Differential Friction Modifier
 

Am going to change gear lube in the rear differential of my 99 2500. It is a limited slip.
My question, is how much to add? The tube I bought has 4oz. In it. Do I put in all 4oz. ?
Thanks!

This depends on the oil you use, and the state of the frictions in your differential.
I suggest that you start without the modifier, then drive some tight figure 8s in a parking lot.
If you get chatter you add one ounce, and try again. Add just enough friction modifier so that the chatter stops.
Too much of it makes the limited slip inefficient, and impairs drivability on slick surfaces.

Thanks Alpine! I'm not going to use synthetic lube.
In the manual I saw 80w90, but I saw a few old threads where they were using 75w140. That has me a little perplexed! You wouldn't happen to know a ballpark figure on how many quarts I might need would you? Thanks!

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If you want to go 75W140 for heavy duty use - go synthetic.(As you see above)

A lot of standard gear oils do already contain friction modifier.

The axle type is on the build sheet sticker under the hood. Or you can ask your dealer to print it for you.
Or use https://www.chrysler.com/hostd/windo...kerPdf.do?vin=

where you enter your VIN right after the = , no spaces, upper case letters.

Thank You Very Much Alpine! I bought the 80-90w, but maybe I'll take it back and get the 75-140w. We do haul a livestock trailer with it!
Thanks for posting the capacities!

Fwiw,

Amsoil severe gear already has the formulation in it for our track lock differentials,and does not require any additives.

It's all I've ever used in all my vehicles, lsd or open

Thanks Tman!

And because a lot of the gear oils already contain the friction modifier I always suggest the figure 8 thing.
If you got the LSD it should work- it was an expensive option.

Thanks Again Alpine!

You're welcome. Amsoil very expensive, but the good part about it is it's designed to be run for about a half a million miles. All the big truckers use it. The only way that you'd have to change it after replacing with amsoil. is if somehow the oil became contaminated either with water or soot

Thanks Again!