New vibration after replacing u-joints

[cropduster]

Hello, everyone.
I have just replaced both rear driveshaft u-joints on a 2005 4x4 Explorer V6 (it had some of the symptoms, like clunking when engaging Reverse). I installed the heavy duty non-greasable Spicer ones recommended by RockAuto, and I used a ball joint press.
After re-installing the driveshaft (I marked flanges, yokes and the shaft, so I'm sure it went in exactly as it came out), my Explorer developed a new vibration that starts around 35MPH and is /very/ strong around 50MPH.

I removed the driveshaft again, hit yokes and driveshaft with a rubber mallet (just in case one of the u-joints was binding), re-assembled, same vibration.

I took her to a local mechanic, who told me the driveshaft is shot, won't be able to be balanced and needs replacing. I took her to a different mechanic and he told me that the driveshaft is not bent, but the slip joint in the middle of the shaft is loose and flexing too much (which I didn't even know was possible). The 2nd mechanic recommended me to go to a driveline specialist to double check.

How does this sound? Is the slip joint (which is behind a rubber boot) serviceable? What else could have happened? Both mechanics told me the u-joints are good and the installation was good (so at least my pride is not hurt).
Thanks!

 

[Fix4Dirt]

i wouldnt think the whole DS is shot imo. slip joint is usually serviceable

 

[cropduster]

I'm gonna be taking the whole driveshaft to a driveline shop for a third opinion. I'll update this thread when I have an answer.

 

[410Fortune]

Your driveshaft only has two u joints and a slip yoke??

Normally a rear d shaft with only two u joints has a slip yoke at the transmission/transfer case
I’m perplexed because the second mechanic said the slip yoke in the middle of the shaft is shot

I would like to see this rear drivesahft
What I see online is a solid rear shaft with a slip yoke at the back of the t case which makes sense. The second mechanic was full of it? Something does not add up

Any looseness in the rear pinion?
Any work done to the front d shaft?

You could remove the rear shaft turn it 180 and re install

 

[cropduster]

Your driveshaft only has two u joints and a slip yoke??

Not like that. It's a 3rd gen 4x4. On those, the rear driveshaft looks like a single piece with a u-joint + yoke combo on each end. In reality, there's a slip joint in the middle of that single piece, behind a rubber boot. There's no slip yoke on the 3rd gen 4x4s. If I remember correctly, the RWD ones have a slip yoke that attaches to the transmission.

 

[410Fortune]

Is this what your d shaft looks
Like?

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The slip yoke should be simply
Lubed I have never seen one If these “wear out”

It sounds like you are not real sure your u joint install went correctly? But that’s just what it sounds like. If the joints are seated and snap rings in place then chances are you did it correctly

It is quite possible that you had a drivetrain/driveline vibration before and by fixing any Loosness in the rear shaft you have amplified the vibration at its real source

You may try unbolting the d shaft and rotate it check your alignment and fitment

Could also raise the rear axle put truck in n and try spinning it look for any looseness in the pinions

 

[cropduster]

Yep, my driveshaft is exactly like that one.
Regarding the u-joint installation: I've triple-checked everything and I think I did it right, but even though I'm comfortable doing most of the maintenance on my Explorer, this was the very first time I've done u-joints. It's perfectly possible I have screwed up somewhere.

I'm kind of trusting the two mechanics that looked at it, told the u-joints are good, and pretty much pointed in the same direction as you did: new u-joints are amplifying the real source of the vibration.

I'll post back after I take the shaft to the driveline shop for investigation.