What's the Worst You Can Do to Your Transmission?

Dear Car Talk

Dear Car Talk | Jul 26, 2016

Dear Car Talk:

My brother-in-law, who thinks that I am mistaken if my lips are moving, tells me that the worst thing I can do to my automatic transmission is start the car and immediately back out of my garage. His reasoning is that when the engine is warming up, it's running faster than usual. So when my foot's on the brake and I put the car in reverse, wham, the tranny slams up against wheels that won't move. What do you say?

-- Rolf

That's far from the worst thing you can do to your automatic transmission, Rolf. Putting bananas in it instead of automatic transmission fluid jumps immediately to mind.

Your annoying brother-in-law may have had a point 30 or 40 years ago. In the old days, when we had carburetors and mechanical chokes, you'd start up a cold car, and the engine would run at 2,500 rpm for the first five minutes. And sure, slamming the transmission into gear when the engine was running that fast wasn't exactly TLC for a transmission.

But now that engines are computer-controlled, an engine that's warming up will run at 1,000 rpm for 30 seconds, and then return to 750 rpm. So whatever strain you put on the transmission is minimal to nonexistent.

Plus, you're not going to sit there for that 30 seconds "straining" the transmission. Unless you have a garage fetish, you're going to release the brake and start backing up.

So tell your brother-in-law that he's wrong. That's far from the worst thing you can do to your transmission. Driving the car hard, especially accelerating sharply and suddenly, is worse for the transmission. And not only the transmission, but all of the other drivetrain components. Everything except the radio knobs -- they can handle hard acceleration.

So if you decide to pass a garbage truck and you pull out and put your foot to the floor, and the transmission downshifts three gears and your back gets pinned to the seat, you're shortening the life of your transmission, and the rest of your car, far more than you ever could by putting it in reverse in your garage.

And here's another thing that's worse than what your brother-in-law suggests: Backing out of your driveway and using the transmission to shift directions instead of stopping first. And don't forget about neglecting to change the transmission fluid when the manufacturer recommends. That often leads to bananas (see above).

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