Rear end & synthetic oil question

[JeffU]

On my last rear diff fluid change I used dino oil and the Mopar additive for posi. I am about to change again and have heard some good things on the forum about synthetic.

Do I still need the additive ?And any brand recommendations ?
Thanks,
Jeff

[jeepdude10000]

doesn't matter what oil u put in, syn or reg u still need additive.
I use valvoline syn.

[Rocketman]

You don't need additive in all diffs. I've been running Mobil 1 75-90 in mine straight up with no issues.

Am I incorrect??

[90xj06]

i have a mix of what ever was in there and synthetic.

[Blkxjkrawler]

there are some synth oils out there that claim to have the friction modifier additive in them but you will have to read the label. My .02, if you change your gear oil regularly, you might save your self a little coin and stick with conventional oil, and a friction modifier. If you dont mind spending, get a high quality synthetic, and add a friction modifier. LS clutch packs are spendy enough that a $10 tube of additive is good investment regardless of what the oil bottle says

[JeffU]

So it is not possible to have to much friction modifier in the differential ? As it may already be in a synthetic.

[90xj06]

is this only in an LSD or in all + how can you tell if you have an LSD if you dont open it? i have a 90.

[langer1]

Look at the sticker in the glove box or a red ring on the fill plug.
You need friction modifier for LSD because it uses friction to drive both wheels.
I really don't see the point of using synthetic which reduces friction when friction is what you need for a LSD.

[MGrobe]

Yeah, the friction modifier is only needed if you have the factory LSD or some other LSD whose instructions instruct its use. So don't use it if you don't have it.

Synthetic is more durable than dino oil so it won't break down as quickly. Not everyone follows the normal maintenance schedule and if it somehow overlooked the synth would last longer and prevent more damage from occuring.

[xjtrailrider]

I set up rear ends and I always recommend Lucas gear lube. 80-90 for the front and 85-140 for the rear. Good stuff.

[tommyr]

I would go synthetic as others are saying & if you have the LSD get the 4oz bottle of friction modifier from the dealer. If your usage is "heavy duty" or "trailer tow", DC specs 75w-140 synthetic. Per FSM Chapter 0 lube & maint.

Personally I would rather spend a couple bucks on Synthetic now for its advantages than have to change noisy pinion and carrier bearings later....

[gregmondro]

Don't mean to bump an old thread, but how much friction modifer do you need to add to a D44 rear end with the limited slip?

[JeffU]

Just buy the Redline lube. It already has the additive. The difference was very noticeable from the previous lube with the Mopar additive. I am running it front and rear.

[mikeny59]

mentioned it before, lsd friction modifier is almost always available at closest GMC dealer, tiny little bottles...

[gregmondro]

Back to my original question. How much of the stuff do I need to put in?