Drive shaft bent

[KY_GMC]

I know this topic has been discussed in the past, but I am offering up my recent experience.

I completed my build last year [72 GMC C1500 w/ leafs] and have been driving the truck sporadically and put around 1400 miles on it since the build. This fall, I found a straight frame and did a complete frame swap, re-using the front and rear suspension [long story!].

After the frame swap, I started noticing a oscillating vibration around 55 - 60 mph. One of those on/off vibrations. The drive shaft was originally rebuilt and balanced at a drive-line shop and I had no issues before.

I took the shaft back to the shop and they said that the shaft was bent. The middle section was moving around at speed. They took all the weights off, straightened the shaft and then re balanced it. Still need to install it to see if it fixed the issue.

Has anyone ever had a bent shaft from just spirited driving?

I haven't hauled anything nor pulled anything with the truck so far.

Just trying to figure out what would cause the shaft to bend.

[brad_man_72]

Hitting something or replacing parts is about the only thing I've seen that will bend a driveshaft.

Excesssive rpm can cause a bend in the tube at the middle of the tube... bad things happen very quickly after that.

Hitting something or the shaft coming out of a moving vehicle like a broken rear ujoint can cause a bent shaft.

I've seen shafts break from torque and traction but not bend.