Mobil 1 gear lube question

I was wondering if any of you folks who use the Mobil 1 synthetics know what gear lube I should use for my 98 K1500. My manual says to use 80W-90, GL-5
but Mobil 1 does not have a synthetic for that. Is the 75W-90 ok to use or do I use the conventional Mobilube HD Plus 80W-90 instead?
Dave
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dcbryan wrote:

GM recommand 80w90s unless in a very cold cilamte for the front diff on 88 and new trucks because it 2wd mode the front spider gears are always spinning as only one axle decouples and the the other spins off in the spiders to prevent drive shaft from turning and the 80w90 provide a little thicker portective film for them. You could use it but personally I would not bother. Better off with regular lube changes for it every 20 or 30K if you want it to last a long time rather than less frequent changes with a more expensive oil and any gain in MPG from it in front axle would be minute. I would use it in rear axle though if you wanted too and do not forget to change Tcase fluid either.
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I've used the Mobil 1 Gear lube you mention in my '97 Tahoe for quite a few years. You will not have a problem with this lube in either front, or rear axles, even if you have a rear limited slip variety, which I myself do.
A multi-weight Lube such as this, and also motor oils too, become whatever weight they need to be according to weather and/or operating temps.
For example, a 5W30 Oil is 5 weight upon start up, but as an engine comes to operating temps, the oil then acts/becomes a 30W oil. Same with 75W90 Axle Lube.
A synthetic Gear Lube such as Mobil 1 will exceed specs of all conventional gear lubes, have better additives, offer better protection, and lubrication in temperature extremes, both extreme cold, and hot, and I highly recommend the full synthetic gear lubes if you also tow.
Extreme cold can be a just as big a killer on axles as extreme heat.
I'm talking International Falls, MN sort of cold, where in winter it might be a "warm" -20F day, and your conventional Axle Lube is like Vaseline for the first 10 miles of driving. It is under these brutal conditions that conventional lubes do a poor job of protecting your axles from premature wear/failure. Mark D.
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Mark D wrote:

GM spec'd it for 80w90 for the reasons I stated earlier and it is not meant that 75w90 covers it. It is acceptable to use it in a cold climated but not recommand in a warmer one in the front axle. GM spec'd it, not me. I have a 2000 K3500 that I have had since new and it plows snow too and it has 75w90 in rear and 80w90 in front (both dino oil) and they get changed once a year along with Tcase fluid.
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Snoman, Don't quote me on this, but I understand that newer GM Trucks/SUVs are already coming from the factory with full synthetic gear lubes installed. The GM Parts Counter folks could probably confirm this.
One fallicy/belief I had many many years ago, was that you never were supposed to completely change out gear fluids, and was supposed to only just top them off.
I probably got this dumb idea working-servicing Semi-Tractors, where it would be prohibitly expensive for a company to constantly be periodically changing out gear lubes on their large fleets of trucks.
I understand now, how untrue that is, and it actually wouldn't hurt a thing if you hypothetically changed out axle lubes every 3,000 miles, but as we all know, this would be an excessive waste of money, and is unnecessary to do.
Typically, what I've done over the years with many of my vehicles, when I felt it was time to change-refresh Gear Lubes, was to just use an inexpensive Fluid Suction Gun, with a 2' Hose attached to empty Axles, and have a Oil Drain Pan nearby to empty the old Lube into. Takes only about 5 minutes per Axle to do, and another 5, or so, to refill.
While I know I don't get every last drop of Lube out in an axle, which I feel is not that important/critical, It saved me the hassle of ripping off Axle Covers, and worrying about the chance of minor leakage down the road. Mark
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Mark D wrote:

    What your doing is leaving all the crud & debris in the bottom well in the center section. Then it mixxes with the new lube/oil and does the same damage it was doing before hand.
    A paper gasket, and tube of black RTV don't cost very much at all. Charles Why people will risk ruining a few houndred in parts when a extra 15 minutes, and a extra $15 dollars is at stake, is beyound me.
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Charles Bendig wrote:

No need to remove cover completely and clean it out because the more you expose it the greater the chance of dust and grit getting in there. Been doing it without completly removing cover for over 30 years and I have not had any problems.
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TheSnoMan wrote:

    Following your logic, you could justify the married woman I was sleeping with for 2 years. Charles
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What your doing is leaving all the crud & debris in the bottom well in the center section. Then it mixxes with the new lube/oil and does the same damage it was doing before hand. A paper gasket, and tube of black RTV don't cost very much at all. Charles Why people will risk ruining a few houndred in parts when a extra 15 minutes, and a extra $15 dollars is at stake, is beyound me. ====================================== I doubt that very much.
I forgot to mention that I do drive the truck till fully warmed up before I change lube, the same way you supposed to do with Motor Oil changes.
Doubtful that I'm leaving much, if any debris at all, and I do make sure I take the time to get the Suction Hose to the lowest area in the Differential. Mark
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Mark D wrote:

    You might be suprized at how much is in there. If you leave a diff set long enough (such as a winter only truck) 97% of the large crud will be in the well. Most GM Center Section have a well that goes up under the pionion to the seal area. Ask my business partner what happenes when you don't inspect that well after changing broken spider gears.
     Charles
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Pull the diff. cover and take a look if it's never been off. This way you can clean the magnet. My OEM lube was black n' crappy at 40k, glad I serviced it then as the lube was breaking down. Just bought the truck BTW at that mileage. I glued on the gasket to the cover & greased the other side for no stick so when I took a look at 60k all was clean & happy with the M1 onboard. Refilled w/M1 and now I will not drain it untill 100k, just level / color checks along the way. Colors good, it stays in. Only the 30 series trucks get synth. in the diff's OEM, the rest get regular dino. '99 Yukon
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find your self an AmsOil dealer. Much superior product that Mobil 1 any day of the year
dcbryan wrote:

synthetics know what

use 80W-90, GL-5

75W-90 ok to use or

GM recommand 80w90s unless in a very cold cilamte for the front diff on 88 and new trucks because it 2wd mode the front spider gears are always spinning as only one axle decouples and the the other spins off in the spiders to prevent drive shaft from turning and the 80w90 provide a little thicker portective film for them. You could use it but personally I would not bother. Better off with regular lube changes for it every 20 or 30K if you want it to last a long time rather than less frequent changes with a more expensive oil and any gain in MPG from it in front axle would be minute. I would use it in rear axle though if you wanted too and do not forget to change Tcase fluid either.
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