I have a 2004 3500 crew cab w/dmax and allison. 75% of the time the truck is being used for pulling between 6000 and 10000 pounds. The rest of the time the truck is used just as a normal passenger vehicle. Is there a down side to using 75W-140 lube in the rear diff? Do I use the same in the front or stick w/the 75W-90? I live in Wisconsin and don't use the truck that much in the dead of winter but it still gets some use when it's pretty cold....both with and without a trailer. Any help would be great. Thanks

I'd like to know too. I live in California and don't have the cold temps but truck is mostly used for pulling my fifth wheel that weighs about 9,000lbs. I have been considering the same weight range gear oil.

I have used 80/140 syn. and Mobil 1 75/90 and found the 75/90 performed much better even towing in the heat. Much less metal on the magnet and much less metal flake in the oil.

I have used 80/140 syn. and Mobil 1 75/90 and found the 75/90 performed much better even towing in the heat. Much less metal on the magnet and much less metal flake in the oil.

I think this is more a issue of break in and oil brand matbe than anything else. In hot climates in heavy towing 85w140 (or 75w140) is a better choice and I have used it for years with no problems. 85w140 is a bit stiff in cold weather though. My old JD has 3 gallons of it in gear case and you cannot really use it much below zero unless you switch to 80w90 in it.

I've had Royal Purple 75-140 in the front and rear diff's for about 50K and have not had and problems. I checked the magnet in the rear diff and had virtually no metal. I have driven my truck at -5 deg F and all seemed ok.

Well, 75% of the time towing would probably qualify as "heavy duty", which would them make you a candidate for using 75w-140. But, living in Wisconsin might negate that somewhat (although, the 75 in 75w-140 is what the oil's weight will be when it's cold, so it really shouldn't mater all that much).

Unless the front axle on the 04 is different then the 02 -- which I doubt -- I definitely wouldn't use that weight oil up their. My manual says only the thinner weight oil should be used, and doesn't even list an application for 75w-140 in the front.

Either way, I'd opt for a full synthetic oil. That's a wise choice if you're going to replace the fluid anyway.

I would like to know if it's possible to use 2 qts of 75/90 and 2 qts of 75/140. Same brand syn. Anybody know if it's possible or would there be any benefit in doing it that way?????http://www.dieselplace.com/forum/smileys/Geek.gif

I have mixed weights before and nothing blew up but most oil specialists would probably tell you not to mix weights. Using the same brands should help though I would think.

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<TD id=HB_Focus_Element vAlign=top width="100%" background="" height=250 UNABLE="off">I just changed the real axle oil yesterday. I used 85w-140 Amsoil. I got four quarts and due to me spilling some I had to top off with 80W-90 Pennozoil . I only used 1/2 quart of the Pennzoil to top off. I hope it will be ok. I have only moved the truck a few feet off the ramps it was on. I need a better way to get the oil in the rear end. I used a funnel with a long tube but over ran it a few times. </TD></TR>
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I use a piece of 3/8" id fuel line hose over the nipple on a oil bottle to reach those difficult places. On my truck, it is the front differentail and tranfercase fill port. Edited by: snoman

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<TD id=HB_Focus_Element vAlign=top width="100%" background="" height=250 UNABLE="off">I need a better way to get the oil in the rear end. I used a funnel with a long tube but over ran it a few times.</TD></TR>
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I use a 1' hose that screws on the oil bottle. I picked it up at the local car parts store. That works real good. When doing the rear differential, I Also lower the spare tire. That gives you plenty of room to get the oil in.Edited by: JohnnyO

I use a piece of 3/8" id fuel line hose over the nipple on a oil bottle to reach those difficult places. On my truck, it is the front differentail and tranfercase fill port.


Thats exactly what I do and squeeze the stuff in. Transfer the top to the next full bottle and repeat. Take the partials and last drop em into 1 bottle to top off.


Blake