Morning all from sunny Northumberland.

I've got the leaky rear calliper off my X350 at the minute waiting for the arrival of a set of seals.
Just out of curiosity I was wondering what the internal components of the piston do. There's a type of thrust bearing and a seal in there and I suspect it's that seal that's leaking because downstream of it there's a drilling which connects to the external groove of the piston which is where the fluid seems to be coming from.
I've looked in the usual places but can't find any info.
Just wondering if anyone would be kind and clever enough to explain what it all does.
Thanks
Pete

 

I have never seen an 'exploded' diagram of the parts, but as the handbrake is provided by the hydraulic pistons of the main brake, there will be an internal mechanism operated by the handbrake cable that applies pressure to the piston. There will also be some sort of compensator mechanism to allow take-up of excessive movement as the brake pads wear. This isn't necessary for the hydraulic side of things.

 

Inside the piston there's a circlip holding several strange shaped washers, a ball bearing type thrust race and of course the mystery seal. Foolishly I removed the circlip and inverted the piston when of course everything fell out onto the bench. I think I worked out how it works and put everything back where I thought it should go with new seals all round. Touch wood it seems to be working and not leaking.
Did one of the fronts this morning and that was a doddle, Interestingly it was a Ford item.
Thanks for the reply