Back brake bleeding troubles..

[Shayite]

Having big problems with this, seem to have an airlock I cant sort?

Have managed successfully to get fluid going through well 3 times with lever tightening up, with only very tiny bubbles coming into the fluid bottle at the bottom. Have then closed bleed valve up but cannot get enough fluid pressure to pump piston far outwards as need to replace it. Now cannot get fluid moving down through master cylinder at all even though can get rid of a few big bubbles through bleed tube now and again.

I have not let cylinder empty so letting air in through the top.

Any ideas?

[btbloke]

I use a rubber self bleed hose from the local motor factors, attach and undo the bleed screw while I have a bungee or strong rubber bands round the brake lever to apply some pressure. Then when it's undone I operate the lever pulling on slowly and letting off at half the on speed, slower is better than faster as it gives the master time to refill. when the fluid has gone way down in the resorvoir I refill while I have the lever pulled in, you should expect to pull on and off at least 6-8 times and refill at least twice and then I pull on and strap it with a bungee or something to hold it on while I retighten the bleed screw.
Remember to wrap a rag round the resorvoir to catch ay spillage and you should be able to push out the caliper piston when bled, if it does not bleed then you may have a knackered seal that is letting air in,check for any leakage around the seal while applying pressure on the lever when the bleed screw is closed.

[Titch]

Have you tried back filling with fluid...????

What I mean is to push fluid into the caliper via the bleed nipple using a syringe.

I was having problems with my rear brake when i was doing a rear end conversion, and I found the seal in the caliper to be faulty, and letting small amounts of air back into the system... obviousley though I had to get the piston out, which sounds like you are doing the same... just a thought.... are you taking the piston out to replace with a new one, or putting it back in again...??? as if changing then don't need to worry about damaging the old one, and just a grip of it with some pliers or grips and twist it as you pull it out of the caliper (as thats all I did...). And since a new caliper seal is only a few quid on Ebay, then just get a new one for you put your psiton back in, as then at least you know it is a good seal.
When I did this I found that I got pressure stright away when I conected it all back together again...

Lastly, where in W/Yorks are you, cos I'm only in Oldham, and if really stuck might be able to give you hand with it...

Titch

[Shayite]

Thanks for the advice, no leaking fluid in hose so may be air coming in from piston seal.

Need to get bike back on road for work tomorrow, so need to get it sorted today.

Am close to you Stumpy, bike currently in dads garage in Halifax (Sowerby Bridge end) which is just over t' moor from you, if cannot get any joy will go and get a car back bleeding kit today..

[Steve3]

Don't know if this is relevant to TA rear calipers, but it's something I learnt from many years of old BMW airheads with Brembo calipers.

Try taking the caliper off the bike, and positon it with the bleed nipple higher than the brake hose. Obviously place a piece of wood between the pads.

The old Brembos were well known for holding onto air bubbles if bled in their normal position.

[Windmill John]

Persevere with bleeding, It's amazing how long it can take if you can see even tiny bubbles in there.

[StumpyFingers]

Check the condition of the slave cylinder.