1:1 Repair Question

[RANOVRU]

So two days ago I put u-joints in the rear DS of my fullsize Jimmy. Done u-joints a million times before, nothing to it.

Yesterday I go into town & around 40mph theres a vibration that feels like its coming from the mid-back of truck. First thing I thought of was the tranny mount. You know how the saying goes, replace anything in the driveline & youre sure to find any other weak links. But the mount "looks" ok.

Ive been racking my brain since yesterday trying to figure out wtf could be causing this vibration. There doesnt seem like theres but so much it could be. I cant think of any reason why the DS would be causing this. I pulled it back out this morning to make sure there was plenty of free motion & nothing was binding.


Someone with a fresh perspective care to chime in????

[JeremyH]

Are the joints in synch? Maybe you need to have the DS balanced? Any apparent missing weights?

[JeremyH]

BTW, is this a slip joint or slip yoke style shaft??

[RANOVRU]

What do you mean by the jonts being in synch?

Theres one weight that was on the shaft before & its still there now. I wondered about having it balanced but never had to do that ever before???

Its a one peice shaft that slides into the tail of the tranny...

[JeremyH]

Ahh....ok.....so, it's a slip yoke style shaft. The ujoints on a slip joint style shaft can get out of synch (ears of shaft are 90* out of phase) if you dont assemble the shaft properly and can cause binding...however, I dont believe that this can happen on a slip yoke style shaft. Does this thing have a double cardan joint?? If so, did you rebuild that as well?

Yeah, I've had the DS balanced on my jeep before after dragging it across some rocks and it removed vibrations (mostly because mine was slightly bent).

Here, you can see the difference between the slip yoke style (top) and slip joint style (bottom)

[Tommy R]

Originally Posted by JeremyH

BTW, is this a slip joint or slip yoke style shaft??

Yeah, Jeremy is on the same line of what I'm thinking. Are your yokes in phase? Are the clamps all torqued well and fully seated?

[RANOVRU]

Double cardan joint??

The shaft is exactly like the one in the top of the pic you posted.

Note: There was no vibration before with the bad joints. The old ones didnt break so the shaft didnt hit anything/drag or get bent.

[KBrog]

That sure is an impressive drive shaft for a scaler.

[Tommy R]

Does the vibration go away at >40 mph or does it get worse? I assume no other changes other than the u-joint swap, right? Was it greased? Silly question, but it was the right size u-joint? You could always drop it, rotate it 180 degrees relative to the trans output or axle input, and see if that makes a difference. It shouldn't, but I've seen it happen.

[JeremyH]

Sorry....haha.....here is a DC joint:

These have a weird spring thing in the middle that can cause problems.

Anyway, since you dont have one, that cant be the issue.

I still say that either one of the new is bad, or the DS needs to be balanced. The shaft could have been out of balance all along and wore down the roller pins in the old u-joint to compensate. I would start by either having the DS balanced, or swapping in the old u-joints one at a time (pull the caps and inspect the pins and grease them first).

[RANOVRU]

Originally Posted by Tommy R

Yeah, Jeremy is on the same line of what I'm thinking. Are your yokes in phase? Are the clamps all torqued well and fully seated?

What do you mean by "in phase"? The straps that connect the ends to the rear all good &tight and the caps are flush against the yoke.

[JeremyH]

Originally Posted by RANOVRU

What do you mean by "in phase"? The straps that connect the ends to the rear all good &tight and the caps are flush against the yoke.

What he is referring to cant happen with a slip yoke style shaft. With a slip joint style shaft, it is possible to reassemble the shaft with the ears of the shaft (where the joint is pressed into) rotated 90* apart. This can only happen because the shaft can come apart in the middle. Not the case when you are dealing with a slip yoke shaft like yours...

[Tommy R]

Originally Posted by JeremyH

What he is referring to cant happen with a slip yoke style shaft. With a slip joint style shaft, it is possible to reassemble the shaft with the ears of the shaft (where the joint is pressed into) rotated 90* apart. This can only happen because the shaft can come apart in the middle. Not the case when you are dealing with a slip yoke shaft like yours...

Yeah, what Jeremy said. So ignore the phase comments.

[RANOVRU]

Originally Posted by JeremyH

Sorry....haha.....here is a DC joint:

These have a weird spring thing in the middle that can cause problems.

Anyway, since you dont have one, that cant be the issue.

I still say that either one of the new is bad, or the DS needs to be balanced. The shaft could have been out of balance all along and wore down the roller pins in the old u-joint to compensate. I would start by either having the DS balanced, or swapping in the old u-joints one at a time (pull the caps and inspect the pins and grease them first).

Yeah Im familiar with the spring in those joints. Done those before too.

What you said about wearing the needles down is making me wonder if the shaft is indeed out of balance. In one cap off the old rear joint the needles had turned to powder & the same end of the joint was very visibly worn. I just assumed it had done that because they were old & getting ready to come apart.

[Tommy R]

But wouldn't it have been noticed if the shaft were out of balance beforehand?

[RANOVRU]

I wouldve thought so too......IDK....

[Tommy R]

Silly question, but nothing else was touched? Wheels not torqued properly or something like that? Do you have another driveshaft to try temporarily?

[JeremyH]

Originally Posted by RANOVRU

What you said about wearing the needles down is making me wonder if the shaft is indeed out of balance. In one cap off the old rear joint the needles had turned to powder & the same end of the joint was very visibly worn. I just assumed it had done that because they were old & getting ready to come apart.

An out of balance DS could have been the cause for the failure of those roller bearings.....that and a complete lack of grease.

Originally Posted by Tommy R

Do you have another driveshaft to try temporarily?

Or, if it's 4WD, pull the shaft, put it in 4Hi and head down the road to see if the vibes are still there. I've done this before.....the torque steer is quite fun!

[RANOVRU]

Nothing else was touched. Checked lugnuts to make sure a wheel wasnt loose. Only happens when you give it gas at speed. If you let off the pedal it goes away.


Just got off the phone with a shop that balances DS's and explained my situation. Guy asked if the ears of the yoke on the rear ha the little insets for the caps to sit in. Im aware of what hes talking about but its kind of hard to tell. I have some of the clips that go on the outside of the caps on the yoke side. Think Im gonna try those and see if it helps.

[JeremyH]

Originally Posted by RANOVRU

Only happens when you give it gas at speed. If you let off the pedal it goes away.

Changed the control arm angle recently (or lifted the truck at all)? It sounds like the pinion angle might be too high and when you hit the gas, it rotates upward even further.

Originally Posted by RANOVRU

Just off the phone with a shop that balances DS's and explained my situation. Guy asked if the ears of the yoke on the rear ha the little insets for the ears to sit in. Im aware of what hes talking about but its kind of hard to tell. I have some of the clips that go on the outside of the caps on the yoke side. Think Im gonna try those and see if it helps.

Yeah, you definitely need the clips inserted into the recessed sections of the ears near the caps. The u-joint might not get centered on the ears properly without them....