Picked up a used 2011 5.0 excab xlt 4x4 75k miles. Truck runs good. Only problem is a clunk from takeoff. Son laid on ground and can hear it from the rear. I crawled under and pulled on the driveshaft. There wasn't any play in it. I don't see anything worn. Rear isn't leaking. Any thoughts on what's causing it?

 

Grease the slip yoke.

 

Ditto. I think the official term is "slip bump". The ultimate cure is to replace the slip yoke. I got tired of greasing the '05 and finally replaced it about 45,000 mi. ago. No more bump.
-- Lube it first though. Apparently Ford has some kind of specific grease that's supposed to be a good long-term fix.

 

My son said he could hear that bump in the rear. Doesn't the slip yoke go into the back of the transmission?

 

It's probably manifesting through the rear end, but I'd wager that it's the yoke sticking. It's VERY common. My best description would be, as you tip into the throttle from a stop it feels like someone lightly bumped you from behind.

 

yes that's exactly what it's doing. Worse when I'm off road

 

 

Todd? What for

 

Drive shaft clunk. It's the slip yoke and is very common through a few generations of our trucks. Easy fix.

 

I have a 4x2, which means that it has the two-piece driveshaft. I just did the slip yoke service myself about a week ago and it has yet to come back at this point. It tends to be more common on the two-piece, but it has been reported that it can occur on the one-piece.

This is what you want to get. It was actually a couple bucks cheaper at my dealer believe it or not. Also be sure to have a helper available if you DIY.

Also refer to this TSB. It has good information and may help even though it is for the two-piece. I used the repair kit listed on the TSB (only for two-piece).
http://www.revbase.com/BBBMotor/TSb/...dPdf?id=177141