I have been noticing on the 09+ 1/2 ton thru 1 ton seem to all have this cylindrical harmonic balancer on the pinion end of the shaft. I was first noticing these on the new F250/F350 cab and chassis models on a dealership lot. I wonder if this really helps, and was this the answer to the dreaded vib problem on the 04-08 body styles., of which I never really heard what the root cause was. Just curious....rossford

 

Ford has been using those weights to move the harmonic imbalance inherent in a rear drive vehicle to another speed for decades on different vehicles. I first noticed them on a 79 Mustang and 81 Granada. Some vehicles are worse than others. If I remember correctly the harmonic shows up about 55mph. Adding the weight moved the harmonic up to a higher speed. I took it off the 81 Granada and it made no observable difference. the Granada still had a rear vibration about 55mph. I drove the Ford dealer in Raleigh absolutely mad trying to make them fix the vibration. The best thing they could do was spin balance the tires on the car. It helped but did not eliminate the issue.