Q: My 2002 1500 four-wheel-drive Chevy Avalanche with 110,000 miles has a vibration problem that came on rather suddenly. At 55 to 60 miles per hour, a vibration starts and by 65 mph feels and sounds exactly like driving over a rumble strip. I’ve replaced the U-joints on the drive shaft to no avail. If I had to guess, I would say that it seems to be coming from the front passenger side, but the whole vehicle vibrates. Putting the spare tire and wheel on the front passenger side didn’t have an effect. Recent work done at least three months before this problem included replacing the rear end fluid and the driver’s side front wheel-bearing assembly. Any thoughts on how to troubleshoot this?

A: The first step in troubleshooting a driveline vibration on a four-wheel-drive or all-wheel-drive vehicle is to confirm that all four tires are the same rolling diameter, regardless of what the alphanumeric tire sizing information says. Park the vehicle on level pavement with the steering straight. Put a chalk mark on the sidewall of each tire and on the pavement at the exact center of its contact patch. Roll the vehicle forward one tire revolution and mark the pavement at the chalk marks on each sidewall. Are all four chalk marks still at the center of each tire’s contact patch? If all four tires are not very closely matched in rolling diameter, the vibration may be caused by a binding in the drivetrain. Also, the left front hub/bearing assembly could cause a vibration like this.

My ALLDATA automotive database pulled up service bulletin #02-04-21-005A, dated February 2003, pointing to the possibility of the front axle being locked up or binding. You mentioned that the rear differential lube was changed — how about the front differential? Check that the proper gear lube was used. It should be synthetic 75W-90, not 80W-90 GL-5.


Q: My wife has a 2001 Hyundai Tiburon with 98,858 miles on it. Last time I changed the oil, I noticed that the power steering fluid level had reached the “add” mark. The owner’s manual tells me the recommended fluid is PSF-3, which is apparently no longer available. My local Hyundai dealer only carries PSF-4. The dealer would not confirm if the two fluids were compatible together. There are several power steering fluids available that say they’re recommended for all power steering systems. Is it OK to use one of these?


A: It appears that PSF-3 was the equivalent of Dexron II ATF, which has been superseded by Dexron III ATF, which should be compatible with the fluid in your Tiburon. The PSF-4 is a synthetic fluid that would be comparable to a synthetic ATF. A complete flush and fill of the power steering system with the PSF-4 would also work. Personally, I’d just top off the system with Dexron III ATF.


Q: I have a 2005 Mercury Sable with 15,000 original miles. Over the years I have had to replace the battery four times. If the car is not driven for three or four weeks, the battery is completely dead. This leads me to believe I have more than bad luck with batteries. How does one find a parasitic circuit that is draining the battery?


A: I’m not so sure you’re having bad luck with batteries. With so many computers, modules, keep alive memories and electronic systems on today’s vehicles, the typical parasitic current drain is in the neighborhood of 30-50 milliamps (.030-.050 ampere). While that doesn’t seem like much, if the battery is not fully charged to begin with, it’s unlikely this battery would start a vehicle after 30 days.

So, here are three suggestions. Drive the vehicle more often or for longer periods of time. Connect or hard-wire a battery tender/charger to the battery and plug it in while the vehicle is parked. Or — and this is less convenient because of the loss of all radio presets, etc. — install a master switch on the battery and disconnect the battery while the vehicle is parked.