Tools You'll Need:
* Jack and Jack Stands: Essential for safely lifting and supporting the vehicle.
* Wheel Chocks: To prevent the vehicle from rolling.
* Socket Set: Including metric and possibly SAE sockets, depending on your truck.
* Wrench Set: Open-ended and combination wrenches.
* Hammer: A ball-peen hammer is ideal.
* Punch: A drift punch or similar tool.
* U-Joint Separator: This tool makes removing the old U-joint much easier. A pickle fork can work in a pinch but risks damaging the yoke.
* Grease: For the new U-joint.
* New U-Joints: Ensure you get the correct replacement U-joints for your specific vehicle.
* Torque Wrench: To tighten the nuts to the manufacturer's specifications.
* Penetrating Oil (PB Blaster, etc.): To help loosen rusted or seized bolts.
Steps:
1. Safety First: Park on a level surface, engage the parking brake, and chock the wheels. Raise the vehicle using the jack and securely support it with jack stands. Remember, never work under a vehicle supported only by a jack.
2. Locate the U-Joint: Determine which driveshaft houses the U-joint you need to replace (front or rear, depending on the location of the problem).
3. Disconnect the Driveshaft: This step varies greatly depending on your truck's setup. You may need to:
* Disconnect the driveshaft from the differential: This typically involves removing bolts.
* Disconnect the driveshaft from the transfer case: Similar to the differential, this involves removing bolts.
* Support the driveshaft: Once disconnected, support the driveshaft to prevent it from falling or damaging anything.
4. Remove the U-Joint: This is the trickiest part.
* Apply Penetrating Oil: Generously apply penetrating oil to the U-joint cap retaining clips. Let it sit for a while to help loosen them.
* Use a U-Joint Separator: This is the recommended method. Position the separator correctly and carefully press the joint out. Avoid using excessive force.
* (Alternative - Pickle Fork): A pickle fork *can* be used, but it risks damaging the yoke. Use extreme caution if you must use this method.
5. Install the New U-Joint:
* Lubricate: Lightly grease the new U-joint's cap and bearing surfaces.
* Install the caps: Carefully install the new U-joint caps into the yoke.
* Secure the caps: Install the retaining clips and tap them into place using a hammer and punch. Be careful not to damage the clips.
6. Reinstall the Driveshaft: Carefully reinstall the driveshaft, ensuring it's properly seated in both the differential and transfer case (if applicable). Securely tighten all bolts.
7. Torque Specifications: Use a torque wrench to tighten all bolts to the manufacturer's specifications. These specifications are usually found in your vehicle's repair manual.
8. Lower the Vehicle: Carefully lower the vehicle using the jack.
9. Test Drive: After reassembly, carefully test drive the vehicle to check for vibrations or other issues.
Important Considerations:
* Repair Manual: A factory service manual for your 1989 GMC Sierra is highly recommended. It will provide detailed diagrams and torque specifications specific to your truck.
* Professional Help: If you are not comfortable performing this repair yourself, it's best to take your truck to a qualified mechanic. Improperly installed U-joints can lead to serious damage or accidents.
* Driveshaft Balance: After replacing a U-joint, it's a good idea to have the driveshaft balanced to prevent vibrations.
This is a general guide. The specific steps may vary depending on your truck's model and configuration. Always consult a repair manual for your specific vehicle before attempting this repair. Remember safety first!
