Low level vibration. Failing alternator or front diff?

[Paul_Driver]

Recently I have become aware of some low level vibration when I'm cruising at about 65mph. If I stay below this speed it is imperceptible.

I've had a whining front diff for some time now and was told that this would eventually result in vibration before the diff packs in altogether. So when I noticed it for the vibration for first time recently I wasn't too surprised.

What has surprised me though is that when I increase my speed to 70mph, the vibration becomes quite noticeable and my dashboard lights starts to flicker. I don't know how the diff would effect the electrics, so I'm now wondering if the vibration is indicative of a failing alternator rather than the diff.

What do the panel think?

 

[Jon Wildsmith]

Can't see the alternator causing vibration Paul, noise yes but not a vibration you can feel at 65-70mph and it would be engine not road speed dependent. Has the diff noise got any worse? Might not be the diff, could be prop shaft UJ's, doesn't have to be an existing fault might be a new one

 

[Paul_Driver]

Hi Jon, I'd say that the diff noise has gotten gradually louder over the last year or so. It's noticeable when I've got my foot on the gas but not when I'm coasting or decelerating. Very puzzled by the electrics.

 

[Jon Wildsmith]

The electrics sound like a marginal connection somewhere, possibly on the alternator, that gets excited by your vibration. See if you can feel any up / down / left / right play (not rotational play) in the front diff pinion as that will often cause a vibration and noise. After that I'd be checking the prop shaft UJ's for play and free movement with them off the truck.