rear diff fluid

**jt_5.7** · 09-17-2009, 02:46 PM

i want to change my fluid but im not sure how could anyone tell me how i would be able to do this

**Greg84** · 09-17-2009, 03:17 PM

My last 3 trucks were like this, not sure what year yours is but its probably the same.

The drain plug is on the bottom of the rear differential, it has a square hole in it so just take a 3/8" ratchet wrench without any socket on it and stick it in the hole to remove the drain plug. There should be a fill plug on the back side of the case that comes out the same way. After all the old fluid is drained, put the bottom plug back in and fill it up from the top hole until the fluid is filled up to that hole. Replace the plug and you're done.

You'll have to check your manual for what fluid to use, I believe I used 75W90 in my half ton and 75w140 in the 2500hd. If you have a limited slip rear differential (real limited slip, not just the G80 locker) you will need an extra bottle of additive for it to work properly too.

Filling it will be a real pain in the ass too, I found taking down the spare tire made it a lot easier to get a funnel in there. Or maybe a little hand pump to fill it up would work good too.

**Crawdaddy** · 09-17-2009, 03:50 PM

If you have a 10-bolt rear (10 rear diff cover bolts) you have to remove the diff cover to drain the fluid. Get a new gasket for it and reinstall the cover. On the passenger side of the pinion near the top will be a 3/8 or 1/2 square-drive plug. Pull it with just a bare ratchet of the appropriate size (well, it's close enough, just make sure you're in the hole all the way) and then fill the diff until the fluid level is even with the bottom edge of the fill plug.