1998 GMC Jimmy rear brake adjustment

When the parking brake is built into the caliper, exercising the parking brake will adjust the pistons out. If the cables are rusted tight, you can use a pliers for leverage to stroke the levers on the calipers. These calipers won't self-adjust like front calipers do.

You should find the parking brake will be in proper adjustment when the calipers are.

Word of warning. When working with calipers and you want to get the pistons adjusted out, never press the brake pedal all the way to the floor. Corrosion and debris builds up in the bottom half of the bores where the pistons and seals don't normally run. When you push the pedal all the way down, the seals can tear on the corrosion causing permanent damage to the master cylinder. I always taught my students to pretend there was a block of wood under the pedal. This applies to pedal bleeding with a helper too.

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Just keep stroking the parking brake lever on the caliper or the pedal in the car. You can't over-adjust it. If you can find a helper to press the pedal for you, you will see the pads contact the rotor and you won't be able to turn the rotor by hand when it's adjusted.

Every time you stroke the parking brake, the piston will come out a little. It will stay there when you release the parking brake. When you press the service brake pedal, the piston will also come out a little, but it will retract again when you release the pedal. On a front caliper, the square-cut seal can't bend very much, so the piston slides through it to self adjust. On the rear, the seal bends so much, the piston doesn't slide through it. When the brake is released, the seal straightens out and pulls the piston back with it. It takes the parking brake to get enough movement for the piston to slide through the seal. There's a ramp and ball setup or a screw thread that turn with the parking brake lever. After it turns a specific amount, it latches there preventing the pston from coming back. Thats why you have to remove the lever and turn the hex nut underneath to retract the piston.

By the way, did you fill the calipers with fluid before you installed them? You have to do that to fill the pistons with fluid. The air won't bleed out of the piston once it's installed. If there's air in the pistons, you'll never get a solid pedal. It's possible the rebuilder put fluid in the calipers already, but my guess is they didn't because unless it's perfectly sealed, the fluid will absorb moisture out of the air.

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