Front pads changed last week using Stoptech and I am going to change the rear pads this Friday and noticed the spring wires on the rear pads. Question: does the caliber piston clips to the spring wires or the wires are only as guides to centre the the piston and prevent it from falling?
See photo, I encircled the area where I assumed the piston will seat in place.


2004 MCS R53 rear brake pads

 

It clips onto the piston.
If you're new to these rear calipers, be aware you have to rotate the piston while pushing it back into the caliper. There's special tools to make it easy but it's still possible with a c-clamp and channel locks.

 

I may need a caliper rotating wind back tool.

 

you can find this tool cheap at harbor freight or amazon. I forget now

 

You will. I had never done the rears and my experience was a little frustrating. The right tool will make it easy.
One more note. Make sure the wires are seated in the groove on the piston and not between the piston and the backing plate. The PO of my mini had the wire under the piston and the pad wore at an angle.

 

Small heads up, it can be a pain to install. Some go on easy, others do not and you end up bending a clip and bending it back several times.

 

Yep, bend it up a hair, its the gen 1 MINIs that have these to hold the pad in place against the piston.

 

A little late to the party (as usual)....
circling back to the comment regarding "dialing" back/rotating the rear calipers before installing: Yes definitely get the right tool.
Early on (many years ago), we had the rear brakes replaced on my '04 R53 by an indie garage who neglected to wind back the calipers before installation of the pads. I have no idea how they managed to fit the pads without doing so - But I do know they ruined the calipers and I wound up without Ebrake function.
Long story short - It wound up costing me $1,100 to have the rear calipers replaced at the dealer.
Get the tool.
Trust me.