supr

I will be coming up on the 15k change on the 4.10 Dana 80 rear end soon. I tow a heavy 5er. Seems like I have read many threads on the issues with Syn lube disabling the limted slip. Futher, where, say, Amsoil straight works gerat for 1 guy, another guy uses it & has issues. It seems that the 90w with friction modifier or perhaps a 75w--140 dino lube is the best solution? Has any bullit proof syn been found that work across the board? Will you not have to change this at he regular intervals anyway because of clutch matreial in the fluid? I believe the syn is about 4x the price of dino lube, so is it worth it? I doubt anyone has ever lost a rear end with the regular stuff if the level is kept up, outside of a defect?
Also, what is the preferred best practice for dong this?
I believe I read NAPA is a good place to buy a new seal?
Confused!

RowJ

Two ways to skin this cat!

Use petroleum oil Gearlubes and change it @ 20,000 to 25,000 if towing heavy. OR, use a good synthetic and go twice as far for twice as much+/-.

Primary advantage of a synthetic is Thermal Stability. If it gets too hot it will still protect and cool down to original (usable) state. If severe conditions or an emergency arise, Synthetics have been known to save major repair bills - sometimes.

I prefer synthetics because...1- Extra insurance against wear & tear, 2- Same cost per mile, 3- 1/2 the maintenance. I do strongly prefer an 80-140 over an 80-90 for heavy working trucks-a bit more protection with no neg. side effect I know of.

Take your pick and change at good regular intervals for your type driving and you'll be in good shape.

RJ

DODGE4X4

Don't forget to get the Mopar Friction Modifier... two Bottles.

supr

What about the limited slip issue, where it may not work with Synthetic?

RustyJC

We've towed a heavy 5th wheel with our truck for probably 90% of the miles since it was purchased. I use Royal Purple synthetic 85W-140 in the Dana 80. The Royal Purple has fricition modifier blended into its formulation, and it works fine for us. The limited slip is functional, and no additional friction modifier was required in our truck....YMMV.

Rusty

Commatoze

It seems that no two LS's are the same. I use Mobil 1 in mine, and found that although the blottle says no additive is necessary, I had to add nearly 2 bottles to the rear to make it slip and not chatter around corners. You'll immediately know after filling if you need it or not. You'll feel the hopping in corners.

RowJ

Manufactures that add the L.S. Additive to their gearlube are putting in an average amount - suitable for most makes. This "one size fits all" may or may not work for us. Since too much can be counter-productive, and expense probably also, you may, or may not need more, depending on the brand you buy.

Not hard to believe that mass produced rear ends may vary from vehicle to vehicle, like stock auto trannys, and different trucks need different amounts of the friction modifier additive. Add in small increments till you get desired results.

RJ

supr

It is my understanding that on L.S. Diffs., each one may be a little differrent on their adjustment. Also, can anyone address the suject of of the L.S. clutch wear being part of th reason for chnging the fluid at 15k, according to the book? Wouldn't Syn. in theory, need to be changed anyway?

rattle_rattle

I changed to RedLine in the differential and did not ad any friction modifier. It works great.

Johnny

I went with AMSOIL in the rear diff and had to use two bottles of friction modifier. Every once in a while I can hear and feel the rear end chatter going around a corner, especially if there's a little water or gravel on the road. Might need to give it just a little more modifier to get it to completely quit.

Shovelhead

I used AMSOIL in my rear diff 'bout 1-1/2 years ago.
No additive, no noise, no chatter.

Ed

kd460

Just to add to it,I use mobil 1 75w-90. I tow a 5th in the summer weekends and such. I change my fluid every year just before towing season. The first time I changed it (after I bought the truck used), I did not need the additive.

This year when I changed it, I needed just under 1 bottle of additive. No noise but did have the grabiness when turning (before I used the additive).

Only add about a 1/2 a bottle at a time, even less if you already have one in and feel like you still need to add more. I used the additive from autozone, can't remeber the name. Good luck, Kevin

BigBlue

I used pennzoil and didn't have to add any modifier in there. Then again, I can deal with a little grabbiness. I like to know that my LSD is working.

DRD

Used Amsoil , had to add 2 bottles of modifier.

rharveysr

When I changed the diff lube in our 2000..I used the Amsoil 75/90 with 2 bottles of the modifier since it has a Mag Hytec cover it takes more lube. It had that bump and grind around corners so I called Amsoil to see what was up. Tech support decided that I needed to change to the 75/140 and the 2 bottles of modifier to make things work..So here come 7 quarts of 75/140 and modifier at no charge.. Still did the same thing bump and grind on the corners.. Again I called tech support for answers as to why even with the modifier it still had issues.
This time I made a suggestion ...if they would send me another order of 75/140 but this time no modifier. I would refill diff. and then go do the figure 8's like your suppose to and then if it did the same thing....I would add the Dodge modifier(2 bottles).
Sure enough with just the 75/140 in the diff..it did the bump and grind..But then I added the Dodge modifier..and the bump and grind is history..
Who know...all I know is that tech support from Amsoil is top notch!

Rick