HEEELP! Vibrations driving me nuts

[Leadfoot]

Background 78 K10 no lift running 350/th350/203 10F/12R.
I bought the truck a little over a year ago for D/D and plowing. When I first got it, it had a few leaks and vibrations. I changed the yokes on the t-case and rear pinion and put new u-joints in driveshaft (and had a shop balance it). The vibration was gone........
Now... after having the tranny launch on me (rebuilt) and rebuilding the 203 (while it was out), at some point this winter I developed a nasty vibration at about 65MPH. I have tried running the truck in 2nd gear to see if the vibration occurs any differently but it doesn't, which would lead to it being speed related rather than RPM related.

At first I thought it was an out of balance wheel/tire (as everything else should be fine), but I just swapped out wheels/tires (I have one set for the summer...Bling/Bling, and one set for plowing in the winter), the ones I had on there were 31 x 10.5 R15 "mud terrains" and the new ones are 31 x 10.5 R15 "all terrains". The vibe is still there (same speed), but it does "seem" to be more noticeable.

I am planning:
To have the driveshaft checked AGAIN (out of round and/or out of balance)
Rebalance the tires (don't think that's it)


The question is would something else cause this?
Tranny/T-case
Drums
Could an axle be bent?

Any help (or past experiences) is GREATLY appreciated as this is driving me nuts. A heavy vibration at cruising speed on a daily driver, can get old real QUICK!! /forums/images/graemlins/angryfire.gif

Thanks in advance.

 

[DukeBoy88]

You've eliminated most of my guesses. does the vibration go away or blend into the background at a higher speed?

 

[monte0172]

Is the vibration in the steering wheel or in the seat? This will eliminate front or rear depending on which it is. If its in the seat then i would suspect an out of round driveshaft. Like you are already thinking.

 

[georgiared84]

The speed kind of caught my attention . Mine does it at exactly the same speed. I went through almost the same steps. The only thing I can think of is the fact that my rear carrier is so loose. It has a lot of side to side play in it as well as a lot of play in the spiders. I'm just going to replace the rear because I've already put new bearings and shims in this one before.

 

[Leadfoot]

The vibration seems to stay (at least until 80 as I do not dare go any faster with it like that....and actually I only went that fast while it was vibrating to see IF it would go away).

The whole truck shakes, so the steering wheel does too, but it does not feel like the steering wheel is shaking (hand seems steady) independently or more so than the truck, so I don't "think" it's front end, but the plow lights do seem to dance quite a bit, so who knows.

Also to add, I checked the fluids (tranny, t-case, and differential and they all are topped off....didn't need to add any).

 

[monte0172]

Well according to what you just said its more than likely in the rear end or atleast transfercase back. When its in the front end the steering will shake noticably and when its in the rear end the whole body will shake but you wont notice it in the steering as much. This should at least give you a starting point. Driveshafts being out of round are a real good cause of this at the speeds your talking about. but they usually wont go away at all they just seam to get worse the faster you go.

 

[toynova]

Check the tranny mount. Mine came loose any it felt like a wheels where ready to fall off. Shook the whole truck!