Rewinding inner pistons

[misteralz]

Rebuilding my rear calipers at the moment and I've got the pistons all nicely cleaned up, the handbrake lever working, the handbrake piston retracting after letting go of the handbrake, new seals waiting patiently, but...

I can retract the pistons easily - the outer ones are fine. The inner ones, well, they retracted for a bit then stopped dead. I can wind them back out again, but they aren't for retracting past a certain point. And that point isn't all the way in. So before I give up and send them away, is there anything obvious I'm missing?

Thanks!

[jackstowers]

Do you have a manual? The adjusters accessed through the swing arm are for setting the clearance which I understand is all apart of how the handbrake works. Have a good read up before sending them away as it makes sense eventually how it all works

[914 KEV]

I find that the cause of the sticking is the caliper metal casting.

Between the inner rubber seal and the dust boot this part of the casting can rust as this part of the casting isn’t plated very well; the surface rust rubs against the piston.

This is one of the usual causes of a sticking piston on the 914-4 calipers.

[misteralz]

Useful, thank you. I thought I'd cleaned the outer lip up reasonably well, but you reckon that it's inside the caliper itself? I haven't had the pistons out completely for fear of not being able to get them back in. Do you think that may be worth a shot afterall?

Thanks!

[Mr Pharmacist]

I had a similar issue with mine - I think I just kept on winding with a bit of pressure on the piston and eventually it started moving as it should

[davep]

There should be no issue of popping the pistons out completely. I've done that for 30 years. They just thread back on; generally I press them in with a finger while using the adjuster to turn the gear. It gets tight as soon as the piston skirt gets to the O-ring. I have the proper kind of lube, so that makes it easier. Popped out one inner piston last night and what a load of crap inside of it; not the mechanism, the rust and crud.

[misteralz]

Excellent, thank you guys. Will do that in the week, or if I get some free time at the weekend.