My tracker is making an odd pulse at specific speed of like 28-35 mph.  I feel it in my lumbar and it feels like a fwd/rev power pulsing. It’s quite odd.  Doesn’t happen at higher speeds.  Not really a vibration more like a rhythmic pulse.  Any ideas?   I’ve tugged on all the joints and wheel bearings and I’ve unlocked the front hubs to manual. 

Look up u-joint oscillation.  I am not sure if it is the cause.

My previous rig did the same thing.  It would start low and gradually increase in amplitude.  The rig would basically bounce up and down. My shocks were much softer in that rig. My new one doesn't do it as much.

So you’re saying this is inherent to joint driveshafts and it’s not a problem?

I will let someone else chime in on that question.  It happens in different vehicles too.  I don't know at what point it should be considered a problem.

It may just be the shocks combined with the driveline angle.  My new rig doesn't do it, but my shocks are stiffer.

Interesting.  Can’t say I’ve ever noticed it in a vehicle before but that is what it feels like.  Maybe my joints are going bad but they pass the driveway tug n twist test.  Doesn’t seem to always do it either. 

When mine started doing it I searched for what it could be.  It seems to be an issue with certain full size trucks too.  I read about issues on all the major trucks.

I would check the u-joints.  Do you have any kind of clunk especially when stopping in the middle and taking off again?  It is easier to notice in automatics because you can find it by shifting directions on the flat.  When U-joints get really bad the broken up rollers can jam the other bearings making a twist/tug test inaccurate.  4 bolts to pull the driveline and really check them out.  (if you have much lift you may not even need to jack it to do it.

No clunks at all and smooth at all speeds except that 25mph and only sometimes.  I’ll get around to pulling the prop shaft but it’s not a priority right now.  I’ll wait until I’m on side of road long way from home to move it up the list. 

Samurai?

You may be experiencing the first stages of death wobble...

Drivelines maybe as well... Not a 'twist' test but look to see if the caps are discolored, there is any shininess like they've spun, do side to side 'wiggling' of each joint area.

-Eric