Changing Rear Diff Fluid
 

I plan to change the fluid on my '02 EB Expy RWD. what is the recommended oil and weight and capacity?

It depends on what axle you have. It's either the 8.8" or 9.75" and the tag on your driver's door will list a code that you can look up here. Also, there should be a metal tag that's attached to one of the bolts on the rear pan. That small tag will tell you the weight.

I have the 9.75" axle (H6) code. It requires 75w-140 synthetic fluid and I used Mobil 1 brand. It also required the friction modifier additive (even though the Mobil 1 bottle stated no friction modifier was needed) because I had chattering.

Any questions, please ask.

Straight from your owner's manual...

Motorcraft SAE 75W-140 Synthetic Rear Axle Lubricant
2.9-3.1L (5.5-5.8 pints)

It also has the following note which tells you not to change the fluid...

Your vehicle’s rear axle is filled with a synthetic rear axle lubricant and is considered lubricated for life. These lubricants are not to be checked or changed unless a leak is suspected, service is required or the axle has been submerged in water. The axle lubricant should be changed any time the axle has been submerged in water. Add 118 ml (4 oz.) of Additive Friction Modifier C8AZ-19B546-A or equivalent meeting Ford specification EST-M2C118–A for complete refill of Traction-Lok axles. Service refill capacities are determined by filling the rear axle 6 mm to 14 mm (1/4 inch to 9/16 inch) below the bottom of the filler hole.