2006 2WD, 4.2l, open diff...120,000 km

I am chasing down an elusive highway vibration at 100-110 kph. Feels like driving on highway warning strips...not limited to front end or rear...its everywhere!

So far I have confirmed tires are good, balanced with road-force, driveshaft re-balanced and put in phase (was out). Hanger bearings and U joints are all good. Vibration does not go away if I slip into neutral.

Today I had the rear axle on stands and I noticed I could get some play in the axles (in/out)...pushing and pulling wheels toward diff.

Is this normal? How much movement would be considered excessive?

 

That's probably not it. There's usually noticeable end play as well as rotational. Sounds like tires to me. Do you always check tire pressure after somebody else touches the truck, like an oil change joint? They have a tendency to over-inflate tires. This results in multiple belt separations if not corrected before hitting a hot highway. Nobody will detect these separations but they will raise hell with your ride. I fought severe ride problems on a Cherokee for several years and nobody could fix it. Eventually I discovered that my oil-change joint was pumping my tires (not truck tires - basically car tires) up to around 50 PSI. I remember once getting the oil changed before a summer road trip down south on blistering highways. I never knew how close I was to a blowout - the pressures had to be 60 PSI. It naturally had a hard ride, but also had a shimmy that nobody could stop. No balancing or alignment really helped. I put a new steering stabilizer on it and several sets of good shocks, like Bilstein. Finally I decided to sell it, but the tires were pretty shot by then, so I put a set of BFG 'Long Trail TA' on it. When I drove away from the tire shop it was like riding on a cloud - what a transformation! Ever since that day I watch my tire pressures like a hawk. There's a good gauge in every vehicle and I'm checking pressures with every temperature drop and whenever somebody else touches one of them. There's something else about bad tires - they will cause uneven wear on brake rotors resulting in brake chatter, and you can't get rid of it. Every time you turn or replace the rotors, it comes back after a few thousand miles.
You can do a little test that might tell you something; temporarily and for testing only, reduce your tire pressure to about 25 lbs and test the vehicle. I think if you note ANY difference at all, it points to the tires.

 

Definitely sounds like it may be a tire. I would have said u-joints, but you said they are good.

How much play did you get when pushing/pulling on the axle? Some play is normal but anything like 1/4" is excessive.

 

Tire.

they can be ballanced perfectly & be egg shaped. Its amazing what a bad tire will do to you.

Take them off the truck & roll them down the drive way. I bet you will see the one that is bad. it will either wabble or fall over.