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Vibration between 1100-1500 RPM
I recently bought a 99 F350 Cab/chassis SRW 4x4 with flatbed dump. The truck runs great except for a vibration it came with that feels like a u-joint, but it's not. Below are the symptoms and what we've done.
Vibration between 11-1500 rpm. If you let off the throttle, or give it more, the vibration goes away. The vibration's usually felt in the steering wheel, but if you get it just right, it shakes the seat good too. It shakes the worst if the truck's under load, say going up a hill. At the end of my trip yesterday, I think the vibration occurs when the t/c and/or o/d are engaged. Since a VSS issue popped up over the weekend, I'm not sure at what speed's these happen, so not sure.
What we've done. Mechanic took the driveshaft out and checked the u-joints. They're fine. Greased those and the spline shaft too. Aside from scale, the shaft is fine and the balance weight is still in place. Took the inspection cover off the tranny and no signs of cracking on the flex plate. The t/c looked fine and the balance weight is on it, and didn't see signs of one missing. Drove the truck with the hubs locked...idea is a bad bearing in the front end. Truck still vibrates.
At this point, we're at a loss for what the issue is. He has a call in to a fleet mechanic friend who's worked on lots of these trucks. We'll see what he says.
Do you guys have any ideas as to what the issue is? Thanks for any help.