Vibration

[Spinner01]

Hello All!

I have a 68 F250 Camper Special LWB that I purchased from the original owner about two months ago. It had some charging issues, needed new tires and shocks and a new water pump. After replacing the shocks, tubed bias-ply tires and steel split rims with radials and aluminum rims, and fixing the other minor items, I have begun to notice a minor vibration once I reach 40 mph. The vibration disappears at 45 mph. The vibration felt similar to a U-joint vibration, so I replaced all 3 U-joints. Unfortunately, the vibration is still there. Again, it's a fairly minor vibration but still perceptible. There is no accompanying noise that I have noticed. I've considered going back to the tire shop to see if I may have lost a wheel weight but I would think an unbalanced wheel would produce a vibration that would increase with speed, not only be noticeable between 40-45 mph.

Any ideas? Thanks in advance for any help.

[Spinner01]

Forgot to mention that the transmission is a C6. The truck has 107,000 original miles. The truck came with a 360 but the original owner had it rebuilt as a 390 at about 100,000 miles.

[Ranchero50]

Put the truck on jack stands and run it up to speed while watching the drive line. Typically you'll see what shaking. Just be careful that it doesn't come off the stands.

[Bronco_77]

I had a 82 4x4 Toyota truck one time that the guy I bought it from just used on a farm and he had put a set of tires on it and not even balanced them at all. It drove fine till u hit between 40-45 then it would vibrate perty bad but was smooth as soon as u hit above 45 on.

[Spinner01]

I like the jack stands idea. I'll give that a shot. Appreciate the replies.

[dpson]

Your truck should have a two piece drive shaft with a slip coupling just behind (rearward) of the driveshaft support bearing. If the front driveshaft became separated from the rear driveshaft at this coupling it may have been put back together such that the two shafts are "out of phase" and this can cause vibration. I believe the service manual has a section on how to check and correct this.

[Ren]

You didn't mention replacing the carrier bearing. It's a pain if you're not a pro at it. I managed. But I have time, patience, and tools.
The driveshaft being 'out of phase' is a real possibility. You can find pics online of how to properly phase a two piece driveline.
Before you condemn the wheels or driveshaft as the source of your problem, consider that it may be the harmonic balancer.

Run the engine through the rpms while the truck is parked. If there's undue vibration, you know it isn't the wheels or driveline.

[cep62]

The driveshaft being 'out of phase' is a real possibility.

I've seen that more than once, on what looked to be factory installed driveshafts.

consider that it may be the harmonic balancer.

I put a used flywheel on a 400 that was out of balance , pulled it out and had it resurfaced (again )and it was better but still vibrated .
pulled once more and put on a new one and it was smooth. I could see nothing wrong with the bad one, it was just out of balance.