Driveline Vibration - Bent Driveshaft!
 

So my truck started vibrating around 60mph idk maybe a month or two ago. I only noticed it in the 60s and really only when I would let off the gas.

Fast forward to now, and the issue has become substantially worse. I've especially noticed it getting worse in the past two weeks. Basically any speed over 55mph I notice vibration, whether or not I'm applying the gas. The vibration on the freeway is accompanied by a subwoofer-type hum and is jarring enough that it concerns me quite frankly. It feels like the whole truck is going to fly apart. I also notice squeaking coming from underneath at lower speeds, rpm-related.

I did some research online and came to the conclusion that this was a u-joint issue, but to confirm I brought it in to some local car guys I trust and they went under the truck to give the driveshaft a tug and informed me that there is no play in the driveshaft... and in fact the issue is that the driveshaft is bent towards the driver's side!

Bear with me here... I do not know EXACTLY what they were referring to that was bent toward the driver's side. He said there's a u-joint at the back and at the front of the driveshaft and that the back one is fine. It's the FRONT of the driveshaft that's the issue. And he said it was the u-joint that was bent towards the driver side, and/or the driveshaft. Something like that. I went under the truck myself afterwards to try and see what they saw and I couldn't tell. All I know is that they could tell immediately, so I guess it's pretty clear.

I asked how that could be possible and they said torque. Or potentially towing, which I don't do. But I do have a manual transmission and my driving style 100% of the time is foot to the floor 2000rpm to get maximum torque out of the engine, then generally shift around 3000 to 3500rpm. Can anyone give me some ideas on what exactly is up/the issue is and what I need to do to fix it? Is it safe for me to drive on the interstate? I can't get it into a shop until a week from now. Anyone heard of this kind of thing before? Thanks so much.

Assuming you have a 4wd you can confirm it’s the rear driveshaft by putting the transfer case in 4wd high and removing the rear driveshaft. You will essentially be driving around in front wheel drive and it will not cause any damage to any drivetrain components. If you remove the rear driveshaft and the vibration goes away then you have found your culprit

Sounds like the Cardan joint might be the issue.

have you checked your tires? i had the same exact issue back in december and got some new tires and the problem basically fixed itself. saved me a lot of money and headaches.

Why not just put the front end on jack stands, get under, and look for yourself?
Maybe you will see what the shop is talking about.

And giving the shaft a "tug" to check for bad u-joints isn't always a reliable method. I've seen ones that seemed good until I unbolted the shaft and then found one bad.

Plus, while it's off the truck, set it on a nice flat surface and roll it side to side. If it is bent it will show up.

The only way I could see it being "bent" at the front u-joints is if perhaps the center ball in the cardan has froze and is kinked to one side, unable to move freely or easily. But if that was the case you would almost certainly have a horrible squeal with it. Idk, what you've described sounds exactly like a driveline vibration but the reason the shop gives sounds funky. I agree with above and suggest pulling off the driveline and checking for yourself; takes maybe 5 minutes to do and problems become real apparent when moving the joints around by hand. Another good idea would be to get the rear tires off the ground, put the truck in gear and start poking around while it spins.
I'm curious if they just got a funny look at it; I've noticed sometimes when I'm under my vehicle the driveline looks crooked and off to one side, even though it's straight as can be.

Finally took it in. They told me the front U-joint was coming apart and fixed it, but told me the vibrations are from the steering rack bushings which I guess have been coated in oil from a leak. The u-joint replacement did not fix it. Does that sound like a common cause to you all?

Does your steering wheel vibrate/shake? If yes, then I would suspect steering rack bushings/inner tie rods/outer tie rods/front tires out of balance. If no, then not likely to be your steering rack bushings.

Take it to a driveline shop and have them look it over. It took me two years and three driveshafts to get mine right after the center ball on my factory driveshaft wore out.

These things are apparently really sensitive to driveshaft balance so “eh good enough” ...isn’t.

I threw many parts at a similar problem until I bought a new OEM driveshaft, that fixed the issue but not after spending a lot of unnecessary cash.


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It now appears, according to the shop, that the vibration is being caused by my front differential mount bushings, which are oil-soaked and falling apart. Does anyone have experience with vibrations on the freeway coming from this specifically?

I do not, but it is very possible if the mounts are degraded. The front axle shafts are constantly spinning regardless of 2wd/4wd so they could easily be causing the front diff to move around and vibrate.

Here are two images they provided me with:

https://filestorage.autovitals.com/F...518af60336.jpg

https://filestorage.autovitals.com/F...04d3c13ae3.jpg

Bushings not in best of shape but I see enough good I don't believe they your problem.

I would stop going to this place unless you know the people there. This is the third thing they said was wrong with the vehicle, and they still haven't fixed your problem. I'm sure they'll figure it out eventually but at what cost?