Rear disk brakes, can't get the caliper piston back in


Has anyone had a problem getting the caliper piston back in on rear disks?


OK, a little more info, due to the parking brake mechanism you cannot just squeeze it back in with a c-clamp like the front, it must be spun in with a special tool (which I have). But this one just spins, my friend says it needs to be pushed and spun to catch the threads inside. How can I push and spin at the same time? Any other suggestions are appreciated. The car is an '04 Mercury Minivan.


Year, make and model of the car would help, and anytime you post on this forum you should ALWAYS ALWAYS ALWAYS include this information, as well as mileage, and any other potentially useful information (date last serviced, recent failures and repairs, etc.)

Your problem lies with the parking brake. There are two different kinds of rear disc brake parking brake systems. Yours is undoubtably the kind of system that uses a lever attached to the back of the calpier to actuate a mechanisim within the caliper that pushes the piston and ultimately the brake pads, holding the brake. That mechansim automatically adjusts itself as the pads wear down. When you replace the pads, it’s gotta wind back up.

What you have probably been trying to do is force the piston back in with a C-clamp or simmilar device. On some brakes that will work, but you have to remove the lever from the back side of the caliper. It’s attached to the parking brake cable. You probably had to detach the cable to replace the pads. If you didn’t detch the cable now, then detach the lever from the caliper, and try pushing with the c clamp. If that doesn’t work, and the piston has notches in it, use a pair of plyers to grab onto those notches and turn the piston back into the bore.

Make sure the cover is off the master cylinder reservior.



[b]If you look at the piston for the rear brake caliper, you’ll see some sort of feature on the face of the piston. This where a tool is used to rotate the piston back into its bore, while at the same time compressing the piston.

Go to your local parts store, and look for a tool that rotates and compresses the piston back into it’s bore for rear disc brakes.



be sure the bleed screw is undone before you spin


Try calling your Mercury dealership or Napa. There is probably a special tool for this.

Replaced the brakes on a 1988 Grand Prix once. Luckily, I had my wife’s cousin to help me. I don’t recommend this as it will probably scratch the heck out of the piston, but one person used a C-clamp (gradually tightening) while the other used channel lock pliers to twist. I remember one side turned clockwise while the other side turned counterclockwise (not sure which side was which).

Try to find a tool, though first.


Detaching the lever and pushing the pistion back in with a c-clamp always works for me (Pontiac 6000). Sometimes I have to nurse the shaft along with a wrench though, just to make sure it keeps turning.