vibration in 80km/hr

Hi,everyone,
while I drive in the highway,once when the speed up to 80km,the entire car vibrate,just like someone shaking the car,in the city,drive ~60km no problem at all,would it be the tire not balanced?
I checked the tire,doesn't seem like lost any weight on the rim.
Any suggestion?
Btw,it's 97 3.3L with 150,000km.

Thanks in advance.

Try rotating the tires. See if that changes anything. Maybe you can better pinpoint the source of the vibe. Try rebalancing just the front set or the rear set first. When they rebalance the tires they will see if any are out of round.

If it's not tires, it could be the transmission. Find an open stretch of highway with no traffic closeby. Get up to speed and get the vibe going, then shift into neutral. If the vibe goes away, you may have found the source. That could include the torque converter. Don't shift back into drive until you slow down. Ideally pull off and stop then shift back to drive.

Other sources could be brakes or suspension. Try loading the van to it's max weight and see if that changes anything. If the vibe goes away or decreases, I would suspect weak rear shocks or front struts. Anyone else have some tricks?

Try rotating the tires. See if that changes anything. Maybe you can better pinpoint the source of the vibe. Try rebalancing just the front set or the rear set first. When they rebalance the tires they will see if any are out of round.

If it's not tires, it could be the transmission. Find an open stretch of highway with no traffic closeby. Get up to speed and get the vibe going, then shift into neutral. If the vibe goes away, you may have found the source. That could include the torque converter. Don't shift back into drive until you slow down. Ideally pull off and stop then shift back to drive.

Other sources could be brakes or suspension. Try loading the van to it's max weight and see if that changes anything. If the vibe goes away or decreases, I would suspect weak rear shocks or front struts. Anyone else have some tricks?

Thanks,RIP for your input.
That's what I'm going to do 1st is to check or balance the tire and it's just the time to switch back to summer tire anyway,I'll do them at the same time.

For the tranny,that's what I'm afraid of,I'll try your test and see what's the result would be.

For the brakes,I just replaced the front rotors and pads couple months ago,so I think I can rule out that.

Suspension,that would be another area to look at.

Thanks.

I had a 97 Caravan 3.0 3spd. with the same problem. Turned out to be the axle bearing in the differential. I found it by lifting the van and shaking the drive axles at both ends. The bad bearing was enough to allow axle to flex enough in the bearing to create the vibration. Surprisingly the was no bearing noise, just the vibration.

Good luck!
Ron

I had a 97 Caravan 3.0 3spd. with the same problem. Turned out to be the axle bearing in the differential. I found it by lifting the van and shaking the drive axles at both ends. The bad bearing was enough to allow axle to flex enough in the bearing to create the vibration. Surprisingly the was no bearing noise, just the vibration.

Good luck!
Ron

Thanks for the info'.
I'll check that too,hopefully just the tire,I'll cross my finger.