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ORIGINAL: kidsoncoffee

I'm a stick with good ole diff fluid.  That way I know when my seals go bad, and when I need to change them.  Diffs are too darn expensive to take that chance.

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ORIGINAL: P360onBugs

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ORIGINAL: mud_dog450
It's one of those things where if it was better than running gear oil, then the manufactures would run it from the factory.

i tended to agree with you. thats why  i sugessted a mix.  However the logic in this part of your statement is faulty.   Surely you could agree on LOTS of instances where there was a better way and manufacters still did something else.

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ORIGINAL:05fore
as for tech info if your diff is packed full with greae explain to me in technical terms where the grease is going. oh just so you know i have tooken 2 diffs apart both looked brand new and both with grease and not a drop of water or mud in them the bearings especially last alot longer its really quite simple mud and water that will get in your diff and it will will eat your bearings up quicker than anything. however if its packed with grease they will last for eons.

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ORIGINAL: mud_dog450

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ORIGINAL: P360onBugs

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ORIGINAL: mud_dog450
It's one of those things where if it was better than running gear oil, then the manufactures would run it from the factory.

i tended to agree with you. thats why  i sugessted a mix.  However the logic in this part of your statement is faulty.   Surely you could agree on LOTS of instances where there was a better way and manufacters still did something else.

I completely agree with you.  Hence the reason why I stated "It's one of those things"  because, as a motorcycle/ATV mechanic, I see that sort of stuff all the time and wonder why they did it like that instead of like this.

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ORIGINAL:05fore
as for tech info if your diff is packed full with greae explain to me in technical terms where the grease is going. oh just so you know i have tooken 2 diffs apart both looked brand new and both with grease and not a drop of water or mud in them the bearings especially last alot longer its really quite simple mud and water that will get in your diff and it will will eat your bearings up quicker than anything. however if its packed with grease they will last for eons.

Let's look at it another way.  Let's say that a car windshield is one gear surface, the windshield wiper is the other gear surface, and rain is the grease.  When the wiper comes and swipes away the rain, it leaves the windshield bare.

Unless you are literally pressurizing the differential with grease (which wouldn't work because then diff is vented and you would also pop the seals out), then there is nothing in my opinion that guarantees that grease will run between the gear teeth to recoat the gear mating surfaces for their next contact with each other.  I understand that the diff is packed full of grease, but there is nothing inside the differential that is reapplying the grease to the gear teeth mating surfaces.

I agree that the bearings and seals will last a lot longer because the use of grease will help keep mud, water, dirt, whathaveyou out of the diff therefore out of the bearings. 

But based on what I'm aware of and the properties of grease and how a differential works,  I do not see how packing a differential with grease will keep the gear teeth properly lubed at all times. 

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ORIGINAL: CTownForeMan

So where is your technical support mud_dog450?  We have ran greese in differentials for along time.  It's an old trick. 
Manufacturers don't do it strickly because they don't build these things for mud and water.
So riding with a bad seal letting mud and water in there every ride is better than running greese that may let the gears run dry a little bit? 

Nowhere did I say that, or imply it.  Obviously if you have a seal going bad it is wise to replace it.  If damage is done to your diff because you neglected to replace seals, then it is your fault and yours alone.  I am simply stating that it seems much more sensible to replace seals rather than "let the gears run dry a little bit" like I have been trying to explain, and you just stated they do.  

Greese will keep the dirt out which will be killing your bearings.  When the bearings go out this throughs the gears off which wear out the gears more.  So, now the real question is does water and mud lub. better than greese?  As long as greese is pumped i after every ride it will be fine.  Everytime we get back to the trailer we pump some greese in there.  Yes, eventually the greese will be slung out and way from the gears but, by that time we are pumping greese back in there to work their way back in. 

I do agree that grease will keep the dirt out.  But so does a good seal.  Mud will obviously act as an abrasive between the gears and accelerate wear.  Metal to metal contact will accelerate wear as well, which will happen not long after you start driving once the grease is either squeezed out or slung out from the gear teeth.  Does it not worry you that you have to pump more grease into your diff after every ride?  That means that there are voids in your diff and that leaves space for the grease that comes off of the gear teeth to go.  I can assure you that the grease will be removed from the gear teeth and not be replaced the first time the gears go round and round.

On my foreman I drill and tap the differential cap for the greese zerk.  This means when and if the diff. ever goes out it won't be that hard to convert it to greese.  Seals will not last with the punishment we put them through and the mud and dirt will rip apart a differential than greese will. 
Also greese gets worked into the bearings for lubercation.  This is alot better for the bearings than dirt and mud is for them.  I would only recommend this for people who ride mud and water alot.  This is not required for the trail rider with little mud and water riding.  

I do agree that mud and dirt will ruin a diff, but I'm not so sure about which will ruin it first.  Once the grease film is wiped away from the gear teeth, heat can quickly build up in the gears because it does not have the gear oil to help cool it down.  Between the heat and the bare metal to metal contact between the teeth, I'm not sure which would ruin a diff quicker.  All of this can be prevented by properly maintaining the diff by making sure it has fresh gear oil before every ride as well as making sure the seals are in good order and are not leaking.  I'm not saying that just because they don't leak they won't let stuff in.  I know they will let mud and water in even if they are brand new, but making sure it has fresh gear oil prior to each ride will remove most of the stuff the seals may have let in.