Astro AWD vibrating front end at highway speeds

[JoeB]

I just bought a 1992 Chevy Astro AWD passenger van. 116,XXX miles, two owners, highway miles only, used for road trips by previous owners. Test driving the van I got up to 65mph with no apparent problems. When I left to go home (150 mile trip) driving down the interstate I start to get a shaking in the front end which feels like it orriginates on the right but could be both sides. It vibrates between 55 & 75mph intermintintly, feels like there are ripples in the road. I took it to Midas thinking it was a CV joint however they said CV joints were fine. The tires were replaced and balanced and the U joints were replaced. The guys at Midas took it for a test drive saying they got to 75 with no vibrating. When I left to go home which is 60 miles of extreme rise in elevation. It seems to vibrate when going uphill between 55-75mph again with acceleration. When I take my foot off the gas it goes away or is much better. The vibration was much much better after going to Midas but not fixed. Hoping it's not a problem with the AWD. Any suggestions

Register today for free or log-in if already registered to remove this ad!

[1Gary]

Joe,

Welcome to CF.

Two things to start off to look at:

Awd's MUST have matched sets of tires.I mean all four tires has to be the same.They will do some really weird things if not.

Astro/Safari's are hard on idler arms.If you need to replace them(do both at one time),replace them with Moog only.

Let us know what you have found with a update.

Thanks,

Gary

[MDTAHOE]

A vibration when accelerating only is typical of a inner CV joint. There is no way to tell by visually looking at them. Sometimes you can see it with the car in the air ( on a lift) in drive with the wheel turning. It is best on a alignment lift so that it can be racked from the control arms which pushes the wheels/ suspension to ride height.

[JoeB]

Thanks for the info

Yes all tires are the same, balanced, and air pressure is the same.

The mechanics said the CV joints were fine but is the 'inner CV joint' something different that they probably didn't look at?

Is it possibly an allignment issue?

Some other suggestions I found on other thread were:
* check motor mounts
* check front differential oil
* driveshaft is possibly out of balance
* replace front prob driveshaft
* check ball joints
* check A arms for play

Any comments regarding those suggestions?
Thanks

[MDTAHOE]

There is no way he could say they are 100% fine. All he can tell is the CV boot is not torn open. The front drive shaft is the second most likely thing. Bad motor mount car cause it but more typically on a front wheel drive car because it puts a bind on the inner CV joint. Ball joints and control arm (a arm) will not cause a vibration. Tie rods, idler arms, drag link and pit man arm will not either unless the are extremely wasted and there is no way the first shop could have missed that.

[JoeB]

Thanks....

I'll be taking the van in soon to try and figure out the problem. I have been suspicious that it's the CV joints from the beginning. I'll let you know what I come up with.

Joe

[1Gary]

Originally Posted by MDTAHOE

There is no way he could say they are 100% fine. All he can tell is the CV boot is not torn open. The front drive shaft is the second most likely thing. Bad motor mount car cause it but more typically on a front wheel drive car because it puts a bind on the inner CV joint. Ball joints and control arm (a arm) will not cause a vibration. Tie rods, idler arms, drag link and pit man arm will not either unless the are extremely wasted and there is no way the first shop could have missed that.

Big "A"-been around these Astro/Safari's for about 5yrs and have seen some pretty weird things on the AWD's.Idler arms being one of the weakest link in the front end components and given the AWD effect would shimmy at highway speeds.The shop he took the van gave him miss info about the inner CV's could have easily missed idler arms.Will be interesting to see what else he finds once he takes it to another shop.