Hi All, I have a 2002 SCab. 86,000 miles. 4.6l engine. 4R70W transmission. I have a rear vibration for several years. I finally am in a position to dig into it. The vibration is felt in the floor and seat of the truck at approx 36-44 mph and returns past 55mph. It is pretty annoying. I have replaced all tires with BFG Long Trail TA Tour. Wheels Road force balanced. Rear E-brake has been serviced and left loose until the vibration is found. Replaced the rear brake pads and rotors with Wagners Thermoquiets. I removed the driveshaft and took to a driveline shop for a balance. No change when reinstalled. I then reindexed, Again no change to vibration. Called the driveline shop and returned shaft to shop. When it returned it had two weights welded to each end of the shaft. Again no change. I called the shop, They said that they had trouble finding the balance. I feel that I have isolated the driveshaft as the problem. Also there are no leaks or free play at the transmission or at the pinion. The axle shafts are tight and no leaks. A rebuilt shaft from the driveline is approx $350.00, I can replace with one from a salvage yard for $80.00. My question is would the salvage yard driveshaft be inclined to the same vibration down the road? Will the driveline cost of $350.00 be the most cost effective solution?

Sorry so long,
John

 

Would be very surprised if a driveshaft suddenly goes out of balance without hitting something or losing weights. Have you replaced the u-joints, checked the rear diff? They can be the problem too.

 

Had the driveshaft checked by a friend mechanic. The driveshaft runout is 0.040 in.
I have found the problem.
Per Ford Repair Manual
Raise the vehicle on a hoist and remove the wheels. Rotate the driveshaft by turning the axle and measure the runout at the front, the center, and the rear of the driveshaft with the indicator. If the runout exceeds 0.89 mm (0.035 inch) at the front or center, a new driveshaft must be installed.

Anyone have success with salvage yard parts?

 

Wish you were here in KC... Guy on CL has one for $35 with a recent ujoint change. When I checked awhile back at junk yard they wanted 100 for one.