I have a 2000 XLT F150 4X4 and have discovered a vibration in the truck only when the throttle is lightly pressed,with no load on the enigne. I jacked the truck up and ran the motor in Drive(yes I did it safely),the transmission and drive shaft seem to jump and move upwards slightly when truck is engaged,thus I am thinking that the TAIL SHAFT that sits in the transmission case is worn,and moreso I crawled under the truck and gave the driveshaft a tug to find there is up and down/side to side play where the Tail Shaft and transmission meet.I should also note that the vibration is much worse when the truck is lighter in the rear ie no fuel in the tank compared to it being full.I also thought that the rear tires could be out of balance or worn but everything checked out fine by my observation.
So am I on the right path with my thinking or could there be a possibilty of something more wrong that will do more damage????
Anyone else have this problem???? HELP
Bye the way nice site,thanks for your time

 

I am a little confused as to when this vibration is happening......is it when you are driving? If so......around what speeds??

I'd check the tires first.....it is cheap and easy to have done. If that still persists I'd have the driveshaft balanced and checked for any possible bends.

 

Sorry for the confusion but it happens around 1500 RPM all the way up as long as there isnt any torque being put on the engine,as soon as a load is being created on the engine the vibration seems to dissapear or minimise.

 

So only when the tires are off the ground do you get a vibe?? Not when on the street??

If this is correct, then this sounds like a motor mount problem.....however I wouldnt worry about it since most of your driving is done witht he tires on the ground.

 

Hahaha good one,No this happens when the truck is being driven and you drive the truck normally and not accelerating hard or even mildly hard,just normal driving conditions....Mabey I should try to re-explain my way of giving my problem.
Under normal driving conditions I have a severe vibration,it starts at around 1500 RPMs as soon as I accelerate the truck the vibration goes away, as soon as I lift my foot off the throttle the vibration goes away, when I just filled up the truck with fuel the vibration seems to have minimized,it is still there but NO-WHERE near as violent.
I jacked the truck up off the ground and the tires seem fine as far as out of round,I noticed the tranny and driveshaft hopped when it was put in gear(Is this normal??)I grabbed the driveshaft with my hand and had free play where the driveshaft and tranny met.Is there supposed to be free play??The driveshaft on the other end has NO freeplay at the rear end.
I also noticed some scoring or polishing where the Tail Shaft runs into the tranny,I know there is a sort of dust cover that would created the effect I described but it almost seems excessive like it is wear.
Anyhow I hope this clears everything up....

 

There shouldnt be any play in the rear DS as this is a rear wheel drive vehicle......there will be some in the front.....

Since this only happens at certain RPM's and not at certain speeds, I'd say that it is not your driveshafts or tires.

It sounds like you might have a bad tranny mount. Lay under your truck on your back with your head facing the rear and attempt to bench press the rear end of your t-case.......if it moves at all then you have a bad tranny mount. I am not exactly sure of how the tranny mounts to any skid plates you might have.....but the tranny mounts that I have seen break had a rubber piece in the middle of two metal pieces and that rubber piece just split. This would give symptoms like you describe.

If this is not the case, then I'd check the motor mounts....you can suppor the weight of the engine at the bellhousing and remove the motor mounts to visually inspect them.

Hope this helps.

 

Hi Adrian and welcome to FTE

Good to see another BCer here too.
There is normally some play in the yoke at the front of the driveshaft where it goes into the transfer case.
Maybe crawl under another truck like yours and compare.
How are your U-joints? It doesnt take much to make a vibration like you're describing.