Seizing front ally calipers
Turbo Mini Forums

So I've been running mini sport alloy 4 pots for years now and on Friday night I did a track day at donington and they started seizing.
The Pistons wouldn't return without pushing the pads back in. Every time you press the pedal it sticks again.
I couldn't work out what was the problem unless it was purely overheating.
Are the Pistons steel? And would they heat up faster than the alloy causing this problem?

They are solid 7.9 inch discs with 1144 pads.
I ran 1155's for a while but couldn't get heat into them. It seems like once they cooled down they were OK as they were stuck solid when I put the car back on the trailer but by the time I got home it rolled off on its own.

Any experience/ideas appreciated.

Thanks

Could well be the heat.. i warped some discs once from heat.. it was ever so slightly but enough to boil them and brakes would stick on.. cool down theyd be fine.. drive for few miles without pressing brake pedal and theyd still stick.. as soon as i changed discs the problem stopped

Master cylinder could cause it. When they are stuck on see if cracking the bleed nipple off releases them.

How old are they and have you ever cleaned the pistons and bores?

I dont know of any of the direct fit alloy calipers to have dust seals, so its quite possible for them to suffer dirt ingress, score the puston bore and start to corode the aluminium.

Master cylinder is a 1inch AP one. Not standard mini if that makes a difference.

I'll take them off and have a look for any dirt. I'll also try the pedal now things have cooled down and see if it makes any difference. Just not had chance yet.

It's got to be hydraulic. If they were seized on corrosion or dirt or whatever then they'd stay seized! The fact that they do release means either a hose is collapsing, the master isn't returning properly, or maybe the pushrod needs shortening a fraction.

Just reading this old post.. Tom (or anyone else) can you elaborate on why the pushrod needs shortening. Is it because its the wrong pushrod, i.e. one for a servo?

If it is too long, is it pressing too much into the master cylinder (not being able to travel further) and forcing a jammed situation?