The Stovebolt Site Forums The Shop Area General Truck Talk Vibration problem...

Need some advice here! On my '48 3/4 ton, when going down the road @ around 55, she starts to vibrate & goes away around 65. I pulled the drive shaft & had it checked & had a 4 wheel shop balance the tires (new tires) & check the rims for balance. The king pins are new, I've added an open drive shaft & T5 trans (that I had rebuilt). The vibration is not felt through the steering wheel. I have the shims under the springs & the leafs I rebuilt . Any ideas would be appreciated.

Maybe have a buddy drive down the freeway with you and watch or record your truck.

So that used to be a two piece draive shaft, correct? What kind of drive shaft do you have now?

I can think of a couple of things right of the top of my head to check first, lug nut torque and tire pressure. Without knowing what size/type tire you're running, I really can't give you much more of a suggestion on pressure than to start with the oe spec of 45 front/55 rear. Same goes for lug torque, manual calls for 90 ft/lbs.

Truckernix I think you might be onto something here....
I see labluver refers to the driveshaft in singular form.

Apparently drive shafts that are built too long can generate an oscillation and deflect as they spin.

labluver,is the vibration related to engine or wheel speed?

have the drive shaft balanced.check u-joints,put the truck on jack stands,go through the gears

Check the tires for balance again..............

We need more information, what type of drive shaft? how long is it? what gear are you driving in and what rpm does it happen?

Could it be engine vibration from low rpm in overdrive?

Joe

If you hadn't said the kingpins were new, that was going to be my guess. The '46 1 ton pickup my Dad had when I was a kid had bad kingpins. It would vibrate something fierce around 40 mph but then smooth right out again at about 45 or 50. We used to joke that that was when the guardian angel jumped out!!

A maximum measurement for a gas vehicle driveshaft or anything turning a high RPM is 54" weld to weld depending on diameter. That would be for a 3" x .090 tube. I've had to cut some down to that length or build a new one in larger diameter if it would fit in the vehicle. Absolute maximum is 60". However your vibration problem could be coming from some other source and sometimes can be really difficult to find. I'd also check the engine and transmission mounts as well as all angularity of the engine, trans and driveline. A common vibration issue is an out of phase rebuild on a driveshaft. If it is even a little bit visable then it it wrong. You've checked the obvious so start checking these suggestions.

You might try this to help isolate the problem. Get up to speed where it is vibrating then put it in neutral and let it idle. If it goes away then rev it back up to what you were doing and see if it comes back.

How about getting up to speed while on jack stands. That may tell you something too.

I had a vibration I thought was in my drive line. Before I could really do much about that my water pump went out. I changed it and no more vibration. But I would have sworn on a stack of Bibles that it was something with the drive line.

I have seen a service bulletin for WW2 Canadian Chevs that described vibrations being caused by having the u-bolts that held the u-joints to the drive flange overtightened causing binding.

This bulletin applied only to open drive shaft types with the u-joints attached by u-bolts (as opposed to straps).

The remedy was to ensure no binding of the u-bolts in the drive flange, torque the nuts to 23-25 ft-lb and stake the u-bolt threads below the nuts in case they started to loosen.