86 350x disc break question

[Dmfj619]

Can someone tell me how to get the rear disc brake piston to go back in so i can put the brake pads back in?

[Footy]

Check to see if the piston has a rust ring on it. If so you will need to clean that up. You will probably need the caliper oring kit if the rust ring is there.
If everything is clean I typically use a C clamp to push the piston back in.

[Dave8338]

^^^ I’ve also had ‘crud’ build up behind the piston to the point it will not recess back into the caliper. If the supply line from the master is plugged, you won’t be able to compress the piston either.

[ATC200X4716]

If the piston has a lot of dirt/corrosion I have pumped the brake to move the piston out some, hopefully so you can see some shiny piston, (don't pop it out all the way) and use a half inch wide strip of polishing cloth or sandpaper/crocus cloth with WD40 and wrap it around the piston to polish the back side of the piston and shine it all the way around. Then use a c-clamp to push it back in. If it is bound up still, then you should rebuild the caliper anyway so there is no harm in trying it. If you mash the piston back in with all the crud on it you are asking for trouble.

[Dirtcrasher]

It's normally crud underneath the seal or wiper ring, I use a Dremel and the tiny wire wheel to clean those grooves out, it's about the only time that type of wheel is useful! Once it's all cleaned up I use brake fluid or coat the piston in grease and press it back in evenly. Some pistons pop in by hand, I find the dual pistons that are a type of plastic often require a press or clamp to get them back in.