My front end vibrates at speed

Question:

I’ve had a front end vibration in my 1999 Buick LeSabre ever since I bought it a year ago. It feels like a tire is out of balance, but it generates a vertical vibration on the dashboard and under the driver’s seat depending on its speed. It tends to manifest itself on the highway around 65 mph and gets really obnoxious around 75 to 80 mph or so.

I’ve taken the car to several shops and $1200 later I have new tires that have been balanced and rebalanced and rotated, and I had the discs and drums inspected to no avail.

Finally, I took it to a shop manned by graduates of the local tech school. I told the guy there of my problem and he immediately said that it was a front lower control arm problem that is unique to that model. He said it would cost me a grand and even then the fix “might” cure the problem. Well, naturally, I’m not going to throw a grand at a problem with no assurances that the car will be fixed to a degree that I can put this to bed. What I need to know from you is whether the shop is correct in its assessment or is there something I can do to get rid of this vibration?

I bought the car with 65,000 miles on the clock and it just rolled over 97,000 miles last week so you can see that I put on a lot of miles in a year.

Answer:

A number of GM vehicles, including certain Buicks, Oldsmobiles, Pontiacs,

and Cadillacs, manufactured between 1998 and 2005 had an issue with front lower control arms that caused or contributed to a vibration being felt while traveling at various highway speeds.

A technical service bulletin (TSB 00-03-10-007G) relating to at-speed vibrations in the affected vehicles was published by GM.

This TSB, however, specifies model years 2000-2005 Buick LeSabre and your car is a 1999. Also, the TSB specifically states, in part, “On Aurora, Bonneville, DeVille, Park Avenue, Park Avenue Ultra and Seville models, a newly developed hydro-bushing lower control arm with improved damping characteristics has been released. This control arm is not used on the LeSabre. The new lower control arms may provide an incremental improvement to the vehicle ride.” So based on this, I would certainly not recommend spending a thousand dollars changing the control arms in your LeSabre before looking at several other possible causes of the vibration.

Balanced tires can cause a vibration if something called radial force variation or radial runout is too much. There are several ways to measure this but the easiest is with a wheel balance machine that can do it. These include the Hunter GSP9700 Road Force machine and Coats XR1850 Runout/Balance machine.

As a rule of thumb, the radial force variation should be less than 18 pounds and ideally no more than 12 pounds. You can alter the radial force variation by moving the tire to a different position on the rim. If you’re unable to get the radial force variation low enough regardless of how you position the tire then the tire and/or rim should be replaced. Radial runout of each tire and wheel combination should not exceed .040-inches at the most and, if possible, should be less than .030-inches.

Another possible cause of the vibration in your Buick is bad rear wheel alignment. If rear camber or toe is out of specification, it too can cause a speed dependent vibration.

And, of course, don’t overlook the possibility of loose, broken or worn parts in the suspension. A bad bushing, CV joint, bearing, or other suspension part can cause a vibration. A bad engine or transmission mount can do the same thing. And though it sounds slightly crazy, it’s possible that any component attached to the engine can be the source of your problem. Many years ago I had a 1968 Z28 in my shop that had a speed-dependent vibration and after looking at, measuring, balancing, and/or replacing a long list of items ranging from the tires and wheels to the driveshaft without any success, I discovered that one of the alternator brackets was cracked. This allowed the alternator to swing back and forth quite wildly in a specific engine speed range and when it was violently moving back and forth it did so with enough force to shake the entire car.