I was wondering if anyone could help me diagnose a problem with my 2004 F-350, 6.0L FX4, SRW. Here is the problem. When the truck is cold and it is cold outside (< 60 degrees or so) I don't really see this problem, but when the truck has warmed up and the outside temperature is warmer the problem begins. The warmer it is outside, the problem is more pronounced. I have driven in the mountains for 6 hours straight recently and the problem stayed very mild (it was very cold out), but I can drive a short distance when it is hot outside and it becomes very noticeable very quick. The best I can describe it is as "drivetrain slack". When I am coming to a complete stop it feels like I get a little bump from behind, almost like pulling a trailer with a pintle hitch. Then, when I take off from a dead stop, I will get rolling and at after a couple of miles per hour and about 10 feet of roll or so, it feels like something catches up and I feel a little jerk, again like a pintle hitch getting tension or something in the bed rolling to the back of the truck. I have tried holding the brake just a little to see if I could take up the slack before I get rolling, I have tried taking off holding the auto transmission down in 1st gear and with the tow/haul engaged and nothing makes any difference. Any ideas or other things that I could try to solve this would be appreciated.

 

The most common reason for this is the drive shaft yoke.
The yoke develops a wear pattern and as the drive shaft moves in and out of the transmission this worn area moves up and over the splines in the outputshaft.
Most prevelant in take off and stopping.
You can try removing the shaft and applying some good grease to the yoke or replace it.