i need to push piston in on renualt senic 55 plate rear calipers?

I think you'll find that you can't just push the pistons back in, you have to 'wind' them back in. On most cars that need to have them wound back in, there's a cut-out in the end on the caliper piston so that you can either use the special tool, or use a flat metal bar, of the right thickness, to turn the piston and wind it back in. Unfortunately I can't tell you whether yours will be clockwise or anticlockwise, it's bit of trial and error.
Best of Luck
Wyn

Wyn
July 2007

Some foreign cars need the piston screwed back in as they are pushed,when you apply the handbrake the piston screws out to take up the wear in the pads,the top of the piston may have a slot in it or a couple of notches for a special tool.

Anon
July 2007