My car the jerk...
I have a 1984 Chevrolet Celebrity with a V-6 engine and 100,000 miles. The car runs fine and gets good mileage on the highway, but when I start to reduce my speed on the exit ramp, the car develops a "jerky" motion. The "jerking" lasts until I come to a stop. When I move again, I still feel the "jerky" motion until my speed reaches over 35 MPH. What's causing this "jerky" motion?
TOM: I think my brother pointed out your car to me just the other day. There was a car in front of us bucking down the exit ramp, and my brother said "Hey, look at the jerk in that Celebrity."
RAY: Actually Adam, the trouble is in your transmission--more specifically in your torque converter. The torque converter takes the place of a clutch in cars with automatic transmissions. It separates the engine from the drivetrain with fluid so that the engine can keep turning slowly without turning the wheels. That's why you don't have to put your automatic in Neutral when you stop.
TOM: Since the torque converter works by "slipping," it makes automatic transmissions less efficient than manual transmissions. But at higher speeds (above about 35 MPH) some modern automatics have the ability to lock up the converter--just like a fully engaged clutch. When the converter is locked, and the slippage is eliminated, the car gets better fuel economy. Your car has this lock-up feature.
RAY: What's happening is that your converter is probably not un-locking completely when you slow down, so it feels like you're trying to stop a manual transmission car in third gear without disengaging the clutch.
TOM: Unless you have some unnatural attachment to this Celebrity and plan to pass it down as a family heirloom, your best bet would be to simply have the lock-up feature disconnected (actually unplugged). The torque converter will still work fine, and your symptoms should go away. You'll get slightly worse mileage, but at least people will stop talking about the jerk in the Celebrity.