Tools Needed:

1. 3/8 drive universal 13mm 6 point socket;

This is not a 13mm and a universal joint, the universal must be integrated in the socket to be short enough to fit. Use a good quality unit. The one I used was a 'Mack'.

2. A pump to pump the oil out & pump the new oil in. The one I used was an old Sta-Lube pump. I used different hose configurations to pump oil out of the differential and pump new oil in.

3. 2 qts. synthetic gear oil. I used a 50-50 mix of Redline 75-90wt & 80-140wt. Manual just specs out API 5 or 6 gear oil. The lower viscosity of the synthetic oils made me think even the 80-140wt would be okay, but I mixed with 75-90wt because this would be the more customary differential oil viscosity.

I also added a 150gm tube of Lubro-Moly MoS2 differential additive. I've used this for years in Mercedes rear axles without problems and I like the coating/plating action of the Moly lubricants in high pressure/high shear applications like the differential.

4. Small flashlight/Penlight


Procedure:

1. Get rear end of car up on jack stands with ~4 inches of air between tires & ground.

2. Locate fill plug. Its on driver's side about even in height with the pinion, back about 3 inches from the pinion and facing forward. The rather complicated suspension arrangement with the transverse leaf spring and the big aluminum plate underneath the leaf spring really complicates access.

3. Remove fill plug. The 13mm universal socket on the end of a ~6 inch 3/8 extension will allow access to the fill plug. Poke the socket in to the fill plug between the saddlebag like fuel tank well on the driver's side and the differential. Make sure you get full engagement of the socket on the fill plug; you don't want to mess that hex up! My fill plug was tight; I had to put a cheater on the end of the ratchet to get it cracked loose.

4. Pump oil out. After putting a hose on the suction side of my Sta-Lube pump, I found that I had to transition the hose diameter down to ~1/4-5/16 inch to be able to fish the hose down inside the differential. The smaller hose is easier to manipulate. After pumping the oil out into a pan, I drained the contents of the pan into quart oil bottles to measure the amount recovered. I got about 1.2 to 1.3 qts. Spec is 1.7 qts. I assumed that the level was a bit low. The color of the recovered oil did not look bad, but after 12 years and 128k miles, it was time to retire it from service.

5. Pump new oil in. Mine took pretty close to the 1.7 qts. I've been taught never to over-fill these differentials as it can cause pinion seal leaks. An oil level 1/4 to 3/8 inch below the fill plug hole is quite sufficient. I indicated this with white plastic zip tie bent to a 90° angle at the last 3/4 inch. Poking this in the fill plug hole enabled measurement.

6. Reinstall fill plug. Access is so tough that it is not really possible to get the fill plug started in the threads by hand. I used a leftover piece of heater hose ~4 inches long stuck on the end of the 3/8 extension flipped backwards so the the heater hose fit tight on it. The hole on the heater hose was big enough for the 13mm hex and allowed a little wobble to get the plug threads engaged in the hole. You can't use the universal socket because with the plug backed out of the threaded hole > 3/8 inch, you can't get the socket on the hex, etc. One can't help but wonder occasionally about some aspects of Volvo engineering.