Tech Tip- Rear Differential Lubrication

Rear Differential Lubrication

Most of us change our oil and grease the front end steering components of our cars on a regular basis. Some times we change the oil and grease the front end just so we have a record of when these procedures were last performed. You may have, for instance, just purchased a car and you want to make sure the car has been properly maintained. Do you know when the last time your rear differential fluid was changed? If you have no record of the fluid being changed, then it would probably not be a bad assumption that your rear differential fluid needs changing. Many cars out there still have the original fluid in them. Though by now, the fluid has turned into gunk.

The procedure to change your rear differential fluid is no more complicated than changing your oil. Your rear differential is located on the rear axle of your car, where your drive shaft joins the rear axle. The differential housing appears as a ball or bubble directly in the middle of the rear axle. At the base of the differential housing is a drain plug which has a square indentation. The indentation should be the same as a 1/2" drive socket wrench if you have a 1955 or 1956 Thunderbird. For 1957 Thunderbirds, the indentation will be 1/4" square. For 1955 or 1956 Thunderbird owners you can use your 1/2" drive socket wrench to remove the drain plug. 1957 Thunderbird owners will need to obtain a 1/4" square steel rod to remove the drain plug. Your local hardware store should carry the appropriate steel rodding. A piece no longer than one foot with a 90 degree bend in it will do the job.

Located on the top side of your differential is the filler plug. For 1955 and 1956 Thunderbird's, a 5/8" wrench will be needed to remove the filler plug. 1957 Thunderbirds have their filler plug on the left hand side and require the same 1/4" square rod to remove the filler plug as was needed to remove the drain plug. Through this opening is where you will add your new fluid. Your old fluid will drain faster if you remove the filler plug before you begin draining your old fluid. Check your differential for signs of leaks. Adding new fluid will most likely increase any existing leaks. Any existing leaks should be repaired before changing the fluid, otherwise you will be changing your fluid a second time when you repair your rear differential seals.

Once you have drained the old fluid from your rear differential, replace the fluid with gear lube. The fluid weight should be 80W90. Remember to replace the drain plug before you begin refilling. Refill through the filler plug opening on the top or side of the differential. Keep putting the new fluid in your rear differential until the fluid comes out the filler opening. Replace the filler plug. You are now done.

source: CTCC Tech-Tip Manual 1993-1997