[Yachts]

On the way home today. I noticed a vibration. Happens around 1400 rpms in any gear, BUT only if the the pedal is mashed all the way to the floor. If it starts to vibrate and I lift the pedal vibration stops even if I'm at the same rpm..  Any ideas.. Richard  think it could be u joints like 512?

[Ozarkguy]

Drive shaft u joints.. For sure...

[Richard]

No. U joints will vibrate at a certain speed. The fact that it vibrates at a given rpm in any gear play Nya to engine

[Yachts]

But what's weird is at that rpm it only vibrates if the throttle is on the floor. If it's not no vibration

[Ozarkguy]

Here's a little info:
One of the most common signs of a damaged or bad universal joint is when a clunk is heard when the transmission is shifted into gear or moved from reverse to drive. This clunk can be caused by other problems but may be a sign of excessive clearance in the u-joints.

When a driveshaft flexible joint is on its way out it can also cause vibrations at higher speeds. This may feel like a wheel balance problem. A way to tell the two problems apart is in most cases a worn u-joint will cause vibration during acceleration or deceleration. A tire balance problem will create a steady vibration regardless of throttle position.

[lbrachfe]

my tranny was clunking like crazy when shifting into first or reverse after a transend fluid change for about 1000 miles 3 years ago and again after being stored for four months 2 years ago and this time only for the first day of driving and only when manually shifting (pressing the button). It has been smooth as silk since then. Was told that it was not unusual for that to happen in both the situations according Allisons tech line.

Also I wanted to mention that when I greased my chassis last year the U took an entire tube of grease. In fact, I used about 6 standard size grease tubes both times I greased all the zerks.....

[Richard]

Guys. Marc is saying it vibrates at 1400 regardless of gear. I am sorry but that is not likely the driveshaft. I would suspect fouled injector first since it only does it under full throttle. Take it to cabin and have them read the codes. If it is a main bearing or other internal you want to address it now not when it fails

I had a u joint problem. The give away is th vibration was at 60 to 65 mph in 5 or 6 gear. It did not track with engine rpm.

[Yachts]

One additional note. The vibration began after filling up with fuel and water so I was heavy.

[folivier]

Just filled up with fuel? Check your fuel filter and probably change it to make sure it's not clogged.
How low was the tank when you filled it up? Could have stirred up some crud at the bottom if it was pretty low. Again change the filter and see if that helps.

[Yachts]

Hadn't thought of that, the tank was at 1/4 full and I filled it up. I'll check fuel filter...only thought why was it only at that rpm..?