I think you've confused this scenario with another. If the U joint cross pins aren't lined up with one another (talking about from opposite ends of the driveshaft) you will get a vibration that's exactly like what you get with a bad u joint. We've got two International trucks at work that both suffered from this. The rear driveshaft on both were one tooth off on the slip joint splines putting the cross pins off. Both had a noticeable vibration at highway speeds.
I've had vibrations before and turning it 180 fixed it.. I thought it was a wifes tale as Frank suggested earlier, but it fixed the problem. I've never marked a driveshaft either when removing it, but I was told to flip it 180 after I said I had a vibration and it fixed it.
does anyone have this in a...repair manual... most likely the cups weren't seated in the yoke, when you flipped it you seated them.... ...my unmarked driveshaft is laying on the floor ready to be installed... when i get it back together and running, i will rotate it 180 and see if it makes a difference... ...Frank...
I haven't seen it in a repair manual, but I have seen it mentioned before to mark them IIRC. I'll look that up in a few minutes. I've never seen a yoke seat so easily to be honest with you either. When I flipped it all I did was unbolt the u-bolts, spin it w/ the transmission in park and bolt back up. I never removed it from the transmission, so it didn't get bumped around. It struck me as odd also why this fixed it, but it did.
Update: just looked in the Haynes for my Sonoma and Jimmy. Driveshaft Removal: *Raise the vehilce and support it securliy on jackstands. Place the transmission in neutral with the parking brake off. Block the Front Wheels to prevent the vehicle from rolling. * Using a scribe, a hammer and punch, or paint, make marks on the drivehsaft and the differertial flange in line wth each other. This is to make sure the driveshaft is reinstalled in the same position to preserve the balance. So, maybe it's not a wife tales?? Who knew. If anyone wants me to scan the page I can.
If anything, it's to preserve the wear patterns developed over time with the driveshaft and rear differential. Not the balance. Rear differentials aren't balanced that I know of. The brake drums are the only part of an assembled rearend that are. It would make no difference with a new setup, other than if you did have a vibe, it could help to flip it, that would be a 50/50 shot at a fix though.
I'm going by the book, and that is exactly what it says, so I posted it The ring/pinion has to be in somewhat of balance also, whether they balance them or not is another story.
Not saying the book is wrong, but the two assemblys as a whole aren't balanced as far as I've ever heard of at the factory.
While that is true, they still have to be somewhat balanced to start with. I'm not going to argue about it, just saying it has to be somewhat close to start with or just the gear oil wouldn't soak up all the vibrations. And there's a reason they put that in the Haynes manual, and the word "balance" instead of "wear pattern"
See figure 12 on this page http://www.autozone.com/az/cds/en_us/0900823d/80/14/ed/e9/0900823d8014ede9/repairInfoPages.htm Here is a site discussing balancing a driveshaft http://www.babcox.com/editorial/us/us50014.htm
