Iwas having the oil changed and the "tech" showed me a sample of the fluid from the rear diff, it was from mine I watched him dip his finger in and put iton the sheet. The fluid was really black and of course they strongly suggested that they change it for me, I said no. If I am remembering correctly these take a special fluid from Dodge. What I need to know is this; is the fluid dark to begin with? I remember that when I had an International Scout the rear diff fluid was a special kind because of the Posi and it was pretty dark out of the container. The truck isa 1999 2500 V10 4x4. Thanks

 

Diff oil is lighter than motor oil. At least the syn is.

You only need an oil with friction modifier in it if you have an LSD unit. Most all syns have that now. 75w90 is the light duty and 75w140 is the severe duty recommendations for the '01. Just pull the bolts, crack the pumpkin with a screwdriver, and drain. Scrape the RTV off the cover, apply new (all around the bolt holes) and reinstall cover after waiting about 10min (this helps the RTV set on the cover and not the axle housing). Wait about 2-3 hours and refill diff with your choice of fluid.

One tip, wear really old clothes and try not to get any of it on you. It stinks to high heaven and can be a bear to get out.

 

Yeah it's not hard to do. He pretty much stated how to do it above. Just take the cover off to drain it. Once of clean the old gasket off and take a RTV. I use The Right Stuff and make a gasket on it. Make sure to go around all the bolt holes then put it back together. The Right Stuff says to put it backtogther within like 5 minutes or something.


I used to use Royal Purple for the rear and front and still have it in the front but when I put the Auburn LSD in I was told not to use Synthetic so I had the shop put in what they had with the friction modifier. He told me it was Lucas even after telling him I didn't want Synthetic and that it would be fine as it was made for LSD's. I don't know if it's Synthetic or not but so far it works well. I don't know what I will use next time I do it.

BTW here is a DIY on how to do it.
http://pavementsucks.com/tech/diff.php

 

Thanks for the tips. But I would like to know if the new diff fluid is dark or ?? when new. Anybody have an idea?? Again thanks

 

Wow, that's the first time I've ever quoted myself. BTW, that's new oil.

 

If it's black you should probably change it out. It's not hard nor expensive to do.

It shouldn't be black. It should have a light color to it kind of like motor oil only maybe not quite that dark. Atleast what I've used always had. How many miles do you have on it? It sounds like it needs changing.

 

Woudn't hurt to change the front one while you're at it. I like changing mine at the same time.