You are changing the rear disc brakes on a 1994 Chevy lumina caliper piston will not screw in so you have enough room to put new pads Is there trick this that unaware of Thanks?

The caliper piston on a 1994 Chevy Lumina rear disc brake likely won't screw in because it's a self-adjusting type that retracts differently than older screw-in types. You don't screw it in; you push it back in. There are a few ways to do this:

* Caliper Compression Tool: This is the proper and safest method. These tools are designed to push the piston back into the caliper bore without damaging the piston seal. They usually have a rotating head that matches the piston's shape to evenly distribute pressure. This prevents damage to the seal.

* C-Clamp Method (Use with extreme caution!): This is a less-preferred method, but can work in a pinch. You place a block of wood between the caliper piston and the C-clamp's jaw to distribute pressure evenly. Very slowly tighten the clamp. It's crucial to keep the piston straight and avoid twisting it. If you twist or force it too much, you risk damaging the seal, leading to brake fluid leaks and brake failure.

* Using a large screwdriver and a block of wood: similar to the c-clamp method, but with less control. This is strongly discouraged due to the higher risk of damaging the piston.

Before you start:

* Crack open the bleeder valve: This allows the brake fluid to escape as you compress the piston, preventing damage to the brake system.

* Collect the fluid that comes out: Brake fluid is corrosive. Use a container to catch the expelled fluid, and make sure it doesn't get on your car's paint.

* Protect your paint: Take the necessary precautions to prevent scratching your vehicle's paint while working.

If you're uncomfortable doing this yourself: Consider taking your car to a mechanic. Brake work is critical for safety, and incorrectly compressing the piston can lead to brake failure. The cost of a repair due to a damaged piston seal is likely higher than having a professional do the job safely.