Drivetrain slack?
 

Does anyone else have what feels like drivetrain slack? Any cure? Im tired of all the clunking.

No slack or clunking on mine. Does the clunking occur when you are going from acceleration to deceleration and vice/versa?

Yep it does.

When I put my truck in park and take my foot off the brake it seems like it rolls a good 6 inches, drives me crazy.

I have it. Had the dealer check it and they said everything was tight. Bull. I'm going to gripe and have them check again. Towed my fw this week and it would even clunk changing gears sometimes. Something is wrong.

lol wife guided me into load up her sled at the shop last winter, guided me right up, 2inches away from the ramp. Tailgate was down, put it in park, took my foot off the brake and BAM! ...Drives me crazy too

That's why the vehicle is equipped with a parking brake ... it is to be used EVERY TIME you park the vehicle.
It's not an "Emergency Brake" ... I'm not even sure what good it is in an emergency.

Not alot of things it could be -

- U-joints - Most likely
- Transmission - Not likely
- Rearend - Possible but not as likely as U-joints.

this
Bad U-Joint - YouTube
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Look at you, Johnny on the spot with the videos!

I was looking it up when you posted...still pretty strange to have a u-joint go so quick, but there's always a chance for a defective one.

Great minds think alike I suppose.

:-drink
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Fords drivelines have notoriously clunked over the years, the splines on the slip yoke may need to be greased (regreased) with this stuff:

Motorcraft XG8 PTFE Lubricant (Amazon $7)

Procedure can be found here:
2004 F250 Slip Yoke Service

The parking/emergency brake is a cable connection to the rear wheel brakes. Everything is separate from the hydraulic braking system so that if the hydraulic system fails you would still have the "emergency brakes" which would be a little better than "no brakes".