Puzzling driveline vibration

I just swapped a used NP231 with AA SYE in my jeep and when I drive with the rear shaft in, there is a bad vibration at only 15 to 20 mph. I haven't gone much faster because it's rough enough that I worry about something coming apart at higher speeds.

The history is that I swapped in a rear JK Rubicon axle that had a 1350 yoke on it. I installed a 1310 to 1350 conversion joint in my stock driveshaft with the slip yoke and drove it for about 2 weeks with just a slight vibration above 40-45 mph. I had pointed the pinion right at the current transfer case in preparation for the NP231 w/SYE, so a little vibration was to be expected since it should have been pointed lower.

I then swapped in a used NP231 that already had a SYE installed. When I took it out for its first drive, I couldn't even get it out of the neighborhood, the vibration was so bad. I thought the double cardan joint was bad on my used shaft since it wasn't as stiff as what I'm accustomed to, so I had a Tom Woods shaft that had only a couple thousand miles on it lengthened to work in the jeep. I put the newly retubed and balanced Tom Woods shaft in last night and the vibration is still there. I put the other shaft in again just for kicks, and the vibration feels the same between the two shafts.

I can drive on the front shaft only with no vibration at all.

I think I'm down to two possibilities:

1. Both shafts that I'm using are out of balance or in need of a rebuild.
2. The output bearing on the t-case is bad even though the yoke feels tight.

Am I missing any other possibilities?

did you carry over the conversion ujoint from one shaft to the other? is your pinion yoke loose? if someone regeared it and reused the pinion nut, it could have backed out a little.

if you have a gopro or even a digital camera that does movies, maybe you can film it and see what's going on under there. or put the rear up on driveshafts and have someone watch it while it's in drive.

I used a new conversion joint on the newly retubed shaft. The pinion feels tight and since the vibration was less noticable with the stock slip yoke shaft and stock transfer case, I'm guessing the pinion bearings are fine.

I'm thinking my next step is to put the rear axle on jackstands, like you suggested.

probably a stupid question and a longshot, but is one of your ujoints possibly sitting on top of one of the stop tabs on the yoke? the 2 tabs that keep the ujoint centered... that can easily happen working at night after a couple beers. ask me how i know :eyes:

Definitely not a stupid question. I did the same thing working in the dark last night. Fortunately, I could see it wasn't sitting in position, I just couldn't figure out why. In the light today, I found one of the needle bearings had fallen over and was keeping the cup from seating. Got it put back together and it still vibrates.

I took a video just now. I'll post it in a minute.

From the video, it almost appears that the shaft is bent, but both shafts I'm using have the same vibration (mph and intensity), so I doubt they are both bent the same.



This is the "spare" shaft, by the way. It's a couple inches too short.

First of all when you set your perches on a rear your yoke is suppose to be just below the TC ouput. secondly your ds could be needing a balance from the looks.

Pinion angle is fine. I just measured it. The spare driveshaft may be out of balance, but the newly retubed driveshaft was balanced yesterday. Both shafts create the same vibration meaning it comes on at the same speed and has the same intensity. Unless both shafts are out of balance the same amount, it must be something else.

thats not a balancing issue IMO, since it's highly visible at low speed. something isnt running true there. do you have access to a dial indicator with a mag base? runout should only be about .005", that looks like quite a bit. it would help to see both ends of the driveshaft spinning at idle, with a steady camera for at least 10 seconds or so per side. maybe a shot of the entire driveshaft at idle too.
if the runout is excessive on one end and very little on the other, then it's likely yoke or ujoint issue. if the majority of runout is at the weld closest to the slip joint, they welded it on crooked or the slip joint is bent.

Israel said:

Pinion angle is fine. I just measured it. The spare driveshaft may be out of balance, but the newly retubed driveshaft was balanced yesterday. Both shafts create the same vibration meaning it comes on at the same speed and has the same intensity. Unless both shafts are out of balance the same amount, it must be something else.

Click to expand...

makes me think there's an issue with the sye. maybe the output shaft is bent?

Vanimal said:

makes me think there's an issue with the sye. maybe the output shaft is bent?

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Good suggestion. That would explain why there is no play in the bearing and it would also explain the vibration.

The only thing is I would expect the vibration to be worse near the t-case than the pinion, but looking at the video, it seems to be about the same at both ends. It's probably still the best explanation at this point.

looking at the video, in the beginning the wobble seems to be greater heading away from the pinion yoke, which makes me think it's either a bent driveshaft or the problem is at the tcase end.
what about your centering ball? have you checked that?

The centering ball is a bit looser than I'd like. When the shaft isn't bolted in it normally takes a bit of effort to move the cardan joint around. It isn't loose enough to flop on its own, but it is easily moved by hand.

Vanimal said:

looking at the video, in the beginning the wobble seems to be greater heading away from the pinion yoke, which makes me think it's either a bent driveshaft or the problem is at the tcase end.

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X2.. That thing is def a wobbler. Have you watched the tcase yoke with no DS in? When you had it retubed, Who put the double card. back together?

Minor vibs with old tcase, to what looks like a bend DS with the case swap. My bet is the output shaft or yoke on the t case.

I did some measuring this evening and found that the crossmember I built puts the center of the t-case yoke an inch closer to the driver's side while the Rubicon axle has its yoke a half inch closer to the passenger side. My pinion angle is good up and down, maybe it's too far off side to side?

Seems like the u joint and DC joint should be able to make up fo the slight off set.

That's what I'm hoping.

I'll try and get a video tomorrow morning of the t-case yoke spinning on it's own and of the new driveshaft spinning at low RPMs.

it's best just to pick up a dial indicator, you can get them for relatively cheap. i think harbor freight sells one for like 19 bucks with a magnetic base. that way you can narrow down the runout and figure out where it's coming from. they're pretty handy for a lot of things.

This maybe another stupid question. In your picture you show the rear part of the DS. Did you take the slip yoke off of the DS? If so did you align your u-joints up when you put it back together? If they are not in align it can cause a vibration.

Vanimal said:

it's best just to pick up a dial indicator, you can get them for relatively cheap. i think harbor freight sells one for like 19 bucks with a magnetic base. that way you can narrow down the runout and figure out where it's coming from. they're pretty handy for a lot of things.

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I actually have one, I'm just not sure where to stick it on the Jeep to get a measurement.

O-TAY XJ said:

This maybe another stupid question. In your picture you show the rear part of the DS. Did you take the slip yoke off of the DS? If so did you align your u-joints up when you put it back together? If they are not in align it can cause a vibration.

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That's a very good question, actually. Even though I didn't remove the slip yoke, I checked it anyway to make sure it was installed correctly. It is.