I have a lifted '05 FX4 with automatic. I've noticed for a while now that when I'm stopped or driving at a low speed and I punch the throttle even a little that there feels like there's a very slight slip in the drivetrain as acceleration begins. It's almost like there's a quarter driveshaft rotation worth of slack in the driveline. I know the diff gearing is good and it doesn't click each time you let on/off the throttle like a u-joint would. In addition, when I turn up the shift firmness using my programmer I can hear a slight, dull metal-metal thud that accompanies the "slack" and sounds like it's coming from the transmission/transfer case area. Any suggestions?

I was thinking it might be the tranny mount.. any simple way to check?

Thanks.

 

mine kinda feels like its gotta spool up to accelerate...is this similar to you

 

No.. this feels more specific. There's a distinct engagement point once the slack is taken up. It's almost like you are slipping a clutch just a little and then let off suddenly. Once engaged it's solid. There's also the dull thunk sound that goes with it.

 

Is that, by chance, how you ended up with the name Thump?

 

No.. that's due to my lack of creativity.

 

i have that same slack, minus the "thump", and its only after the truck has been driven for a few miles.

fyi, i had a new tranny installed 4k miles ago.

 

Mine does the same thing and I have looked and checked everything I know but I dont have a clue what it is.

 

A little further testing shows that I get the same result in both 2 and 4wd so I guess that isolates it to the tranny or transfer case.. anyone else with suggestions?

 

Im new to the forum and just bought an 05 FX$ and had similar problems so i took it in and they replaced the slip yoke and WALA!!! problem fixed, just throwing in my 2 cents!! good luck

 

Nice.. that sounds like a likely culprit. Especially considering mine is lifted. I'm assuming you're referring to the slip yoke on the rear output of the transfer case? If you don't mind me asking, how much did that run you?