Journier

in the manual it says, use straight 90 weight oil. didnt see anything about limited slip additive :/

can i use sae 80-90 weight oil in the axle?

its a 99 3500, but im not sure which axle it has :/ and what oil i can use, i have 80-90 weight oil from another rear axle oil change.

thanks,
al
edit, accidentally put into wrong forum

apache

Your diff cover should have a tin tag attached by one of the cover bolts that will state its limited slip or?? you might also look at the built sheet sticker under the hood on 99?? it typically will show gear ratios and all xtra equpt added.

TRCM

If it's not limited slip, it won't hurt to add it. if it is, and you don't add it, it wil hurt you on down the road.

crobtex

I used Mobil1 75w90 and used the additive because it's suppose to be required.

Captain

i have a dana 80 rear witch is what all 3500's have i think. From what I remember it was suggested to use 75-140 synthetic in the rear. And 4oz of friction modifer per 3quarts of oil if you have a posi. Your sticker under the hood or in the glovebox should tell you if you have a limited slip rear.

crobtex

I stand corrected.....I did use 75-140.

infidel

It all depends on the oil you use and the wear on the clutch packs. Many oils have modifier added, some have none. Best to add a little at a time till the diff is quiet on turns.

I've seen microscopic pictures of friction modifiers with an explanation of how they work, sort of cool. The modifier looks like a tadpole that buries it's head in the clutch material, the "tail" acts as a lube allowing slippage until a certain amount force on it is achieved then the modifier is pulled out by the tail allowing the clutch to grab.

Journier

thanks for the info guys, just got home going outside right now to check if its limited slip etc.

TRCM

Exactly, and if it isn't a limited slip, it won't hurt the open diff. it will cost more tho. i use it in my locked rear end to cut down on the clicking noise. Got tired of people teling my truck was broke.

turbo thom

Now you done got me real confused. Why put friction modifier in a open diff? You say it won't hurt, but what's the use?

Tadpoles huh? Now that's what I would call a bad tad. To sacrifice his tail for a little slip.

And I think the rear diff calls for 75W-90 synthetic unless towing heavy. Then go to the 75W-140. I ran the 75W-90 for eight years then 2 years ago I changed to the 140. Still I use the modifier, even with the Amsoil. I've been told it's not necessary but I found I needed it. My rear end has 331 on it towing a 15K Teton and other trailers and all I've done is change fluid.

Not to start a fight but the Amsoil is hard to beat for our trucks.

..Preston..

TRCM

I said if it doesn't need it, it won't hurt it. if it does need it, but you aren't sure, it will be in there.

I use it in my locked rear end because it cuts down on the clicking noise from the locker when I turn.

Basically, if you put it in there, you are covered...even if it doesn't need it.

You can tell real easily tho when you remove the diff cover to drain it. if it is a limited slip, you will see the clutches...if it is only 4 gears and a cross pin, it is open and doesn't need the additive.