Is it a good idea to downshift an automatic transmission while going downhill?

Dear Car Talk

Dear Car Talk | Nov 01, 1995

Dear Tom and Ray:

I drive a 1993 Ford Escort with automatic transmission. We live on a mountain. Should I shift down to 2nd gear when going down a steep grade? When coming up? My husband advises me to do so. But if it's a matter of placing extra wear on either my brakes or my transmission, the brakes would be cheaper to repair, wouldn't they? I ordered your "Ten Ways" booklet, but could not find the answer to this question in there. Thanks.

TOM: Gee, it's not in our pamphlet? Well, what do you want for a lousy three bucks, Joyce?

RAY: Actually, we agree with your husband on the downhill side. Putting the car into second gear--or even first if the hill is steep enough--uses the compression of the engine to slow the car down.

TOM: It does no harm to the engine OR the transmission. And it can actually save your life.

RAY: If you over heat the brakes--like you would by continually braking on a long, steep hill--the brake fluid can actually boil. And when it boils, the brakes stop working! Not good if you've still got more downhill to go.

TOM: So using the engine's natural braking action takes some of the workload off the brakes, and makes it a lot less likely that they'll overheat, and we absolutely recommend it.

RAY: On the way up the hill, you really don't have to worry about it. The automatic transmission will usually figure out what gear to use.

TOM: If the transmission is annoying you by constantly shifting back and forth between two gears ("hunting"), then shifting to the next lowest gear will keep it from doing that. But the annoyance factor is the only real issue on the way up the hill. Mechanically it really doesn't matter.

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