i use majestik in my diffs...its pretty expensive, but it is really good oil. my neighbor (practically a mechanic) recommended it to me. its pretty much sold in all the specialty differential shops and high end automotive stores.

 

I have used Royal Purple in the past and I have no complaints. I have been partial to Amsoil in the past, but I just switched to Lucas Full Synthetic after talking to my brother in law who is a chemical engineer from MIT that works for Lucas. I am interested to see how this stuff holds up. I changed my tranny and transfer case fluid too. Only thing I can say for sure is that my tranny shifts like butter.

 

if you were racing or rock climbing or some other extreme type of 4 wheeling i might consider an extreme use oil.the standard petroleum based 80/90 gear oil specified for your vehicle is more than adequate,there are millions of trucks running the road with stock oil.unless you just want a high end oil and that is your preference.keep your fluids changed/topped off as per manufacturer and your truck/car will last well beyond its predicted lifespan.

 

FWIW, this is the best answer to this thread so far :thumbsup:

 

I run Amsoil synthetic severe gear 75w-80 in my diffs. Its expensive but its worth it for me.
Any good 75w-90 or 80w-90 gear oil will do you fine. Redline mt90 is a great gear lube!

 

Ok I just want to give an update. I am not so sure about Lucas synthetic gear oil. The tranny does not shift as smoothly as I would like. When the transmission is cold (about 50 degrees outside) it kind of catches a bit in 2nd and 3rd. Once it is warmed up it does shift just fine. This isnt a big deal, but my tranny has always shifted so smoothly so to me it gets on my nerves. I think this weekend I am going to take the fluid out. Only issue is no one locally sells Amsoil or Redline MT90. I have never tried Redline but I keep hearing that its good stuff so I might give it a shot. The only stuff I can find locally is royal purple. So I might have to go that route because I really want the Lucas oil out of my tranny.

 

Since we're on the subject here, and I dont mean to hijack your thread 1baddtoy, but are there any good how-to guides for doing a rear-diff / tranny oil change on a '90 4x4 (22RE) on here? I tried searching but didn't really find any step-by-step guides on it. Thankee

 

There really isnt much to say..

Grab a 24mm socket and a 2ft breaker bar. Make sure you remove the fill plugs first. You don't want to drain the fluid and realize you can't add any.. (you could use the diff breather and shifter holes in a pinch).

Jack the front of the truck up (helps drain rear diff oil), drain oil. Lower truck till its level, fill with proper oil till it flows out the fill hole, tighten (but not too tight!) the fill plug and you're done.

No biggie

 

That covered all my questions... now to decide what fluid I'm gonna use. Thanks Jay!

 

Its the same method with the diffs tranny and t-case Just make sure you get the correct fluid for all.
Also, a hand pump helps when doing the tranny and t-case. Space is limited, on my truck I have a body lift so there is more room. But on my old ladys stock 4runner, I couldnt get my oil bottles high enough to empty them into the tranny and t-case..

I just went and got a $10 hand pump from the parts store.

And to the O.P Make sure you follow the proper break in procedure for new gears!