I have an 03' Avalanche that at 37000 Kms the rearend went out of it. Axles, Axle bearings, Crown and Pinion, side bearings were all changed. The drive shaft was also sent out to be balanced. Warranty ran out 2 months ago now with 53000 Kms and I now have another vibration in it. Mr Goodwrench first told me it was my tires and they need to be replaced, I didn't buy it and said it was in the driveline. After my own diagnosis I suggested we put tires off a brand new Avalanche and try it. This was done and the vibration was still there. I suggested they try the driveshaft which they did, still a vibration. They then said they would have another look at the rearend and found the side bearings were pitted and changed them. Took the truck out for another test drive, still a vibration. I am loosing my confidence in Mr. Goodwrench at diagnosing this problem. I think it is in the transfer case. Has any other Avalanche owners experienced this problem, if so what did it turn out to be? Any other thoughts? Also this is the 10th day they have had my truck! Really starting to loose my patience with GM Goodwrench!!

 

I've had similar problems in the past. Recheck the driveshaft to see if any of the weights have been thrown off. Going beyond this it is possible to have a torque converter imbalance. There is a problem that is hard to diagnoise, that is torsional vibration. This occures at low engine speeds with transmission in overdrive, especially with high geared axle ratios such as 3.23's. This condition is what you feel sometimes in a manual transmission when you go into high gear to soon, thus lugging the engine.
Check the u-joints and driveshaft alignment, especially with two piece driveshafts.

Hope this helps

westex

 

How bad a vibration?..noticeable?...

 

It was very noticeable. Believe it or not, I felt it in the steering wheel at between 45 and 55 mph. Anyway I changed the driveshaft and the vibration was gone. I always thought that a driveshadt vibration was felt in the seat/floorboard. I think that the vibration came through the steering wheel because the engine mounts and the rack and pinion unit are mounted on the same frame cross member.
I did the check to find it by jacking up the rear axle, (jack stands under the axle) removing the wheels and brake drums. Ran up to the 45 to 55 mph range. Vibration was there. There was no doubt about where it was coming from.
GM driveshafts are made mostly by American Axle & Machine, They are machine assembled , and the runout is really bad on many of these units. Mine had .055" behind the transmission yoke. Maximum should be .003". They counteract this runout by adding weight. My driveshaft had the most weight I have ever seen on a shaft. Which only proves you can balance a brick but it won't roll smooth.
BTW, the new draveshaft has a lot of runout too. It just doesnot vibrate. I think I will take it to a driveline shop and have it brought into spec's.

Regards

Westex