This is just a data point to share, nothing earth-shattering but perhaps of interest. Vehicle is a 2007 Dodge Ram 2500 Mega Cab 4WD with Cummins TD. At 140 K miles, it was time to change the front and rear axle gear oils; it tows a heavy trailer some and the miles were getting up there. Changed the gear oil to 75W90 Mobile 1 full synthetic gear oil and was pleased and more than a bit surprised at the biiiig reduction of running noise and vibration.

This happens running on level ground, upgrade, and downgrade. Downgrade with the engine coasting at 75 or 80 mph, the truck towing is soo quiet now; the dull roaring is not there anymore. Going up a mountain grade at lower speed, the same happens, and low level vibrations when going up a steep grade is really down. And on the WV Turnpike, going down the gorge from Beckley to Charleston, the axle bearing noise on the tight curves is all gone. And it is significantly smoother from a seat-of-the-pants vibration standpoint all the time.

Due to the symptoms, I think the biggest noise/vibration reduction is in the rear axle bearings, and perhaps the pinion bearings. I expect the gear noise reduction is less... but I can actually hear some rear gear whine now with the other noise so reduced. And after 400 continuous miles today at interstate speeds towing a 2 ton enclosed trailer, the cast AL rear wheels are a LOT cooler than they used to be; that relates to the rear axle bearing being better lubed, and goes with the quieter and smooter operation.

Overall, it has been an eye-opener. I've used Mobil 1 engine oils for a few decades with impressive results, and in trannies. But this is the first time I have had crazy-good results in a live axle. BTW, the gear oil in there before was the factory original; the owner's manaul says to use GL-5 75W90 synthetic or equivalent; I suspect the factory used the 'or equivalent' stuff!

My Challenger and the '62 Dart are getting this right away. I am anxious to see if the Dart in particular improves anything like this.

Interesting and surprising. Will be cool to see what happens with the 60s vehicles...

Lou

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Home of Slant6-powered fun machines since 1988

BTW, I changed the '62 Dart rear gear oil this weekend... could not tell a definite difference on a short drive. But the engine noise through the floorboards is the big source of noise so would mask any changes.

One other item noticed: When suctioning out the old juice, most of it was pretty translucent, but the bottom pint or so was reeeeally dark. So work to get that old stuff out that is way down in the bottom.