Astro van Driveline Vibration

Have owned our 97 astrovan awd for last 8 years 130,000 miles , developed a driveline vibration 60 mph in the last couple years and cant seem to track it down, its a high frequency vibration that buzzes inside the vehicle can feel through steering wheel dash etc. changed the front driveshaft( rebuilt) no change. changed the front diff(Used) as it was running hot appeared bearings were going in it but no change. New front shocks seemd to help but just a bit Vibration dissapears if front driveshaft removed but driveshaft appears good, noise comes and goes related to driveline load pull trailer or boat seems to go away some especially when under load Only thing i can see is some minor and i mean minor movement in the front transfer case output shaft but i jusy cannot see that being a problem. it does not make noise or vibration if up on lift and run as speed as tried to isolate that way. the vibraton tells me u joints but man, they are next to new. Any thoughts from anyone who has had and solved weird driveline problems?

Take a look at the engine mounts . They was real bad about the engine mounts to collapse causing a vib.:HMMM:

Throw a stagger tape (thin tape measure) around all 4 tires. If they are all not within a half inch of each other it will make the transfer case rattle like crazy.

on the front drive shaft---is it put together with the u joints TIMED?

did the tire size thing as that was my 1st guess all good the driveshaft is a bolt onto flange setup pretimed when built (I hope) Am going to change the oil in the transfer case as have read the it can be a problem ,should be done anyways. Have been waiting for something to let loose for 2 years and 20,000 miles and nothing happened yet. Ive talked to a local gm w/a guy and he wished me luck as trying to track the vibration down on higher km units is really tough.

I've got one of these too. Changed front drive line, no difference. Rebuilt front diff, no change, Changed wheels and tires, no difference. I am running out of options. Van has never been wrecked. It is a high freq. vib. that sets up a hum in the floor, in front. Not front wheel bearing either, I changed them one at the time. I've driven it 16,000 miles with no change in the noise. I'm desperate and wishing a tree would fall on it.

It's a possibilty it's the lock up torque converter,I've had my go a few years back in my Astro.

In your initial statement you say that the vibration disappears when you pull the front driveshaft and drive in RWD only, so you have isolated the problem to the front axle assembly which is a major step. This rules out anything common to both front & rear, like tranny problems for example. My first thought is a front diff bearing (my rumble in the Jeep was a center axle carrier bearing breaking down), but you say you changed the diff with no change in vibration. Was it a complete differential swap, or just the center (thinking outer axle bearing here...) I would check your transfer case front output bearing. It is going to be "freewheeling" with the front shaft removed, but under a constant, varying load in AWD with the front shaft in place. You're going to have to crack the case and take it apart, or find a good off-road place that deals with TC's all the time. If you have not done regular fluid changes on your TC do that first - those AWD constant TC's need new fluid to be happy.

how much play is allowable where half shafts enter diff. There is some play there in mine and I have the same hum. Has anyone had this noise and actually fixed it? Mine does it even if I put it in neutral and coast it down in speed. The vibe goes away at the same speed as it would if it was in gear. With the front shaft out it improves but I can still sense a bit of it.
Thanks for ideas.

Does your rebuilt front driveshaft use u-joints instead of the original CV joints? My son had his original driveshaft go bad because the CV joint boot tore and let dirt get in and destroy the CV joint. He got a rebuilt driveshaft from Napa that used universal joints instead of CV joints. It vibrated like crazy. A new driveshaft from GM costs over $500 and the rebuilt driveshaft was about $200 but is was a POS. He returned it and got his money back. He lucked out and found a good used one at Pull & Save for $100 and it solved the problem.
Tim