylon line and suck the fluid thru with your mouth ...

Just make sure you keep the master reservoir topped up ... a one way medical or aquarium air valve in the nylon line close to the bleed nipple prevents fluid or air from back flowing ...