Constant gear shifting shortens the life of a transmission

BY Jim KerrBackyard Mechanic . Sep 29 04:00 am

Question: A few years ago we were in Quebec and the cab driver, when he came to a traffic light or any other lengthy stop, would put the gearshift into neutral. We asked why he did this and his reply was that it was easier on the transmission. Have any comment on this? — Harold

Answer: I assume the vehicle had an automatic transmission. An automatic transmission does place a slight load on the engine when the vehicle is stopping and idling in gear, so theoretically it would use a slight bit more fuel than shifting it into neutral. As for being easier on the transmission, shifting back and forth from drive to neutral constantly applies and releases clutches inside the transmission. This movement will cause wear on mechanical parts and seals inside the transmission.

Doing this occasionally would not make any significant difference in transmission life, but doing it constantly in a vehicle that does a lot of stop-and-go driving, such as a taxi, would shorten the life of the transmission. Your cab driver was sadly misinformed.

Perhaps the cab driver was mixing this up with manual transmissions. Placing a manual transmission in neutral and releasing the clutch pedal during extended stops will reduce wear on clutch bearings and thrust bearings for the engine crankshaft, plus you don’t have to hold the clutch pedal down all that time.

 

Question: I have a 2006 Dodge Caravan with a 3.3-litre engine. The air conditioning has not worked for several years. To fix it would require a new system, as it is not simply a leak-and-recharge issue as far as I understand, and to do a brand new replacement is quite costly.

I know someone who is getting rid of a 2001 Dodge Caravan with a 3.3-litre engine with working air conditioning. Would it be good value to remove the air-conditioning system from the 2001 Caravan and use it to replace the air-conditioning system in my 2006 Caravan?

Are there other alternatives to cooling the van’s interior? — Ellen

Answer: The first thing to find out is what exactly your Caravan needs to get the air conditioning working. Other than a leak of refrigerant, one of the more common problems is the compressor failure. This occurs because lubricating oil in the system flows with the refrigerant so systems low on refrigerant don’t get the lubrication to the compressor as needed.

When the compressor fails, metallic particles often are sent through the system, first to the evaporator and then to the flow control valve (thermal expansion valve, or TXV, on your Caravan). The metallic particles can clog the passages or prevent the TXV flow control valve from working properly. To fix this, the compressor needs to be replaced, the condensor needs to be flushed and filters need to be placed in the system to prevent metallic particles from getting to the TXV valve and back into the new compressor.

The system in the 2001 Caravan is similar but not exactly the same. The compressor and evaporator are interchangeable but the condensor has a different part number, likely due to mounting differences. Parts from the 2001 Caravan can be used to repair your 2006 vehicle but you will still need to have the system flushed and filters installed to prevent damage to the new parts you install from the other vehicle.

Depending on the cost of the 2001 vehicle and what your vehicle needs to be repaired, it may not be worth repairing the AC system in your 2006, but if you drive a lot and the 2006 is in good shape, then it may be worth repairing.

Because of the age of your vehicle, performing this repair is not a straightforward answer. It all depends on the cost of the repair versus how much you drive the vehicle.

james.kerr@sasktel.net