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[jimbobmccoy]

Hi

 In the process of changing the front brakes and have hit a stumbling block. I have followed the guide in the maintenace section and I can see what needs to be done, but when it comes to putting the calliper back over the new brake pads it won't fit because the piston needs to be pushed back. Problem is try as I might I can't move it

Does anyone know how to get it to budge or if a clp of some sort is required?

TIA

[Amarok]

Go to a DIY place and Buy a G Clamp
http://www.toolpost.co.uk/pages/Woodworking_Tools/Clamps/G_Clamp.jpg and you will crank that piston back in  Don't forget to take the top off your resovoir and put some paper towl around the neck to absorb the excess
Mike 

[jonathanh]

or get your hands on the proper spreading tool.  g clamp will do it but you risk twisting the piston in the caliper, causing a leak and damage

At the end of the day, it should be relatively easy to get the piston back in.  if you cannot move it, could it be siezed up?  if so then it is new caliper/refurb caliper time.

[Elite Pete]

You can use a large pair of grips and put an old pad over the piston to push it back evenly

[Amarok]

Twisting the piston !, I have used the G Clamp for many years and if you put the pad inside the piston it is impossible to twist as the pressure is central to the piston with pentitrating oil I have used the G Clamp to free up a 20 year old siezed piston now the spreader tool as it acts on the edge of the piston I have seen that tilt a piston over. Sorry that's my 10p's worth zero failure so far !

regards
Mike

[Kevin Wood]

Undo the bleed nipple while you are pushing the piston back, too, to avoid the possibility of inverting the master cylinder piston seal!

Kevin

[feeutfo]

Something like this, up to you if you protect the piston from the grip jaws

[jimbobmccoy]

So I should pick up a clamp and some brake fluid invade of loss from the bleed nipple?

Also, once the piston is retracted, this may sound silly, but do you have to hold it like that to put the calliper back on, and if so what's the best way to do it and then remove the clamp, or should it stat open long enough to get it back in position. 

[Andy H]

The GM calipers are a better design than most because they have a weather seal gaiter which extends with the piston and keeps the vulnerable polished surface of the piston clean. My Omega is 15 years old & high mileage and hasn't suffered from seized pistons (yet).

The normal lip seals get damaged by dirt and corrosion on the pistons but don't mind if the pistons rotate when you press them back into the caliper. The weather seal gaiter will tear if the piston rotates.

You need to take care to prevent both types of twist (rocking due to pressing off centre & rotating due to screwing in the thread on a g cramp)

I think the pistons should retract further than the one in the photo (before extending a little due to the elasticity of the lip seals)

[Ghost]

The piston will stay open untill you put your foot on the pedal. if you use the pipe grip method do it slowly and you should have no probs.
DONT forget before you move the car after doing your brakes press the brake pedal so long till you have a hard pedal again. you would be surprised how many people forget that and wounder why they knock down the fence or hit something else.

[jimbobmccoy]

Just to say, I got a g clamp and following advice got the new pads fitted in no time at all. Many thanks for the help.