The Stovebolt Site Forums The Shop Area Engine Shop vibration in 4th gear

my 56 3/4 ton has a vibration when in 4th gear. my dad says he thinks the drive shaft has been turned or not replaced when removed to the correct in line status. he says the shafe has marker points to put it back in exactly as removed. I cant find marks like this on my truck. I did remove the 2 piece drive train during restoration.
any hints or pointers on removal of the shimmy or vibration? I have new balanced tires for what its worth.

It's possible the yokes on your 2-piece driveline are not oriented, or "clocked" the right way. HERE'S the procedure from the shop manual (paragraph 1(a) under "Installation").

Hope that helps.

Waldo, when the instructions state "aligned", aligned to what? are there markers or arrows? all install info in the manual was followed when I installed it. what I think my issue is I removed the rear 4 universal joint flange u bolts and took out that section of the shaft. I didnt know to mark the shaft to make sure it went in exactly as removed. I guess I need to know how to put it back aligned???

Well, the instructions aren't easy to follow but here's what I think it means;
The yoke that is permanently attached to the front driveshaft - and the yoke that is attached to the slip-joint on the second shaft, have to be in sync (facing exactly the same direction - aligned to each other). In other words if the front yoke is oriented to, lets say, 9 o'clock, and 3 o'clock, the slip joint yoke has to be exactly the same. That's the way I read the instructions but I don't have a 2-piece driveline. Hopefully someone with some experience with this will chime in.

Well I don't know about the alignment either. I did notice in my sons nissan manual that they recomend rotating the propeller shaft 180 degrees if it vibrates and is out of balance. If that does not fix it they say to replace it. Personally I think I would try rotating it 180, test then 90 more test then 180 more test then give up or use the position that vibrated least. So basically test in all 4 positions.

On my 57 I had a shop replace my transmition once and I watched them drop the bearings out of the rear U joint. Seems like they were needle bearings. They picked them back up and re assembled them into the bearing and it is still working 15 years later. But then it has only gone about 5 thousand miles in that time.

Sounds like it only vibrates in 4th so at high revs where you might expect it. I would vote for doing a 180 degree rotation o it since you do not know where it was when you took it off. You might want to mark where you have it now so you can tell where you are moving it to for testing.

But like I said I do not know much about the alignment thing for the driveshaft.

I like the turn 180 idea. I am certain when I took this apart at the u bolts by the rear end, theres no way I would have placed it exactly back the way it came off. I jsut didnt know it mattered. I have no bends or damage, the universal joints and needlebearings all look good too.
it would be great if there were arrows to line up for each piece wouldnt it??

I could be wrong but wouldn't turning it 180 degrees put you at the same clocking as before. If your slip yoke has 16 splines in it, you have 8 possibilities. Sounds to me like the shop man. is saying the intermediate yoke on the spline has to be in alignment with the front yoke. Is it?

i think where it is is not clocked correctly and 180 would make it jsut as far out the other direction. BUT, how do you align the intermediate splines and front yoke? I do not know how to tell if it is aligned.

56;
Maybe the word "aligned" is a little misleading. I think "phased" or "synched" might be better.

The manual suggests doing this "phasing" while the entire driveling is sitting on the floor. I think it is saying that you lay the front driveline out on the floor and note the position of the yoke that is welded on to the tube, then you insert the slip yoke so that it is in the same clock position as that front yoke is (even though it's facing the opposite direction the yokes are exactly in phase) then you reinstall the driveline.

Maybe you should start a new post and ask about 2-piece driveline synchronization, or phasing.

Good luck, I think you're on the right track.