My truck has 135,000 on it and id say the gear oil hasnt ever been changed. I'm looking to change the tranny, t-case, front and rear end. I have been hearing some good things about the Royal Purple synthetic gear oil. Is this stuff worth what it costs. I dont care to spend the money if its worth it, but if not what brand do you all recommend? Also what weight should I get? I dont do much towing, but do occasionally tow, sometimes pretty heavy. I also live in East TN, so it gets down in the teens in the winter at night and can touch 95 or so in the summer. Which weight would be the best compromise for these conditions? Thanks.

 

Royal Purple, Amsoil, & Redline are all outstanding synthetic gear lubes.
With occasional towing I would stick with a 70W-90 but with 135k miles flush the hubs to clear the old lube.

 

I was told by a very experienced tranny shop owner to stick with the mineral based 80w90 in the front and rear diff's on these older trucks.

That is what the bearings were designed to work with at the time.

Now say 2002 and newer may be a different story.

just what I was told

 

Has anyone else heard anything about this? Sure dont want to hurt anything.

 

I would use regular gear oil in the front since it doesn't get ran hard, and synthetic in everything else, 75-140 in the rear if you do any heavy towing in the hot weather.