Premature Tranny Wear Due to O/D??????

[AmericanZ28]

I was talking to a girl friend the other day about her car, and she mentioned to me that she was driving her car with the Over Drive off (mid 90's Mitsu Galant) because she heard from many people that it is bad for the tranny. The advice ranged from friends to a supposed experienced "Mechanic."

I explained to her how all that O/D is, is an extra gear in the transmission to help save gas by transfering less engine speed (RPM) to more wheel speed (MPH). More MPH per less RPM = Better gas milleage, and less engine wear and tear. Another discussion was about manually downshifting the car on steep hills. I explained that being an automatic, the transmission will downshift for you (through TPS position and speed) by simply applying more pressure on the throttle.

Needless to say, she was still a little hesitant to accept my "theory," so I decided to post it here and then later turn her on to this thread and get the truth from some real experts! So chime away, and correct me if I'm wrong! Thanks Guys!

[Z Ya Later]

Sounds right to me. Granted its not the same vehicle, but in the owners manual for my Jeep, it states "to downshift vehicles equipped with an automatic transmission, press the gas peddle down until the transmission shifts down." She needs to understand that the shifter in an automatic is not the same as the shifter in a manual. Unless you have a manual valvebody (like Fred and some other members have), all you are telling the transmissions is how high a gear to go to. In fact, on electronically controlled transmissions, it can be bad to hold the transmission on a lower gear when it is ready to shift up. Hope this helps.

[AmericanZ28]

Thanks for your input Steve, keep em coming!

[Steel2686]

Here's my take...

I've always used O/D when I know I'm going to be traveling at a certain speed for longer than say, a mile. If my trip takes me through a high traffic area, or an area with several stop signs and lights, I just keep it in drive so the tranny isn't doing any unnecessary shifting.

Otherwise, O/D is there for a good reason.

[Dave M]

agreed, O/D is there for a reason. It's nothing more than 1 more gear. It will do no harm to the tranny, and will save considerable wear and tear on the engine at highway speed. If it's a 4 cyl and 4 speed, think how high that engine is revving in 3rd gear at highway speed! Even a V6 will be spinning like wild to keep that car moving at highway speed. She's throwing money out the window by not using it.

As for downshifting, the only time you should have to do that is if your car is overloaded and the weight is pulling it faster and faster down the hill and yur brakes are in danger of not handling the prolonged heat. That's why large, steep hills have trucks downshift prior to going down the hills. But this really shouldn't be an issue with cars unless your towing something or very overloaded.