Rebuilt brake - now not bleeding through

[Revilo18]

Hi there,
I was wondering if anyone has rebuilt the rear brake system (caliper clean, new seals, new rear mater cylinder becuase the old one was knackered) put it all back together after removing all of the old fluid from caliper, lines cylinder etc, then filled the resevoir pumped the brake to sart bleeding into some tube and a jam-jar, only to find nothing coming through from the reseviour to the cylinder.
I can't get it to bleeding bleed.
The new (second hand) master cylinder all looks in good order. I spoke briefly to a friend who said I might have an airlock in the system.
When I pump the back brake lever air does comes out of the bleed nipple into my rubber tubing. It seems like there's just nothing coming through to the actual cylinder from the resevoir....?
Anyone know of a good way forward?

Thanks,

[His Dudeness]

it can be a right pain in the harris sometimes. try opening the bolt on the reservoir and bleed the reservoir. when you get fluid coming out of the reservoir tighten down the bolt again before the lever bottoms out. then try bleeding at the bolt into the caliper. then at the bleed nipples in the caliper. patience is the key sometimes

[Revilo18]

Thanks - I'm not getting anything through to the master cylinder - so when i remove the banjo bolt from the top of the mater cylinder,i look down and it's empty - despite all that pumping....
The fluid doesn't seem to be making it from the resevoir under the back seat into the cylinder. When I first filled the resevior after linking it all up, it gave off a good few bubbles - but only enough to show that the fluid has made it as far as the joint of the vertical hose to the clyinder and no further.....
I'm thinking dud master cylinder - but before I installed it I gave it a good once over and it seemed fine.
Is this a common problem?

[His Dudeness]

its possible there's a problem with it but its most likely trapped air. try taking off the bolt at the master cylinder and then priming it with some brake fluid by pouring some in where you taken the bolt out. then put your finger over the hole and pump the lever. you should feel pressure on your finger and it should get the fluid flowing. but remember brake fluid is poisonous i think it attacks your kidneys so wear gloves

[Revilo18]

Thanks - will give it a go this evening and report back.
 

[ade the blade]

if all else fails, mop out / drain reservoir.......get a nice size syringe....fill with brake fluid.........attach to open end of tubing.............squeeze down syringe whilst cracking open the bleed nipple ( minimize air intake into the system! ) and gently `back-fill` the system. if you need to add more fluid to the syringe MAKE SURE YOU SHUT THE NIPPLE ON THE DOWN STROKE FIRST KEEPING THE DREADED AIR OUT !! refill and repeat. good luck. its worked many many times for me in the past and is still the no 1 method a lot of people i speak to stick with.

[Fazerider]

I had the same problem myself earlier this year. After trying everything I could think of to persuade the fluid to flow through, including copious amounts of bad language, I took it apart again... only to discover I'd installed the master cylinder components backwards.

[markbubble]

mine was a pain also but i took it off (leaving all hose etc fitted)and lifted it slightly this seemed to help and get started,iv in the past removed bleed nipples and used syringe to get some fluid into the brake!i did the back (inwards of caliper) 1st then outside and repeated but you could try both together etc etc good luck with it 

[Revilo18]

Many thanks all for useful tips. Glad to say it's all working well now - way better than before I serviced the brake. For those with similar trouble, the main advice that sorted out my problems was
1) checking each stage resevoir, cylinder, main line, caliper  - bleeding through as you go.
2) priming the cylinder and filling the caliper from the bleed nipple using syringe or pippette.
3) patience, patience patience.
Thanks again.

[Revilo18]

Ok so maybe I spoke too soon!
I've been running the bike for the last two days fine. I come down to go to work this morning and the back brake is gripping the disc. Not completely but enough to mean I'm on the GD bus - the heat build up if I rode it with the brake half on would be huge!!
So annoyed as this was the original reason I did all the work on the brake   - it kept gripping the disc at random times even though I didn't use it. When I release the banjo bolt a quarter turn, a v small amount of fluid comes out of the bolt and then wheel can then move freely again and it's not gripping - so it's not the pistons, seals etc etc as they are going back in fine once the fluid has somewhere to flow back to  - its something to do with the fluid not coming back when the brake lever is released. However it seems to happen whether I use the brake lever or not...... This is a new master cylinder so I'm really at a loss what to do next.
Is this just an airlock and I need to re-bleed?  or something more serious? Would anyone recommend replacing the lines just to be safe or is that a waste of $$ and time.
Thanks and apologies to those that thought this was over.....

[His Dudeness]

it probably is the seals in the caliper. they swell overtime and you get a bit of corrosion in behind them so they don't release the pistons freely. if i was you i'd get a new set of genuine seals.

[69oldskool]

 
I'm thinking you may still have an airlock in the pipe?-
It's a stupid u bend route from master cyl to caliper.
 
I had a right job when i swapped over to a thou caliper, & mine was binding also.
 
Tried all previous suggestions(& they do help the bleeding process) but ended up hanging caliper from the bungee hook under seat with a 5-6mm metal plate wedged between pads & bled it that way.
No problems since,
might be worth a go before you start dismantling?