Tired Wipers
Q:I have a 1996 GMC Sierra, and when I use my intermittent wipers, they sometimes stop in the middle of the windshield for a few seconds. Is this a sign that the wiper motor is starting to go, or could it be something else? My truck has 114,000 miles on it.
A:It's probably not the motor itself, but close. Start with a call to GMC at 800/462-8782. There's a recall in effect, referring to intermittent or completely inoperable wiper motors on a large group of 1994-1997 GM trucks, SUVs, and minivans (Recall #03023). Make sure you have the truck's VIN handy when you make the call. The defect involves cracked solder joints at the controller circuit board, attached to the wiper motor. If your Sierra is on the list of affected vehicles, any GMC service department should replace the circuit board at no charge, with no time or mileage limitations. If your particular pickup isn't on the list, or records show the recall repair was already completed, the problem may lie elsewhere, but the circuit board would still be high on the list of potential causes.
Ford Rearend Chatter
Q:I have a 2002 Excursion with the heavy-duty tow package, 7.3-liter diesel, and limited-slip differential. At about 25,000 miles, I heard a chattering noise while accelerating into a turn. It was notably worse with a 2000-pound trailer in tow. I took it in, and the dealer replaced the differential pack. Ten thousand miles later, it started up again. I took it to another dealer, who added a friction modifier to the rearend. It worked its way in and the problem subsided after a few hundred miles. Now at 44,000 miles, it's doing it again, albeit less than before. I went back to the dealer, who was again advised by Ford tech support to add the friction modifier, but mentioned that some chatter is normal in Excursion and Super Duty rearends. I tow about 10 percent of the time and only at about 40 percent of the truck's rated capacity. What's going on here?
A:Every clutch-type limited-slip differential has the potential to chatter on turns. While driving straight ahead, it keeps the two axles locked together to improve traction. The clutches are calibrated to break free and slip at a specified torque and allow the two wheels (or two pairs on a dualie) to rotate at different speeds when making a turn. Occasionally, the lubrication property of the rear axle fluid breaks down, causing the smooth slip to become a stickier chatter. Each individual rear axle design is more or less prone to the condition, and your extra-large SUV seems to be at the top of the list. I wouldn't be all that concerned, but here are a couple of items to keep in mind. First, ask the service department to determine exactly which rear axle your Excursion has. The book shows several choices, but most Excursions use the Ford 10.5-inch rear-axle assembly with the Traction-Loc differential. This unit should use nothing but SAE 75W-140 synthetic rear-axle lubricant after the installation of Additive Friction Modifier. Another axle may require a different grade lubricant. Immediately after service, you or the technician should go to a parking lot, cut the steering wheel all the way in one direction, and do about 20 circles, then cut it the other way and do 20 more. This is the best way to work the additive into the differential's clutch material. Ford considers a slight chatter noise on slow turns after extended highway driving an acceptable characteristic with no detrimental effects. If service quiets things down, go through this process when necessary.