Rear wheel cylinder

Welcome to 2CarPros.

Are you sure the springs are correctly placed? They should hold it in for you. What work was done? Did you replace the brakes, a wheel cylinder, hardware? Do you have the brake adjuster closed enough to install the drum? Also, could the parking brake be stuck and taking pressure off the spring and allowing the wheel cylinder to move?

https://www.2carpros.com/articles/how-to-replace-a-wheel-cylinder

https://www.2carpros.com/articles/how-to-replace-rear-brake-shoes-and-drums

Here are the directions specific to replacing a wheel cylinder on your vehicle. Take a look through the process and see if there is anything that you may be missing. The attached pictures correlate with the directions.
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Removal and Installation
Vehicle Brakes and Traction Control Hydraulic System Wheel Cylinder Service and Repair Procedures Removal and Installation
REMOVAL AND INSTALLATION
Wheel Cylinder

Removal and Installation
1. Remove the rear brake drum.
2. Using the Brake/Clutch/Service Vacuum, remove brake dust and dirt from the brake assemblies.

pic 1

3. Remove the parking brake cable from the parking brake cable lever.

pic 2

4. Remove the hold-down clips and pins.

pic 3

5. Remove the lower spring.

pic 4

6. Remove the rear brake shoes.
1 Pull the bottom of the brake shoe forward.
2 Release the upper return spring.
3 Remove both brake shoes together.

pic 5

7. WARNING: Use of any other than approved DOT 4 or DOT 3 brake fluid will cause permanent damage to brake components and will render brakes inoperative. Failure to follow these instructions may result in personal injury.

WARNING: Brake fluid contains polyglycol ethers and polyglycols. Avoid contact with eyes. Wash hands thoroughly after handling. If brake fluid contacts eyes, flush eyes with running water for 15 minutes. Get medical attention if irritation persists. If taken internally, drink water and induce vomiting. Get medical attention immediately. Failure to follow these instructions may result in personal injury.

CAUTION: Brake fluid is harmful to painted and plastic surfaces. If brake fluid is spilled onto a painted or plastic surface, immediately wash it with water.

NOTE: When any part of the hydraulic system has been disconnected for repair or replacement, air may get into the system and cause spongy brake pedal action. This requires the bleeding of the hydraulic system after it has been correctly connected.

Disconnect the brake line fitting from the wheel cylinder.

pic 6

8. Remove the wheel cylinder.
1 Remove the bolts.
2 Remove the wheel cylinder.

9. To install, reverse the removal procedure.
Bleed the brake hydraulic system.

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Let me know if any of that helps or if you have other questions.

Take care,
Joe