Thanks so much! to the numerous posts regarding the mysterious clunk that can often occur with the Super Duty's upon acceleration from a stop and deceleration to a stop. I was able to locate the ever-annoying clunk as relating to weakness in the slip yoke exiting the transfer case. Upon removal of the boot covering the splines of the slip yoke leading to the driveshaft it became quite apparent that at (only..haha) 100K miles the grease that had originally been applied had run its course and been rendered ineffective. Unfortunately, with the substantial burden put on my vehicle by a large fifth-wheel, I found that the splines had been excessively worn, warranting replacement of the part.

After approximately $100 for the new slip yoke (from Ford) [along with drilling and tapping the new yoke for a grease zerk, thanks to advice from the forum] and some new u-joints, my truck accelerates and drives like a brand-new truck!! I also replaced the carrier bearing ($80) while I was working in the area (and it also did seem to alleviate some vibration that I hadn't really noticed beforehand!)

So if anyone is chasing the illustrious super duty clunk, hopefully this will give you some further advice as how to alleviate that oh-so-nagging problem. So far it's been the best $200 I've ever spent, as I like my truck twice as much with its newfound solidness (not a word, but it works )

 

Thanks for that great information.

 

No clunk yet on the 99 Super Duty (Now I know where to look!) - but the 95 Bronco has it bad

 

That's great.

 

BTW "solidness" is a word. at least in the Merlin Dialect it is.

 

Is this the fix you're referring to?

http://www.eurekaboy.com/f250/slipjoint.htm

 

Redsundevil-i had "the clunk" about a year ago and fixed by regreasing the splines, but now it seems it has came back, i am going to add a grease nipple this time, so i am wondering where exactly you put the nipple??

 

Ryan- That's pretty much the gist of the fix.

Bigred- I drilled and tapped for the zerk in the body of the yoke about an inch away fom the front of it. There is a nice flat casting surface there that seemed to be a good spot for it. I believe that since the yoke is hollow, you can put the zerk anywhere you like so long as you eventually hit the hollow area in the middle. Once installed, it took around 30 pumps with the grease gun to fill er' up, so these things need a lot of grease!

 

I'm glad you got your "clunk" fixed! The zerk idea is a good one but I would make sure you are not "overfilling" the yoke with grease. I'm not sure about the SD, but I had a total transfer case failure on another rig from hydraulic pressure created by overfilling a slipshaft. The thing acted like a hydraulic ram! I drove it for months after lubing the shaft and noticed a slightly rougher ride but didn't think much of it. Then I started getting a whining noise from the x-fer case and then about a month later I took the rig off road and did some heavy wheeling and the output shaft pushed through into the x-fer case!! I was crawling through a pretty decent hole and the right rear wheel and suspension fully compressed and BANG. The case even broke in 3 places big time! When I pulled the shaft apart the grease that had gone in the shaft DIDN'T make it's way one bit to the splines and was collected behind the shaft! I had some decent driveline angle from a lift and when this thing compressed and the shaft moved forward, the slip yoke couldn't take up the movement and my x-fer case absorbed it instead. It did some damage to the pinion as well, but I just live with it. When the rear differential get's hot, it pours lube out the pinion seal.

I now disassemble and grease all my slip shafts. I know it's a longer process, but worth it to me if it saves me thousands on broken parts. Plus it gives you a chance to look at the health of your splines and clean it while you're there.

 

This is what I used.

 

thanks redsundevil.

taylomade99- interesting information,thanks to you too

 

Thanks everybody for the great info! I have a "clunk" that I could not figure out too. Now I know where to try.

 

A lot of the newer yokes have a hole in the big end , to prevent the hydro-lock.

 

How about drilling one hole for the zerc, and another one for pressure relief?

 

There you go. In one end and out the other.