Here's a general outline of the process. Specific details may vary depending on your exact rear axle configuration. Always consult a repair manual specific to your Blazer's rear axle for precise instructions and torque specifications.
1. Preparation:
* Safety First: Wear safety glasses and gloves. Use jack stands to securely support the vehicle.
* Gather Tools: You'll need a variety of tools, including a suitable socket set (metric or SAE depending on your axle), a gear puller (specifically designed for spider gears), a differential bearing separator, a torque wrench, a drain pan, and possibly a punch and hammer.
* Drain the Gear Oil: Completely drain the differential fluid into a suitable container.
2. Differential Removal (If Necessary):
* Depending on your access and comfort level, you might need to remove the entire rear axle housing from the vehicle. This typically involves disconnecting the driveshaft, brake lines, and shocks. Consult your repair manual for specific steps.
3. Differential Case Disassembly:
* Remove the Axle Shafts: Remove the axle shafts (using appropriate tools – potentially a slide hammer) from the differential case.
* Remove the Differential Cover: Carefully remove the differential cover.
* Remove the Ring Gear: This is often done using a ring gear puller. Be careful not to damage the ring gear teeth or the differential case.
* Remove the Pinion Gear: This step may require specialized tools and careful attention to keep the pinion bearings and races from being damaged. This usually involves removing the pinion nut and carefully pulling the pinion gear out. You may need a pinion gear puller.
* Separate the Differential Carrier from the Case: Remove the bolts securing the carrier to the case. The carrier, which holds the spider gears, should now be separated from the case.
4. Spider Gear Removal:
* Remove the Side Gears (Differential Pinions): Use a suitable gear puller designed for this purpose to remove the side gears (differential pinions) from the carrier. They can often be stubborn.
* Remove the Spider Gears: The spider gears are typically held in place by the side gears. Once the side gears are removed, the spider gears should come out relatively easily. However, you may need to gently tap them out with a punch and hammer. Be extremely gentle to avoid damage.
5. Reassembly (In Reverse Order):
* Reassembly is the reverse of disassembly. Pay close attention to the orientation of parts and use the correct amount of differential shims (if present) to ensure proper gear mesh. This is CRITICAL for proper function and longevity. Incorrect shimming can destroy the gears.
* Refill with the correct type and amount of differential gear oil.
Important Notes:
* Shims: The shims between the ring gear and differential carrier are crucial for proper gear mesh. Do not discard them or mix them up. Pay close attention to their positions and thicknesses during disassembly and reassembly. Incorrect shimming will lead to premature wear or gear failure.
* Bearing Races: Inspect the bearing races on the differential carrier and axle shafts for wear or damage. Replace them if necessary.
* Repair Manual: A repair manual specific to your 1975 Chevy Blazer's rear axle is absolutely essential. It will provide detailed instructions, torque specifications, and diagrams that are crucial for successful disassembly and reassembly.
This is a complex procedure with many potential points of failure. Again, if you lack experience working on differentials, it is strongly recommended to have a qualified mechanic perform this repair. Improper disassembly or reassembly can easily lead to costly damage.
