2002 astro vibration/shudder problem

saturnguy2 · 01-11-2007, 11:31 AM

Hi, I have a 2002 Astro that has developed a "shudder" problem mainly at speeds above 65 mph. The sudder isn't real bad but it can be felt in the seat and floor but the steering wheel remains steady for the most part. I have had the van to 3 different mechanics and had the service manager at the chev. dealership (friend of mine) try to diagnose the problem but no one seems to know what is causing the shudder. I have replaced the trans mount, U-joints, had the transmission checked and serviced, and new tires all around but the problem is still there, however doing these things seems to have made some improvment.
Any ideas of what the problem may be would be appreciated.

Blue Bowtie · 01-11-2007, 09:37 PM

RWD or AWD Astro? A transfer case on an AWD could be a problem.

saturnguy2 · 01-12-2007, 05:02 AM

Thanks for your reply, this is a 2 WD Astro.
This is the 4th Astro van I have owned in 18 years and this is the first time I've had a problem like this, and it came on suddenly.
I can't remember doing anything or haveing anything done to the van before this started.

jonsonton · 01-12-2007, 04:38 PM

Have you ever had out of balance wheels? Does it feel like that?

saturnguy2 · 01-12-2007, 04:56 PM

Jonsonton,
It's not out of balance wheels, I have had new tires put on, rotated them twice but no difference. I don't feel vibration in the steering wheel, it's more like a shudder in the seat and floorl

Thanks for the post.

CD Smalley · 01-12-2007, 05:03 PM

While at speed, no cruise control... and when the shudder occurs.... touch the brakes. Does the shudder stop?

saturnguy2 · 01-12-2007, 06:12 PM

CD Smalley,
The sudder starts to be more noticable when I reach 65 mph or above, it does not stop when I touch the brakes, it's still there when I use cruise control, the strange this about this is that it's been doing this since June 2006 and has not gotten any worse, in fact it's improved since I then. It's improved the most since I had the trans. serviced. The trans shop swears it's not the lock up torque converter or the converter clutch, but from everything I've heard, my opinion is that it is in the tranny somewhere.
My neighbor builds transmissions for a living, has been for over 15 years, he doesn't think it's the transmission either, but I'm still not sure. I don't want to just start pouring money into it in a trial and error mode, especially since I have driven it for thousands of miles and it's not gotten any worse or has not thrown a code for the check engine light to come on.

Thanks

CD Smalley · 01-12-2007, 07:53 PM

I wonder if you have the driveshaft in out of phase???

Anytime you remove the driveshaft you must re-install it in the same position. If you put it in 180* from where it was, it will vibrate like that sometimes.

Someting cheap to try.

Blue Bowtie · 01-12-2007, 08:21 PM

At 65+ MPH, what happens if you back off the fuel and move the trans into neutral?

saturnguy2 · 01-13-2007, 08:54 AM

CD,
How would I know if the drive shaft was put in it's original position?
Also, I purchased this van new and when this problem started the drive shaft had never been removed from it's factory position, it has only been removed once when I put new U-Joints in it.
An out of balance drive shaft had been suggested and I have never had it checked for balance, but there is no evidence that there is a weight missing.

Any other ideas?

Quote:

Originally Posted by CD Smalley

I wonder if you have the driveshaft in out of phase???

Anytime you remove the driveshaft you must re-install it in the same position. If you put it in 180* from where it was, it will vibrate like that sometimes.

Someting cheap to try.

saturnguy2 · 01-13-2007, 09:01 AM

Bowtie,
It seems like we tried this once and the shudder did not go away but I will try it again and see what happens.
If the shudder stops it would seem that it could be in the drive train but if it is still there it would not make sense to me that it would be in the drive train, rather somewhere in the wheels or front end.
However, all of the mechanics that drove the van seem to think it is coming mostly from the rear of the van.
It's really hard to tell where it's coming from, but like I have said, it seems to have improved since I had the trans serviced leaving me to think it could be in the tranny. My neighbor who builds transmissions for a living put his scanner on it and everything showed normal. He does not think it is in the transmission. I'm not sure he is right but I really don't want to start putting a lot of money into the transmission on the chance it might be. After every other possibility has been eliminated I may not have a choice but to try that.

Thanks

Quote:

Originally Posted by Blue Bowtie

At 65+ MPH, what happens if you back off the fuel and move the trans into neutral?

CD Smalley · 01-13-2007, 09:21 AM

As far as knowing by looking, most likely you can't. If I remove one I always scratch the driveshaft and the differential with an awl or mark them with a Sharpie so I know where to put them back.

I had a similar problem on my 9C1. I took the driveshaft out and had new u-joint installed and had it balanced. That fixed it for me.

Aren't there counter weights attached to the rear drums? Oh wait, does your van have rear discs or drums?

Blue Bowtie · 01-13-2007, 10:57 AM

Should be rear drums.

If all else fails, it may be time to strap in a transducer and frequency counter, or at least a harmonic reed tachometer to indicate the range of vibration frequencies. That can help determine if the problem is in the wheel/axle or driveshaft/transmission.

saturnguy2 · 01-14-2007, 07:40 AM

At 65+ MPH when I take my foot off the gas and put the transmission in neutral the shudder does not go away.
I'm beginning to feel it at lower speeds also although not nearly as bad.
Could it be something in the front end?
Could it be bearings? Front or rear?

Blue Bowtie · 01-14-2007, 08:24 AM

If the vibration feels like it is happening 12-15 times per second, it is likely due to wheels, tires, or something related to axles. If the vibration feels like it is happening 60 or more times per second (more of a "buzz" than a "shake") it is more likely related to the transmission, driveshaft, or torque converter. It may be difficult to determine this just by seat-of-the-pants feel.

Another thing you can do to eliminate the torque converter is to run the vehicle in DRIVE instead of OD. If the vibrations occur at the same speed ranges, it is not likely a torque converter or transmission issue.

Verify that the front wheel bearings are packed and preloaded correctly. Check the rear wheel bearings for radial and axial play (there are side gear shims and a few thicknesses of "C" clips available to adjust axial play).

Inspect the tire carcasses closely for sidewall or tread bulges (I'm seeing this a lot more in new tires, and it is supposedly "normal") or signs of tread squirm.

If you can raise and securely support the vehicle and reach the same indicated speed, you may be able to determine if the tires themselves are at fault.

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