Posted: Jul 28 2010 at 3:18pm | IP Logged

that could be quite a few things, I do know whatever is wrong is pretty bad. 

Does the steering wheel shake with it too?  when you brake do you feel it shaking in the pedal?

Posted: Jul 29 2010 at 4:16pm | IP Logged

I would almost want to say that you have a bad bearing, or a bad U-joint.  I've got a feeling the truck will wander pretty easily if you just hold the steering wheel straight?

I can tell you that this is really bad and should get it fixed asap.

Posted: Jul 29 2010 at 10:47pm | IP Logged

..

In the old days we called it a shimmy. If it's a vibration and it's a 4x4 it might be a u-joint/CV joint but it sounds like the beginning of the horroble 'death wobble'. To little caster, worn steering links, bad ball joints, loose wheel bearings, or bad shocks are main causes. Tires bulging and out of round caused a wobble in our Sentra one time. Death Wobble happens often in old ridged axle front ends. 

Some times swapping wheels can 'fix it'.

Have a good one.. with two scoops!..  Don S..