going to run amsoil in rear diff, which one do you guys recomend that run it?

Presuming you're committed to using Amsoil; the Severe Gear.

If you never tow, the 75w-90.
If you always tow heavy, the 140.
The best compromise is the 75w-110.

so if i want to flush it, how much fluid does it take?

Go with the Amsoil 110 ! If your going to re-use the stock cover you will need 4 quarts (min.). I would pull the cover and hose the diff out with some disc brake spray cleaner to get rid of any shavings and to check the ring and pinion teeth.

Nice rig !

Go with the Amsoil 110 ! If your going to re-use the stock cover you will need 4 quarts (min.). I would pull the cover and hose the diff out with some disc brake spray cleaner to get rid of any shavings and to check the ring and pinion teeth.

Nice rig !
thanks same to you. havent pulled the cover on this one, does it have a reusable gasket or just some rtv or go buy one?

Agree with dnewton on the recommendations. Hold off cleaning with brake cleaner. If I remember right, it will not do any favors to the gear lube. Let me get the specifics and get back to you. Heard it at a meeting but for the life of me can't remember the exact reason. If someone else knows, chime in or I'll get back tomorrow.

Agree with dnewton on the recommendations. Hold off cleaning with brake cleaner. If I remember right, it will not do any favors to the gear lube. Let me get the specifics and get back to you. Heard it at a meeting but for the life of me can't remember the exact reason. If someone else knows, chime in or I'll get back tomorrow.
ill wait, appreciate it, keep me posted then i will order the lube from you guys.

I went with the Severe Gear 75W/90 in my dually since I have a Mag-Hytec cover and 7.5 quarts in it. I used 3.5 quarts of the 75W110 in the wife's 2500HD since I kept the stock cover. Regarding the cleaning, I poured about a half a quart of left over gear lube from the previous lube change with the cover off and the drain plug out and let it run out to drain some of the residual metallic film from the bottom of the case.

The spray brake cleaner is used to flush stuff to the bottom of the diff housing where you can wipe it out with a rag (IE. metal shavings). It also flushes the gear oil off so you can inspect the ring and pinion closely. Whatever you don't soak/ wipe out of tyhe bottom of the diff housing with the rags will evaporate in a few min. No harm to the gear oil, cause there is none in the diff.
If your going to use the stock cover again you can use RTV to seal it up or use a gasket, it's up to you.
I really like the syn. gear oils for trucks that will see mainly road use and the oil will be in there for awhile. If your in and out of water a lot use the cheapest dino stuff and drain it often cause you WILL have water in the oil and that will do more damage than anything else.

I cleaned mine up with starting fluid, the cheapest no residue answer. I used 75-140w. Good to go for 100k.

thanks guys, you find anything Heath?

If your in and out of water a lot use the cheapest dino stuff and drain it often cause you WILL have water in the oil and that will do more damage than anything else.

What about using the Universal Synthetic Marine Gear Lube SAE 75W/80W-90 (AGM) if you are in and out of the water a lot with it?

Where will the water get in? Vent line? Anyone know how high the vent line is?

Most of the water will get in through the axle seals by the bearings, past wore pinion seals, and sometimes by bent lips on diff covers. A occasional mud puddle won't hurt anything but creeks ,mud pits,standing water,etc. is trouble. Water in through the vent tube (if the factory tube is in place) is usually not a big problem as they are high on the bottom of the bed. We run our trail trucks through water quite a bit and even with new seals you will get some water after a few long days on the trail. Some of the hard core guys will drain diff's a couple times a month to prevent bearing failures.
I have no experience with the Marine grade stuff.

Ref: Staring fluid will work for flushing out a diff. I have even used a big bottle Zippo lighter fluid. Anything quick evaporating petrol base fluid will probably work. You only really need to flush one out once to get rid of the factory break in stuff it's not a really big deal.

Around how many miles would it be good to swap out the rear diff oil??? I already bought the Mag-Hytec but am waiting until I put some more miles on my LMM (600miles)... And which Amsoil oil product will work in conjuction with G80 locking differential???

Amsoil Severe Gear 75W-90. 75W-110 or 75W-140 if you tow alot (110) or often tow heavy (140). I would change after the first 500 miles. Your diff is probably low from the factory. I ended up adding some slip-lock differential additive after I did my change. I noticed some periodic noise from the back so I added the additive, after adding it no more noise - YMMV. While you're doing the change you might as well change the fluid in the front too (2qts 75w-90).

600 miles is good. You dont need any additive with the G80.

Amsoil Severe Gear 75W-90. 75W-110 or 75W-140 if you tow alot (110) or often tow heavy (140). I would change after the first 500 miles. Your diff is probably low from the factory. I ended up adding some slip-lock differential additive after I did my change. I noticed some periodic noise from the back so I added the additive, after adding it no more noise - YMMV. While you're doing the change you might as well change the fluid in the front too (2qts 75w-90).

How much would I be spending on the Amsoil Severe Gear 75W-90 and who would I be able to purchase it from??? I do tow a 10,000lb trailer maybe 2-5 times a month but not full, maybe 5,000lbs???

I'll send you numbers to look at.
Heath

Just got my response I was looking for on the brake cleaner. I called tech support twice and got two different answers.
ONe, the residue can dilute the gear lube and decrease it's viscosity. With the little that's there, I didn't buy into this all that much.
Second, the residue could break down the additives. The head guy of the gear lubes just emailed me back and confirmed that these cleaners do absorb into the metal and can break down the anti-foam additives, which if happens, can introduce air bubbles at points of contact. Air is compressible and you get metal to metal contact. How much it takes for this to happen is hard to say. To avoid any chance, use some extra gear lube or maybe a cheap version to do a little cleaning.