The Stovebolt Site Forums The Shop Area Engine Shop 1934 truck occaisonal vibration in 4th gear

I have a 1934 chevy 1 1/2 ton long wheelbase. I am trying to find what causes a vibration when I'm in 4th gear and going over 30 miles an hour. It doesn't occur all the time. If I let off the gas and step on it sometimes it will go away. I have the propeller shaft off and the tranny open though the PTO opening. Inside the trans look fine an feels tight. The ujoints don't seem to have any play. I did find wear on the front propeller shaft and bushing. It looks to be a little less that 1/16th of an inch of wear. Would this let the ujoint behind the trans slide off center enough to create this vibration? Does anyone know of any other possible sources of a vibration like this?

There is another bushing in the main long torque tube behind the intermediate shaft. There shouldn't be more than 0.005" run-out at this bushing. Did you check the trans. third and High speed (4th)sliding gear for wear or excessive play on the main shaft.

You might just need new engine mounts.

The 34 truck has solid metal to metal engine support mounts at the clutch housing the only rubber mount is the front one. The rear mount is also a metal to metal mount at the intermediate drive shaft support bearing to the cross-member.

I have a new front engine mount. Rear is steel. I haven't looked at the shaft behind the middle ujoint yet. The vibration feels like it is closer to the tranny, but it's hard to say for sure. With the PTO cover off I had my son shift through the gears. I didn't see any excessive wear of feel any looseness in the gears when I rocked them by hand.