Questions and Answers

Chevy Express Driveline Vibration

Q. Hi! I am the proud new owner of a 1999 Chevy Express Van LS, with 23,000 miles on it. I bought it from a dealer's rental fleet, in very clean condition. It's a long-wheelbase 3500, with the typical options:

• 5.7 Vortex V8, 4-speed automatic transmission, 3.73 rear end
• Tilt/cruise, front & rear heat and A/C, power driver's seat, door locks, mirrors and windows
• 15-passenger seating
• OEM Firestone 245/75-16E tires

My problem is a drive line vibration. I feel it most at around 50 mph while under power, i e; maintaining speed on a mild grade. The feeling is reminiscent of the time I had a bad universal joint on my old Suburban- a mild, almost resonant judder.

My dealer's tech guy felt it too. He felt that it worsened when the lockup torque converter engaged, and suggested motor mounts and universal joints as possible culprits. The service department replaced a universal joint, without improvement. If anything, the vibration is now slightly worse.

I am wondering if you have any suggestions...
Steve

A. The only suggestion I can give you at this point is to remove the drive shaft and have it balanced. In the old days we used to use hose clamps to balance them, but that involved a lot of hard trial and error. Nowadays there are special machines that can balance a drive shaft in minutes. First of all, I would check and make sure the rear tires are in good shape and not out of round. Then make sure they are properly balanced on a high-speed wheel balancer.