Q: I'm writing to you hoping you can resolve an argument I have with my mother. When stopped at a stoplight on red, I shift my automatic transmission into neutral so I don't slip the transmission bands. My mom says I shouldn't shift out of drive. Am I doing the transmission a favor by shifting into neutral, or does it matter? Who is correct, my mom or me?
A: Moms are inherently correct no matter the issue, right? And your mom is correct is this case, as well. First off, when your vehicle is standing still with the engine running in drive, it is not "slipping the bands." Transmission "bands," when they are used rather than clutch packs, are involved in the act of changing gear ratios. For example, a band may be applied to stop the rotation of one part of a planetary gearset while allowing another part of the gearset to rotate, thus changing the gear ratio of the transmission's output. None of these parts of an automatic transmission are turning when the vehicle is stationary.
The only part that is "slipping" is the impeller inside the hydraulic torque converter, rotating at engine speed. As engine speed increases, the impeller's vanes drive hydraulic fluid into the vanes of the turbine, which is connected to the transmission input shaft, thus moving the vehicle. There is no mechanical connection between the impeller and turbine inside the converter. All torque is transmitted hydraulically, at least until the torque converter clutch engages — but that's a question for another column.
So, after all is said and done, there's no reason or benefit to shifting an automatic transmission into neutral while at a stop. In fact, the only "slipping" that occurs is during the act of shifting the transmission into drive or reverse, and during the act of changing gears. Leave it in drive.
Mom's right, as always!
Q: I have a 2006 Grand Caravan with the sliding side door. This model does not have interior lever handles on the sliding door. The door can't be opened from the inside. Do you know where to buy the parts to fix this?
A: I'm truly confused. I checked my ALLDATA database as well as online sources and they all show an inside sliding door release button and handle on the upper forward edge of the door frame at window height. The button operates a release cable routed to the door lock mechanism at the rear of the door. If, for whatever reason, there is no handle and release button at this location, the handle, part number 0WL901D1AD or 0RT361D1AE, is available for under $70.
Q: I have a 2004 Cadillac Deville with about 100,000 miles on it. The "Service engine soon" light came on about 15,000 miles ago. he code that triggered the light is P0741, which indicates the torque converter lockup does not engage. Service agencies tell me that to fix the problem could cost $2,000. What's interesting is that I've driven the car about 15,000 miles like this. Am I doing any damage?
A: GM service bulletin #04-07-30-034A dated October 2009 points to the P0741 DTC indicating excessive slippage of the converter clutch. This could be caused by a sticky converter clutch control valve or clogged oil pressure screen due to sediment in the transmission fluid. Or it could be due to worn seals from slippage of the drive sprocket bearing inner race, an expensive repair that requires removal of the transaxle and replacement of the torque converter.
However, there are several less expensive options — the KISS principle — to try before spending big bucks. Add SeaFoam Trans-Tune to the fluid and drive the car for several weeks. If there's no improvement, a complete transmission flush and fill might help.
Converter clutch slippage in itself is not typically harmful, but if it is caused by leaking internal seals, the problem is not going to be self-healing.
Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.