How much gear oil will I need for the front and rear diff? I'm going to take off the covers and clean the inside, the put them back on and refill. Front is 10 bolt, rear is 14 bolt.

Would it make any sense to use synthetic gear oil? I'll probably be changing it every year or two anyway, and synthetic is pretty expensive.

Do I need special oil or some additive for the rear? The glovebox sticker says the rear is a locking diff.

10bolt is around 2 quarts I think and a 14 bolt close to a gallon 3.7 ish

Check this site out. All the info you need

http://www.amsoil.com/scripts/runisa.dll?amsoiloaf:index

Great resource!

80W90 or 85W90 synthetic...front is about 2 and rear is about 3-4 IIRC

I run synthetic due to lower friction which must help in some way.

synthetic is better for colder climates, as it will slip better. limited slip should have gm additive in with the gear oil for the clutch's. I called a gm dealer once to ask if the additive should be added when using synthetic. they said probably not as the newer ones come with straight synthetic . i still put the stuff in cause they wern't positive

Thank you all for your input!

The amsoil site gives quantities by the size of the ring gear, but I don't know the ring gear sizes ... However, it seems I'd have to buy 7 quarts.

A quart of synthetic costs about $15, that would be $105! Dino is maybe 1/2 that. Will synthetic pay out, or does it have such a great advantage that it's worthwhile? Do you keep it in longer?


PS: Hmm, amsoil isn't that expensive. I've got a dealer less than 5 miles from here, I'll check that out.

PPS: How much is a pint? Do they mean a "US dry pint" or some other kind of pint?

I don't know, I don't put a lot of money into my rear axle. What's more, it never gets a fluid change unless it all leaks out for some reason and the stupid thing starts howling... Then I'll grab a couple bottles of 80/90 gear oil at walmart and dump 'em in there. Never cost me more than like $10 to fill my rear axle. In my opinion, it's just not like an engine which needs lots of fluid changes. I say if it stays full don't touch it... Maybe every 100K or so, that's it. And expensive fluid? Forget it...

EDIT: I just reread the initial post and notice the locking diff. Disregard, that needs proper fluids and also to be changed every now and then... Carry on...

I don't know, I don't put a lot of money into my rear axle.


Well, it's front and rear, and if they are broken, I have a problem. So I figure changing the diff oil every year or two, depending on how much I drive, is better than breaking them. And in this case, I didn't open the diffs since I got the truck, so there could be stuff in there that I better take out.


Maybe every 100K or so, that's it. And expensive fluid? Forget it...


Amsoil says 100k normal, 50k under severe conditions. That would be like every two or three years or 4/6. Anyway, I'm hoping that I might improve mileage, and if synthetic gear oil helps it, it may pay out.


EDIT: I just reread the initial post and notice the locking diff. Disregard, that needs proper fluids and also to be changed every now and then... Carry on...

Lol, ok, but do I need something special? I know that limited slip differentials quit limiting the slip when they don't get their additives or when the clutches are worn out --- like the one on the Tahoe did. But I was told a locking diff is different, and it still seems to work.

But I don't know _how_ the locking diffs work --- I don't want to break the locking feature by using the wrong oil.

If you're looking at amsoil, the slip additive is already in the product. Use the severe gear 75W-90. Synthetics gear lubes do help them run cooler and the interval mentioned above is correct.
The price mentioned above is a little off...check around:)

I switched to synthetic gear oil in my L9000. The diffs run about 50 degrees cooler than with mineral gear oil. Also with my F350 I noticed with synthetic there is less rolling resistance with the hubs locked in. The front axle in the F350 is a Dana 60. Then again your mileage may vary.

Yeah, I know, I know, the whole "regular maintenance prevents costly failures" speech... :p: No offense intended, it's just that on a plain open diff though I don't even really see a reason to touch it probably during the life of the truck unless it runs out of fluid... At least not on something this old. I mean if I had a really expensive vehicle maybe, but this thing I've got will keep working fine as long as it has oil in it. Not that I can really recommend my maintenance methods regarding the rear axle as it's technically not right, but that's just how I do it on my truck, I'm broke, lazy, and would rather spend the money on something that's more likely to give me problems.

That "locking rear end" is probably a G-80 gov lock. Basically what it does is it locks up when the speeds of the two axles is different by more than ~100 rpm, and it doesn't lock when the vehicle speed is over a certain speed (I think it is 25 mph). Pretty nice setup but I don't think it is known for being extrordinarily strong. I don't think it requires any special additives like a limited slip diff, which will chatter around corners without the friction modifiers, but don't quote me on that.