How much angle is too much angle for the rear driveshaft?

Wow! This video is great! I didn't know it existed, I need to embed it on our website somewhere. People are always worried about lubrication when they rotate their pinion. At first glance it makes sense to worry. We try to always assure people that the ring gear slings oil all over the place, "like a tire slinging mud" is what I usually say. But this video really shows how it is much more than a gentle splash, no way the oil won't get where it needs to go, unless of course there's not the right amount in there. The location of the fill plug changes, that's the thing that gets most people. That and just never checking or changing your diff fluid in the first place.

One other thing I'd like to add to the conversation is that people will sometimes say something like "I had my pinion pointed 15 degrees up and my pinion bearing went bad." The logic, which seems legit at on its surface is that there is cause: more angle and effect: bad bearing. But the reason their pinion bearing went bad before the other bearings in the diff is because of gearing. The fact that it happened X number of months after rotating the pinion is just coincidence. If you are running 4.10 gears your pinion is rotating 4.10 more times than your axles. This means that pinion bearing is spinning both 4.10 times as many times but also 4.10 times as fast. For some fun math (approximate numbers), lets say you have 150,000 miles on your Jeep with 4.10 gears. Over the life of that jeep your tires/axles/and side bearings in your differential have made 375,000,000 rotations. With 4.10 gears your pinion bearing will have made 1,537,500,000 rotations! And remember it's always spinning 4.10 as fast as the side bearings too! If a pinion bearing ever makes it to 150,000 miles it is a miracle of modern manufacturing and science that something that you can buy for $20 can ever last for 1.5 billion rotations.

Where are you coming up with this math? 375,000,000 rotations of the tires/axles/side bearings would indicate 2500 revolutions per mile at 150,000 miles. A 27" tire is 766 revs per mile.

I don't agree that the pinion spinning x times faster than anything else is a problem or contributing to any sort of failure. Sure, it spins faster than the carrier bearings and wheel bearings. That's all it spins faster than. The t-case input/output bearings and the transmission output bearing all spin the same amount. All of that stuff spins even faster with a regear but yet no one seems to be having problems with them (not including the pinion bearings in the discussion because they are usually replaced at regear time).

If one bearing spinning 3-5x vs another bearing is an issue, then we have to have a defined number of revolutions until bearing death before we can attribute that as the cause. Otherwise, with this logic, we could say exactly how long everything else will last, but we don't know that. The truth is we don't know any of that and we don't know that "being a pinion bearing" caused the guy's pinion bearing to fail. It's all being lubed constantly and experiences very little to no wear per revolution so I don't think we can really say "well it's a pinion bearing, that's why it failed." If we could, then we could also say all the stock Jeeps that shipped on 4.10s will expect to replace their bearing before all the Jeeps with 3.07s have to. Real world, we don't see that.

But back to the math. Call it 31" tires for an average tire size. Random tire on tirerack at 245/75R16 (stock Rubi) is spec'd to roll 683 revs per mile. 150,000 x 683 is 102,450,000 tire/wheel bearing/carrier bearing revolutions. Multiply that by 4.10 and you arrive at 420,045,000 revolutions for those 150,000 miles.

Let's look at an engine instead. Stock Rubi (6-speed) turns about 2350 rpm at 60 mph (used because 1 mile = 1 minute at 60). 2350 x 150,000 = 352,500,000 engine revs. Obviously we know of plenty engines going far far beyond 150,000 miles. Do revolutions really even matter past this point? Different style of bearing than a tapered diff bearing but still, moving parts nonetheless.

I don't think the guy angling his axle up killed his bearings, but I also don't think his pinion spinning faster than the carrier did either. I think the important part is that we can't predict longevity of any bearing really, many will last many miles despite their revs/speeds and some will be flawed and die due to their manufacturing or other factors like lack of lubrication. But I don't think we can just dismiss the guy's bad pinion bearings with "well, it's a pinion bearing, it spins faster than the carrier bearings" because that doesn't really tell us anything.
 
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Where are you coming up with this math? 375,000,000 rotations of the tires/axles/side bearings would indicate 2500 revolutions per mile at 150,000 miles. A 27" tire is 766 revs per mile.

I don't agree that the pinion spinning x times faster than anything else is a problem or contributing to any sort of failure. Sure, it spins faster than the carrier bearings and wheel bearings. That's all it spins faster than. The t-case input/output bearings and the transmission output bearing all spin the same amount. All of that stuff spins even faster with a regear but yet no one seems to be having problems with them (not including the pinion bearings in the discussion because they are usually replaced at regear time).

If one bearing spinning 3-5x vs another bearing is an issue, then we have to have a defined number of revolutions until bearing death before we can attribute that as the cause. Otherwise, with this logic, we could say exactly how long everything else will last, but we don't know that. The truth is we don't know any of that and we don't know that "being a pinion bearing" caused the guy's pinion bearing to fail. It's all being lubed constantly and experiences very little to no wear per revolution so I don't think we can really say "well it's a pinion bearing, that's why it failed." If we could, then we could also say all the stock Jeeps that shipped on 4.10s will expect to replace their bearing before all the Jeeps with 3.07s have to. Real world, we don't see that.

But back to the math. Call it 31" tires for an average tire size. Random tire on tirerack at 245/75R16 (stock Rubi) is spec'd to roll 683 revs per mile. 150,000 x 683 is 102,450,000 tire/wheel bearing/carrier bearing revolutions. Multiply that by 4.10 and you arrive at 420,045,000 revolutions for those 150,000 miles.

Let's look at an engine instead. Stock Rubi (6-speed) turns about 2350 rpm at 60 mph (used because 1 mile = 1 minute at 60). 2350 x 150,000 = 352,500,000 engine revs. Obviously we know of plenty engines going far far beyond 150,000 miles. Do revolutions really even matter past this point? Different style of bearing than a tapered diff bearing but still, moving parts nonetheless.

I don't think the guy angling his axle up killed his bearings, but I also don't think his pinion spinning faster than the carrier did either. I think the important part is that we can't predict longevity of any bearing really, many will last many miles despite their revs/speeds and some will be flawed and die due to their manufacturing or other factors like lack of lubrication. But I don't think we can just dismiss the guy's bad pinion bearings with "well, it's a pinion bearing, it spins faster than the carrier bearings" because that doesn't really tell us anything.

You know something? You are right! I messed up the math! I calculated the average pinion rotations per mile first by mistake and then re-multiplied that by 4.10. So all of my numbers are 4.1X too large. Still though, the pinion bearing is spinning many times faster and many times more per mile driven than the side gears. More speed and more revolutions does indeed affect lifespan. https://www.skf.com/us/products/rol...tion-based-on-rating-life/bearing-rating-life They use both speed and number of revolutions as criteria in calculating bearing load life.

I'm not saying that the pinion spinning faster, and more total revolutions, is the only possible factor in a bearing failing. But it certainly is a big factor. After seeing the oil circulation demonstrated in the video posted previously, and knowing that the pinion bearing does spin faster and more total revolutions that the other bearings in the differential, I think it is more logical to conclude that the life cycle of the bearing is a bigger contributing factor than the sufficiency of lubrication.