I have a 2012 FX2 EB. When it was fairly new, I had an issue with the SY clunk. Took it to the dealer, diagnosed and fixed.
Fast forward 3-4 years.
About 2-3 months ago, I noticed a clunk again.
Took back to the dealer (on my nickel this time). Diagnosed as SY again and repaired.
Driving home, clunk is still there.
Took it back the next week. They diagnosed SY again and said the first repair was faulty.
Drove for a day or two and clunk returned.
Took it back a third time yesterday and got the "Can't duplicate issue" response.
Picked up the vehicle and told them I would never be back and won't likely consider Ford again when time for new vehicles, since they are the only convenient Ford dealership for warranty work.
I still need to find someone to fix the issue, but I am tired of dealing with it right now.
I won't be able to take it very long, as I am **** about things like this. I wake up at night thinking about that clunk. LOL.
Question is, it doesn't hurt to drive with the clunk does it?
I know it "could" be something else, but I'm almost positive it is the SY and my dealership is a bunch of idiots.

 

Get used to it. Mine repaired twice. Service guy said "you'll be back". I just live with it.

 

So you've driven yours with the clunk for a while and it hasn't caused any other issues?
Thanks for the reply.

 

I have.. I got used to it... no other issues with the truck

 

I have 133k on mine, had the SY addressed at dealer along with other minor adjustments back in late 2012. The clunk has been back for 2 years, but no negative side effects as of yet!

 

I have a dealer that knows what they are doing, so they ordered an updated nickle plated 2 piece drive shaft to repair it and a yoke cover and have not had the problem since then. Thank god.

 

Had a 2011 eb 4x2 [2 pc drive shaft] being mechanically inclined having access to the tools I drilled and taped the the outer spline and installed a zerk then every other service [about 12k miles just give it a couple of pumps with a grease gun. Viola no more thunk clunk. noticed on my 2015 they changed the slip spline design should not be a problem.