If you lay under the truck in front of the rear end were the drive shaft hooks up to it, on the left side of the housing there will be a plug. It may be covered with dirt or grease , clean , and then remove it. put gear oil in there.
read the manual
The rear differential fluid goes directly into the rear differential. There is normally an inset plug that has a square drive on it that accepts a 3/8" ratchet or ratchet extension. Remove this plug. If fluid comes out, you do not need to add any. If no fluid comes out, add enough of the fluid recommended by your vehicle manufacturer (normally 80/90 gear lube, but not always) where you took out the plug, until it starts to seep out the plug hole. Replace the plug and you're finished.
Look at the rear differential housing - you will see two plugs in the housing an upper and a lower. Loosen the upper plug - if fluid runs out of it you have sufficient fluid - if not - add fluid until it just starts running out - then replace plug.
The rear differential is a part of the power train, not a part of the suspension on a vehicle. It is the suspension system you need to be investigating on your vehicle. You more than likely have a broken spring.
To change differential fluid on a 1997 CR-V the vehicle needs to be lifted up to reach the rear differential. Find the drain plug located on the underside of the unit. Pull the plug and drain the fluid, when done place the plug back add fluid into the fill hole which is located topside of the differential.
To fill the rear end (differential) with fluid, locate the fill plug, usually found on the side of the differential housing. Use a suitable fluid pump or funnel to add the recommended differential oil until it reaches the fill hole, typically until it starts to seep out slightly. Always refer to your vehicle's owner manual for specific fluid types and capacities.
To check the rear differential fluid level on a Mercedes-Benz 190E, first, ensure the vehicle is on level ground. Locate the fill plug on the differential housing, typically found on the side. Remove the fill plug using a wrench; the fluid level should be just below the plug opening. If fluid seeps out when you remove the plug, the level is adequate; if not, you may need to add the appropriate differential fluid until it reaches the correct level.
To add oil to the rear axle of a 2000 Oldsmobile Bravada, first locate the rear differential cover. Remove the fill plug, which is usually located on the side of the differential, using a socket or wrench. Using a fluid pump or a squeeze bottle, add the appropriate differential oil until it reaches the bottom of the fill hole. Reinstall the fill plug securely after adding the oil.
On the upper right (passenger for a left hand drive vehicle) side of the differential, there's a plug. IIRC, you need a 3/8" drive ratchet to remove it. That's where you add your diff fluid.
go to a GM dealer and they have a limited slip additive that you add to your rear end fluid.
In a 1997 Ford Aerostar ( REAR differential ) With the 7.5 " ring gear ( 3.5 U.S. pints ) With the 8.8 " ring gear ( 5.0 ) * traction lok , add 4 ounces of friction modifier
Assumeing you are at the rear of your van, if you crawl under the rear bumper you will see the rear axil, the center of that axil in the differential(round part)you should see a bolt or (plug) towards the top left side facing fprward the vehical this is where you can add differential fluid you want to fill it just below the leval of the hole.....