Before you take it into Ford, note the speed where you first feel it and accelerate until it goes away (if it ever stops). Next, see if you get the vibration when the engine and driveline aren't under load, either coasting or going downhill. Then downshift and make sure the vibration is not engine speed dependent. Next, while you tool down a straight smooth road, have someone walk through the cruiser and listen for the noise from the vibration. These tests help determine if it's a transmission, engine, or driveline problem. If the vibration is always present, you probably have a driveline problem.
I think PC outsources the extension work. Whoever does it adds a 4' section of driveline (on the 2552) to the driveline. This add on is what caused the problem in my PC. However, the problem was not the new 4' tube, but the whole driveline. As delivered, the Ford 2 piece driveline is probably just fine, but when you start messing with it by changing the angles and lengthening it, any out of balance situation can go from unnoticeable to terrible. Ford is very likely not at fault and the outfit doing the extension really isn't at fault since they probably never drive the extended unit and their 4' section comes balanced, but when everything is combined along with several thousand pounds of payload, it doesn't work right. At least not on my vehicle.
Unfortunately, if the original owner doesn't complain during the warranty period, you are out of luck. The good news is once you have identified the problem, it's not too expensive to fix and the fix can be done in a couple of hours if you have the right equipment.
There are 2 fixes: The best fix is to replace the 3 piece driveline with a 2 piece driveline. This requires a larger diameter driveline shaft and rebalancing the entire driveline. This is the most expensive fix because you have to buy a long, large diameter, piece of heavy duty driveline. It is the best solution because you end up with a straighter shot from the transmission to the rear end, a stronger driveline (beefier part), less parts (one less u joint), and it will provide smoother power due to less flexing (a 4" driveline that long allows for a lot of 'jumping' due to twisting under acceleration). My thought is PC doesn't do this as standard procedure because it adds cost to the unit and it generally isn't necessary.
The second fix is to pull your entire shaft and put the whole driveline on a balancer using the same angles as found under your PC. My guy initially put shaft 1 and 2 on the balancer and balanced that part. Then he put shaft 2 and 3 on and balanced that part. He did this because he didn't have the spacers required to put the entire 3 part shaft on his balancer. It's long and most shops don't deal with drivelines this long. He put the driveline back on the vehicle and drove it and it was far worse than when he started! He called the company that makes the balancer and they told him he would have to put the entire driveline on the balancer and balance all the shafts as one unit. He ordered the required extension for his machine and called me when it was ready to go. Once he got the entire shaft on his machine, he twirled it at the rpms where I like to drive which is 62 mph. He was able to balance it in a jiffy. He put the driveline back in my vehicle and we tweaked the vertical distance spacer between the 2nd and 3rd driveshaft and now it 99% better.
If you do have a driveline balancing problem and your Ford dealer is willing to help, they will likely send your driveline out to a specialty shop that just works on drivelines because they don't have a balancer on premises. They don't see this often enough to justify it or keep personnel trained to use it. Make sure this specialty shop can balance the entire driveline. My Ford dealer was going to send it to Mobile. I called the Mobile shop there and they told me they would balance shaft 1 and 2 and then 2 and 3. This wouldn't have worked as noted above and would have been a waste of time and money. Consider asking Ford for spacer plates. My dealer gave me 4 when they attempted to fix it and we ended up using 3.
My previous post probably has the repair cost and I think it was less than $300??? Not too bad considering I was going to sell the RV if I couldn't get this fixed to my satisfaction. It was really bothersome to me although the Ford tech who test drove it said he fixed it when he balanced the tires. If you are planning a trip to the panhandle, I'll fix you up with the guy who did mine. He was extremely helpful.
Good luck getting it fixed. Mark
