Anyone any ideas or tips back brake has given up !
Bled 5 times this afternoon and after a few pulls of the lever it pulls to the bars 👿
When you remove the bung from the lever a little air escapes ? checked pistons which look ropey ?
From looking on chain cycles that is the only part they sell ?
Tips ?
Ideas?
Has anyone managed to fit new pistons with success?

any help appreciated as i'm doing Mayhem with one brake otherwise 🙄

Pistons are easy on HFX's as you can split the caliper.
Often the pistons leak aroud the seal if they're old.
Bleeding can be a pig though, often taking several attempts, even with the proper bleed kit (which is a waste of money IMO)
whereabouts are you based? Maybe someone can help you sort them?

Take them off the bike and hang them with the bung bit at the very top. And push the pistons in before you bleed as air can get trapped behind them

You used to be able to buy rebuild kits for these which included pistons, o-rings etc. I would have thought the UK distributor should be able to help you out with these. Dead easy to rebuild.

Also quite cheap to replace. I bought a 2nd hand set off here when mine died, worked out cheaper than getting LBS to rebuild (I don't do brakes!)

Try operating them with the lever still upside down after bleeding, if you still have a good lever then it's pretty certain that the diaphragm under the reservoir cap has gone, or you've let air inbefore re-fitting the pin. Doubting it's the caliper pistons if the air is getting to the reservoir that quickly, though it is possible. Another likely suspect is the master cylinder seals, available for about £12 and easy enough to fit if you have small circlip pliers(also check the cylinder bore for score marks, not unheard of on an oldish set of brakes).