Dear Tom and Ray: My son owns a 2003 Silverado 1500 4-wheel-drive Regular Cab Chevy truck. We hear and feel a loud clunk from the rear of the vehicle when starting from a stop. If you concentrate and go very slowly, nothing will happen, but if you take off from a stop normally, you feel as if someone has hit you from behind. The Chevy dealership has lubed the splines and given us a bulletin from GM stating that this is "Driveline Lash" and is normal in all newer trucks. We are wondering if you have heard of driveline lash, and is it "standard" in all GM and other makes of trucks? We will never be able to sell this truck if the prospective buyers feel a clunk. My husband says that it probably needs a new rear end and that the dealer does not want to go through the expense. The truck currently has 33,756 miles.
Ray: Unfortunately, driveline lash has been something of a trademark of GM trucks for the past half-century or so. It results from excessive slop in the differential, between the ring and pinion gears.
Tom: You usually hear it go "clank" when you go from drive to reverse, or vice versa. The noise comes from those gears slamming against each other when the drive shaft changes direction. The sound is then transmitted to the front of the truck through the hollow tube of the drive shaft.
Ray: But what you've got doesn't sound like textbook driveline lash. Normally, you hear it once when you drop the transmission into gear; you don't normally get it again when you start up from a traffic light. So either you've got a particularly bad case of driveline lash (in which case it will get worse and start howling), or it's something else.
Tom: Most likely the "something else" is a transmission problem.
Ray: Try this: Tell the dealer you're interested in his driveline-lash theory, but you'd like to drive another, similar truck to compare the two. I'm sure he's got another '03 on his lot somewhere that you can drive. If it sounds the same, you might be out of luck. In which case, just be sure to save the repair order in which you complained about the symptoms and they dismissed it as driveline lash. That way, should it get worse or should the transmission fail completely, you have a record of having brought it to their attention while the truck was under warranty.
Tom: But if the other '03 Silverado you drive does not exhibit the same symptoms, then you have a legitimate case to make that they need to fix your driveline lash.
Ray: Actually, your best bet is to be persistent but polite. If, in the end, the dealer won't help you, ask for an appointment with the Chevy zone manager. A zone manager has more authority, and might be more sensitive to seeing your follow-up complaint in the newspaper a few months from now. Good luck.