Towing a car while its manual gearshift is locked in reverse? We can all agree that's a horrible idea, right?

Dear Car Talk

Dear Car Talk | Dec 01, 1993

Dear Tom and Ray:

You guys are pretty good at trouble shooting auto problems, but I want to find out just how good you really are. Would it harm a car engine to tow the car forward while the manual transmission was in reverse gear? I know the answer, but unless you want to deliberately embarrass one of your readers, you won't ask how I know. In retrospect, I'm not really surprised about the consequences, but I am surprised that it happened in only a half-mile and at low speed. Even though I am hard of hearing, even I could tell that the little car (a Geo Metro being towed behind a 34 foot motorhome) was protesting mightily. Can you explain to me exactly what I did?

RAY: You goofed big time, Robert. When you're driving a car, the engine turns, and that makes the wheels move. But when you tow a car in gear, the opposite happens. The WHEELS make the ENGINE turn.

TOM: And since your manual transmission was in reverse, your wheels were making the engine turn backwards!

RAY: And engines aren't designed to turn backwards. When they do, what will often happen is that a loose timing belt will jump a few teeth, leaving the valves opening and closing at the wrong times. Then, when the pistons come flying up, they smash right into the unsuspecting valves. The result--like my brother--is not pretty.

TOM: That's probably what you did, Robert. Fortunately, it was only a Geo Metro, so you only crushed the valves on three cylinders. Had this been a real car, you would have had four four or more cylinders, and it would cost you even more to fix!

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