Unusual driveline vibration case

[RickTheEngineer]

So I have this unusual situation. I was recently hit with some driveline vibration on my M1009, but it happened in a way that u haven't quite heard happen in the way mine did. At low speed (1-5ish mph) my truck as a noticable driveline vibration that shakes the cab enough for it to be heard and felt. I do have a 4" lift on it which might complicate things further, but please check out the details provided... I never had ANY vibration for the past 8,000 miles I have been using my truck post-lift install... It has a double caran driveshaft with the slip yoke. Here are some more details.

All new ujoints (8,000 miles ago)
New driveshaft (8,000 miles ago)
New output shaft seal (8,000 miles ago)
Ring and pinion look great (inspected 400 miles ago)
Tires balanced (no wheel weights missing)
Brakes are good (full service, drums and all 850 miles ago)

No strange differential noise (clicking, whirring, etc)
No grinding/binding sounds
No bent shafts
Ujoint bolts are tight
No rust around those spots

Could this be in fact a bad u joint? I did tow about 1,000 pounds for a 60 miles and it seems like it happened afterwards. Damaged ring/pinion? Only other symptom I can say really is that there is some tranny fluid around the body tub above the driveshaft joint closest to the front side of the truck (but what's even more strange is that whether I just drove or if the truck sits, there doesn't seem to be any sign of fluid leaking from the new output shaft seal I installed a few months ago, nor if the fluid right above it, it's above the joint, but the joint is dry?!). Anyways, sorry for the long post, I hope we can solve this mystery together.

 

[Chaski]

We need to get you a CUCV magic 8 ball.

What are your driveshaft angles like? What is your lift. Are you sure it is driveshaft ?

 

[The FLU farm]

"Tires balanced (no wheel weights missing)"??? That's like saying that the engine has oil...it did 8,000 miles ago and hasn't leaked a drop. But either way, the tires shouldn't be an issue at 1-5 mph.

Anyway, I would check the U-bolts for correct torque. And if you have lift blocks in the rear, and they are tapered "to restore driveline angles" as the ads often claim, that is suspicious to me.
Oh, and have those new U-joints been lubed in the past 8,000 miles?

And another "Oh". How are the motor mounts?

 

[RickTheEngineer]

welp, the driveshaft angle I do not have on hand, I will have to check that in the morning. I will definitely check those ubolts, although I would think that they should be good since I did actually check those about 1000 miles ago when I had nothing to do haha. As for the type of lift, it is a shackle flip in the rear, and the pinion visually speaking is at the same angle as its been thousands of miles ago, but I will take the time to check again. Also, The FLU farm, the motor mounts are actually on my to-do list on things to be replaced, do you think that could have tweaked something? And the Ujoints have not been lubed, it was something I was going to do tomorrow (I should have done it already, Ill admit that). Sorry for all the questions I have been asking on this forum, although I have gained so much knowledge from you helpful folk.

 

[porkysplace]

So how many months did it take to put those 8000 miles on ?

 

[joel]

Take it to s driveline place, have them check or balance the drive shaft, I did that to the mutts I have, no more vibration

 

[The FLU farm]

welp, the driveshaft angle I do not have on hand, I will have to check that in the morning. As for the type of lift, it is a shackle flip in the rear, and the pinion visually speaking is at the same angle as its been thousands of miles ago, but I will take the time to check again.

Technically, a correctly done leaf spring lift doesn't matter (to a point, of course). By moving the axle straight down, the front and rear U-joint angles change the same in both ends, and the resulting variation in driveshaft speed created by the U-joints gets canceled out. But with tapered blocks, shackle flips, etc. all kinds of weird things can happen. Yes, a double Cardan at the transfer case can help, but that kind of setup will only be correct at one given ride height. Hang a trailer on the back and it all changes for the worse - if it was set up right to start with.

But the speeds described are still too low for a driveshaft issue (that isn't painfully obvious) to be felt, I think.

