Running fine..then..sudden vibration

[Dubv1980]

So I was driving my '73 Series III to work this morning, and I suddenly get a very noticeable vibration. I pulled over, looked under the truck..nothing. Start the truck back up again..vibration still there. Seems to be related to the engine, not transmission/suspension etc. Any ideas...it was very sudden. One minute, running fine, then bang, heavy vibration. I was able to drive the truck a half mile or so back home, but I haven't had a chance to investigate further. Any ideas?

Chris

[KSMTAW]

Could be a bad Universal joint.

put the truck in gear and set the e-brake. Grab the drive shaft and try to rotate or move and check for wear. There should be no movement in the u-joint.

V/R
Todd

[Les Parker]

Is the vibration there when the vehicle is idling?
Does it make a difference when the clutch is depressed?
It maybe that the centre of the clutch has reached its "sell by date".
Some further info would be required to further diagnose.

[jp-]

Could also be a blown motor mount.

[Terrys]

I'm with Les, thinking you may have a pressure plate problem. Maybe pilot bearing so worn as to allow input shaft to have wandered off center. Is the vibration there with the clutch depressed?

[LH Drive]

If the pilot sleeve is worn out, would'nt this cause a bind on the front tranny counter bearing. The gears would not mesh right making noise as the gear teeth grind and break off.
What about checking the tranny rubber mounts. You could jack up the tranny to see if its still held in place. Same way to check/replace the engine mounts, just use a wooden block so you don't damage your jack .
I also had a u-joint snap while driving, truck always seamed to vibrate since I started driving it. I thought it was my Mud Rover tires. After I replace both u-joints she runs smooth even with the new tires. Friend of mine told me to cross mark the u-joint caps with a metal marker. They will start to spin just before they go out. The cross marks will show this if you keep an eye on it.

[Dubv1980]

After further review

The vibration is there...clutch in or out, and also at idle. After looking under the truck last night, I noticed that the bottom portion of the fan shroud had cracked off, and the break looked fresh. It was dark so I couldn't get a good look at the motor mounts...but would that point to one of the engine mounts failing? The engine seems to be running fine..just making the truck vibrate now. I'll investigate further tonight. Thanks for all the ideas.

Chris

[jp-]

Did the fan lose a blade?

[Dubv1980]

Yup

The fan did lose a blade. Would that cause some virbation? I can't see any problem with any of the motor mounts.

Chris

[jp-]

Would that cause some virbation?.

Chris

Yes. Quite a lot actually.

Replace the fan.