Found my "bounce" tonight:

[Rob]

After gettting to the shop tonight I decided I really wanted to see what is causing the serious vibration, or bouce in the R612 truck/tractor. First I equalized all ten tires at 100psi and went for a short drive. Same thing, bounced like hell at 42-43mph indicated, and ceased at 48-48mph indicated. This is not a minor bounce but rather the type that will move you in the seat. I got the greaser out and greased everything that moves under that truck which changed nothing. I then jacked the front end up with the tires clearing the floor, grabbed a board standing it up next to the tire tread and spun the tires by hand. The steer tires were very close to perfectly round. This is where it gets interesting: I moved to the rear of the truck; with both drive axles supported on jack stands and the brakes released, using the same analogy with the board, I find the inner tire on the rt. front drive axle has an enormous flat spot about 3/8ths inch depressed. The lt. rear has the same inner tire flat spotted just about the same amount. With my board just off the tread and spinning the tires by hand, this really jumps out at you.

To prove what I expected I removed the four outer tires from the drive axles, and installed four rims, (Dayton) and went for a ride. This was like driving on footballs! I went back to the shop, removed the four inner tires, installed the original four outer tires on the inner, then spacer, then blank rims, and again went for a drive. The bounce was gone completely. The truck did ride like unladen camelback suspension does normally which is anything but smooth.

This truck sat for quite a spell before I got it home from the Texas heat. The tires are Kumho and in decent shape but the tires that are flat spotted are due to the outer tires next to them being flat, hence the flat spotted tires carried the truck weight for an unknown period of time. I don't know if running them at hiway speed with a load on them would round them out or not. I did reinstall all the tires as they originally were and will get a few more miles on them.

Rob

[Rob]

Hey, glad you found your problem!

It is sooo nice to work through a problem and something show up that points to a solution.

I hate mystery problems.

Bet you wish with all the tire changing, you had a pit crew to take care of it for you!

Yeah, but with old age comes wisdom, (as they say). I have dollies and jacks to do the lifting which was money well spent......

Thanks,

Rob

[Freightrain]

Hmmm, wish my bounce was as simple as that(as simple as that can get). I still need to get the arms out of the back and rebush them..........sometime???