Hey guys... I need some help here... My truck just started to make a vibration that starts around 30mph or so. It's rattling my dash. I can feel it in my steering wheel also. It's not a death wobble thing cause it isn't HARD vibration but it's very noticible and I can hear some type of repetitive "whirrr" (sounds like maybe a tire but ?)
I have all the upgraded steering stuff and have greasable u joints in driveshaft that I grease every 3000 miles. I don't think it's any of that.
Here's the thing that worries me... It only does it when I'm on the thottle. In other words, if I accelerate from 50 to 60 mph it'll do it but if I let off the pedal it immediately goes away. It's not rpm related because I can put it in first gear and drive to 2500 rpms smooth as silk... I am worried. I have 80,000 miles on the clock. Original ball joints and hubs. I don't know why but I feel it's trans related.. so I checked fluid and looks/smells good. Temp never got above 177 on drive home. Power is still there. Oil level is good.
I am lost. Give me something to look for.

 

U-joint or carrier bearing if you have one. I had a vibration like that once and rebuilt the tranny, replaced u-joints, felt the carrier bearing rotate smoothly - but didn''t notice the rip in the rubber housing - until nothing else worked.....Dumb.

I'm not a expert on these things, but I've fixed more than one truck - OK - two.....

 

X2 on the carrier bearing

 

Carrier bearing and/or u-joints.

 

u joints in driveshaft are one year old and I don't have a carrier bearing

 

Well, if you have a single piece rear drive shaft, then I'm leaning towards the U-joints. Since you have eliminated the RPM related causes, you are left with the speed related rotating parts, IOW from the tailshaft of the tranny back or the output shaft of the transfer case forward. Time to pull the driveshafts and feel the U-joints. They can feel nice but when you drop the drive shaft and move the caps they can feel crunchy! Last, but not least, check the geometry on the one piece driveshaft too. Those U-joints need to be within a few degrees of spec or they will bind.

 

I just removed the front driveshaft. Before I did that I noticed seepage at the back of the front diff where the shaft connects. NEVER had this before and was just under the truck 2 weeks ago. Anyway, 85% of vibe is gone but I think that's because I don't have the connection of the driveshaft to the transfer case. I was also able to grab shaft and move it up and down at the xfer case...? I'm thinking whatever is bad (probably everything) in my front end was shaking the driveshaft so bad it fubar'd the front seal and bearing in the case. I was able to grab my front drivers tire at 12 and 6 and move in and out about 1/4" or so, then at 3 and 9, same thing. I'm thinking hubs, ball joints, and axle u joints... What say you?

 

Let's eliminate things first:
What kind of radial (side to side) play do you have in the front pinion?
Pop the front diff cover and check ring and pinion for wear/scoring.
Check the transfer case output shaft yoke. I'm not sure how much, if any, play you're allowed. You may be getting a vibration transferred up the driveshaft to the front diff. If you have access to a lift, get 'er up and let it run in drive with the wheels off the ground. Feel the trans and transfer case for vibration and noises.