 

[RickTheEngineer]

I accumulated 8000 miles over 7 months, as for the driveshaft, I think that would be good advice and Ill look into it, but all the weights from the original balancing are still there, not sure why it would change? I was thinking my process of diagnoses will be spinning the driveshaft by hand and feeling for vibration, then disconnecting the driveshaft from the axle and spin the pinion by hand and feel for vibrations... this should narrow some stuff down

 

[Jbulach]

My guess is that you cooked a u-joint, likely the one opposite the double cardan. Drive it, then check there temperature.


Sent from my iPhone using Tapatalk

 

[RickTheEngineer]

I personally am leaning towards cooking a ujoint as well, but do they really fail this early? Granted, I did a poor job of staying on top of the grease orders, but even still... plus also, it only has about 3 degrees on that joint so I would be surprised if that was the case, but I still suspect it is.

 

[Chaski]

A 4" shackle flip tilts your pinion up about 8 degrees.

Personally if I had a M1009 with a 4" shackle flip I would put a CV at the transfer case end of the driveshaft and shim the axle so the pinion aims at the transfer case.

 

[The FLU farm]

but all the weights from the original balancing are still there, not sure why it would change?

Because, as I tried explaining earlier, tire balance doesn't last forever. Tires wear, and there are other factors within the tire that affects balance over time.
But it's a moot point in this case. For tire balance discrepancies to be felt at 1-5 mph you'd have to have nearly square tires.

 

[The FLU farm]

I personally am leaning towards cooking a ujoint as well, but do they really fail this early? Granted, I did a poor job of staying on top of the grease orders, but even still... plus also, it only has about 3 degrees on that joint so I would be surprised if that was the case, but I still suspect it is.

I have run many thousands of miles with over 25 degrees on the U-joints (good for about 300 rpm according to Spicer) that routinely see over 3,000 rpm.
But I also grease them regularly.

 

[RickTheEngineer]

in regards to the vibration, it happens rapidly enough where there are seemingly like 6 oscillations per tire rotation so it probably isnt the tires. I have spicers in mine as well, and I know none of them really exceed more than 15 degrees. as for the pinion angle, it does point to the tcase, just a midge below to account of axle wrap, which is what I was told to do by the driveshaft shop that I took it to months ago. none the less, the angle and other parameters have not changed. I became aware of this problem after towing a trailer, I wonder if that agitated anything.

I also wonder if I need to replace the tailshaft bushing since I have signs of a leak.

 

[Chaski]

Do you have a CV at the transfer case?

 

[RickTheEngineer]

By CV do you mean a double joint? If so, then yes I do, no slip yoke eliminator... kept the slip yoke and added a joint

 

[rustystud]

Check your transfer-case for cracks. You could have cracked the housing and this will cause your problem. Also check the output yoke of the transfer-case. Try and move it up and down. If it is moving more then a few thousands then the bushing is bad.

 

[cucvrus]

My guess would be to make sure the C clips are on the rear most U joint caps. They keep the U joint centered in the yoke. They would be the C clips on the U joint caps at the rear. Good Luck.

 

[cobia2017]

I have had a very very similar vibration and sound as per your description...with replaced door bushings and pin/striker adjustment and tightening down on something on gas tank, the vibration was largely reduced to a very tolerable level, also the gas tank door required slight adjustment as it was vibrating... however, it is still present (the core source is still present but with all the secondary rattling it caused-the sound is much better)...will check u joints next...my motor mounts were replaced but did not change anything...good luck, I will anxiously await your source as it may be mine!

 

[Barrman]

Besides the suggestion of temperature checking your u-joints a few post up. Pulling the straps off the pinion yoke and actually holding the drive shaft/u-joint as you check them and turn them can do a lot more than just looking and giving them a tug. This will also make checking the transfer case bushing easier too.

Something not mentioned above is the transfer case to cross member mount. Motor mounts have been mentioned but if the rear mount is broken, things are just flopping around back there. True, this is normally felt at higher speeds but you will be right there checking the u-joints anyway. See if you can bench press the transfer case up or not.