Just a quick question. I read somewhere on this site how to change the rear diff fluid and what fluid to use but now I can't find it. Can someone run me through it real quick and let me know what fluid to use? I have a 1997 B2300 2.3L 5-speed manual with 90,000 miles. Thanks in advance and keep up the great work. This site is very helpful for the do-it-yourselfer.

 

Its prett simple, so here we go. I say this assuming the truck has an 8.8" rear end.

First, you wanna scrape as much dirt off the top of the diff as you can, so you don't knock any into the housing when its open. Then pull the cover off the back of the diff. I always loosen the top bolt off but leave it in, that helps control spills. Once most of the oil has drained you can pull the cover right off. There will be some oil left in the bottom of the pumpkin, try to get as much of that out as you can by "squeegeeing" (if thats a word, lol) it out with a paper rag, or something of the like. Once your satisfied with how much oil you've gotten out, or don't feel you can get anymore, you have to clean the mounting surface on the diff and the diff cover. A wire wheel in a drill works wonders on the cover, and a regular gasket scraper works good on the diff itself. Its a good idea to inspect the shape of your gears, c-clips, clutch paks if its a posi, etc. when changing the oil. Once you've got this all cleaned up, apply a layer of orange silicone to the cover and spread it out so it covers the entire mouting area. Now you're ready to re-install the cover. Once the cover is put back on, you're ready to fill it up. If you're a neat freak, you might want to wipe away any excess silicone. The plug is probably on the front left side, and will likely be a 3/8 drive head. Before you take the plug out, scrape away any dirt that could fall inside. Using an extension on a rachet makes for simple removal. 80W90 should work fine in your truck, and fill it until it starts coming out the fill hole. If the truck has a posi rear end, you will have to add some friction modifier to the oil. You'll want to put that it first, cause if you don't, you won't be able to get it in, since you should stop filling the diff with oil when it starts running out the hole. (The friction modifier will run back out the hole, is what I'm sayin) Put the plug back in and your done! Also while you're doing this, its a good idea to check your rear brake lines for wear or damage, and check that your diff vent is clear and will actually vent.

Hope this helps,

Trevor