started the other night, pretty bad at speed, not related to engine speed just when the truck is going around 50mph. checked out the wheel bearing and all are good, got under the truck to check the drive shaft and other stuff and I was able to wiggle the drive shaft at the transmission. My truck has a 3spd manual car style trans with the long tailshaft and i was able to move the shaft just a little from side to side.

it was the yoke moving in the tailshaft not the u-joint. What kind of problem am I looking at here. Time for a new trans? I do have a original 59 truck trans in the garage but if I swap to that I have to get a new drive shaft.

 

Does your truck have a one or two piece driveshaft?

If it's a two piece driveshaft, there's a drive shaft center support (aka carrier bearing) located between the two shafts that has a roller bearing inside it. If the bearing goes bad, the vibration will radiate throughout the truck.

There's always a little play in the driveshaft...that's normal. But..if the u-joints are bad, there's another cause of a vibration.

 

forgot that part. standard one piece shaft

 

A bent wheel, out of round tire, or a broken rear spring could also be the source of the vibration. Cracked rubber motor mounts is another cause. The rear mounts especially are well known to crack & sag from age. I seriously doubt that the internal parts of the transmission are causing a vibration.

 

well I did have a bad tire but that was replaced and no change. all the springs check out and the motor mounts looked ok. I will check them better tomorrow need to clean some gunk off them to really see them good.

But after checking today the tailshaft was the only thing I found that seemed out of the ordinary, thanks for the help as always.

 

There is a bushing in the tailshaft, but it isn't likely the cause of this. The driveshaft could be out of balance or slightly bent. Is this a setup (trans/driveshaft/rear end) that didn't vibrate before, or is it a new combination?

U-joints can feel tight (no play) but have dents in the cups from needles that aren't rolling.

 

this is my daily driver, been running this drive train since april with no problems.

 

You may try putting the rear on jack stands and turning the rear tires with it in neutral to see if the drive shaft is bent or a universal is bad. Just be careful if you get under it.

 

Could have thrown your Wheel Ballancing weights.

 

all very good points I did not think of..... I'll let you guys know what I find.