Unloaded vibration

[Billw69]

Anyone experience a driveline vibration while in an unloaded condition? Curious about what might cause a vib above 70 mph, and is amplified when pushing in the clutch, for example during a shift. This vibration increases in frequency above 70mph.
The car has a new clutch, rebuilt transmission and axle, replaced driveshaft and yoke as well as u joints.
Thanks

 

[basstrix]

I've had a failing pinion bearing or loose pinion nut cause noise and vibration unloaded but quiet down when loaded.

 

[Billw69]

Thanks, no options are off the table yet. Input bushing to bent axle…… although I’d think a bent axle wouldn’t change frequency when I push in the clutch. I find myself wondering if it could be related to the driveshaft or the hardware on either end. I’m going to clock the driveshaft 180 degrees in the axle yoke and double check the u bolt torques as my next move, (least invasive).

 

[basstrix]

Another case I thought of was one of the alignment tabs on the pinion yoke was worn down...probably from running with a loose u-bolt. The cap of the u-joint was able to move outward and let the u-joint move back and forth along the trunnion axis. I know the vibration changed with and without load, but I can't recall how it changed. I welded up the tab and re-ground it and the vibration went away.

 

[Billw69]

Good input, thanks. I did notice that the tabs in the pinion yoke made for a VERY snug fit, as in I have to use a pry bar of appropriate nature to unseat them.

 

[Tnfastbk]

Driveshaft angle or possibly out of balance??

 

[boilermaster]

Billw69,
My number one question would be, when did this all start ?
Did you inherit this issue from a previous owner or did this happen during your ownership ?.
the easiest answer would be a u-joint cap needle bearing folded over on one of the caps making the fit to the pinion yoke too tight.
have you tried fitting a new uninstalled u-joint to the pinion yoke ?
With more detailed information we can be better detectives.
For instance : what engine and transmission ?, was engine align bored, how did bell housing fit and how hard or easy did the transmission install.
what about engine dowels and runout ?
this is going to be a who, what, when where and why investigation.

 

[rvrtrash]

I've seen the driveline yokes/ears bend in if the u-joints aren't pressed in or out correctly, which binds up the u-joints and changes the center slightly.

 

[Billw69]

Thanks guys, for taking the time to make input. I inherited this issue and while I’ve tracked it down to where it appears to come from transmission back. Curiously as I’m driving the car at 75 or 80 and I push the clutch in the vibration actually gets worse. Rev the motor no change.
That’s got me thinking. It’s transmission and back issue.
brand new clutch rebuilt transmission brand new driveshaft rebuilt rear end new axle housing new Springs and new U joints.
As I mentioned earlier, when I replaced the U joint in the rear axle pinion it fit very snuggly, as in I need a prybar to get it out or when I reinstall them, I can only get them into position if I tighten them with the U bolts. That strikes me as being a little too firm. When I had the rear u joint out, I removed the two caps and the needle bearings appeared to be in good shape. However, there was one that was suspect, although it was the only needle bearing that I saw that looked different than any of the others in that cup. In its current position, I’ve clocked it back 180° added grease to the caps and re-torque the bolts to 17 foot pounds their dimension is 1 and 1/8 diameter. I think that may be a 330 u joint? I hope to test drive it today and just to eliminate another possibility, I was gonna change the rear U joint to a Spicer for added strength.
I’ll update the progress after my test drive. Thanks again to all for chiming in.

 

[Tnfastbk]

any local driveline shop should be able to check your driveshaft for balance.

 

[Billw69]

When I put a dial indicator on the shaft it’s measuring .020 rear, ..015 middle and .023 front. I forgot to mark the high spots on the shaft to identify its shape.

 

[Tnfastbk]

I took mine to a drive line shop and the spun it up on their machine. It was super cheap and I could definitely cross it off after that. Mine ended up being a little pinion angle and a worn yoke. I found out Ford makes a long and short yoke as well.