Does anyone have an Astro that runs without vibration at 60-90 mph? I’ve an 87 Astro with strange vibration problems that I can’t solve. I’ve read all post in the forums and I’ve done the following:

- Changed tires and wheels
- Changed drums
- Balanced the driveshaft
- Checked yokes
- Changed the tailshaft bushing.
- Changed shocks

The van runs smoothly up to about 50-55 mph then it starts to vibrate, not always, but very very often, it seems to depend a bit on the roadsurface. It doesn’t change at all if I let off the throttle or accelerate when it once has started. I’ve run the van jacked up to try to figure out where the vibrations come from but so far without success. It’s seems more like some ‘bouncing’ from the rear, like if the fibreglass leafsprings are undamped or like if the van comes into resonance frequency with the roadsurface?

Could bad axleshaft causing this? I’ve never had this kind of problem with any other car or van before without being able to find the problem.

Any help is appreciated,
Tony

Does it change if you put it in neutral or even kill the engine? Just something to try if you haven't allready.

Motor Mounts can sometimes go bad, and vibrations can resonate through the frame. Try taking the van up to speed in 3rd (not overdrive) to see if the a different engine speed affects the vibration.

Thanks for advice. Running in third or fourth gear or putting the transmission in neutral doesn't change the vibrations/bouncing when they have started. Slowing down below 60mph makes the problems go away or sometimes (but not often) the vibrations disappear if I go faster.

Accelerating hard (WOT) up to 80 mph is the easiest way to produce the vibrations which start at about 65 and increases until I slow down to 60 mph. If I then accelerate slowly I can speed up again with only slight vibrations. It also seems to have a lot todo with the road. Sometimes I even think that the problem is totally gone for a few miles and then it's back again...

I've checked the idler arms and the steering linkage and it's okay. I'm pretty sure that the problem is in the rear end or motor/transmission mounts. But I can't figure it out.

Read something about doing an electronic frequency scan to find out what mechanical part are running at the peak frequency when the vibrations are severe. Don't know about any shop that performs that kind of test where I live (Sweden). But perhaps there are some equipment that a homemechanic can afford, I don't know yet. Somekind of sensor, a PC and software might do it.

After reading through the other Chevy forums I found that vibrations at highway speed seems to be quite common, unfortunately.

Tony

How old are the shocks? What are you doing taking a minivan up to 90mph?

How old are the shocks? What are you doing taking a minivan up to 90mph?

I'm running Rancho RS5000 shocks in the rear and they are about three years old. Perhaps they can be to hard and cause the bouncing and vibration at high speed or at least make the van more sensitive to vibrations? I can't remember though that the van lost its smooth way of running when I changed to the Rancho's.

About speed I would say that 75-80 mph is normal highway cruising speed in Sweden. I know it isn't a sportscar (I got a Corvette 1965) but still it should run smoothly without vibrations as I see it.

Tony

Two suggestions come to mind, 1.) Find a tire place that can check the wheel balance on the Van. I had this problem while in Florida with my 94 astro. They had a machine that would sit under the tire and spin it at varying speeds until they found the problem. They had to shave both my rear tires (to remove high spots). After spending $400 on front end repair/Alignment, They finally broke out this pc of equip and fixed the problem by shaving the tires. I'm now told by varying sources that the problem is common among aluminum rims. 2.) Take it to a shop that can do Hi speed tire balancing. Most of the tire balancers here only run at about 45 mph when checking the tires. Hope this helps....