A common fear among drivers is accidentally shifting into reverse while on the road, which many assume could be catastrophic for the vehicle. But can you really damage your transmission if you – or a curious passenger with a death wish – decide to switch from drive to reverse while driving?
If you drive an automatic car built in the ’90s or later, you probably won’t cause damage to the transmission, because the powertrain control module (PCM) in most modern cars simply won’t shift into reverse when you’re on the road. A mechanism called a reverse interlock prevents the gearbox from shifting into reverse, even at speeds of about 5 mph (8 km/h). This function is controlled electronically by the PCM in modern cars, while older vehicles used a hydraulic system to achieve the same effect. If you put your car in reverse while driving, the reversing camera may turn on (provided your car has one) and the transmission may shift to neutral, while the drivers behind you may be startled when your backup lights come on.
But if your vehicle’s reverse protection doesn’t work or if your car doesn’t have one, the engine will likely stall. In general, it is not a good idea to put your automatic transmission in reverse while driving as this will put additional strain on the transmission and could potentially cause significant damage.
What happens if you put a manual gearbox in reverse while driving?
Putting the car in reverse will likely produce a loud grinding noise, and if you manage to engage reverse, the engine will likely stall. Synchronizers in manual transmissions ensure smooth and precise shifting between forward gears, but reverse gear usually lacks a dedicated synchronizer. Shifting into reverse at high speed from a forward gear can cause the gears to collide, potentially damaging the reverse gear teeth and wearing out other transmission components. So it’s simple: if you drive with a stick, you’re going to have to use some muscle to get it into reverse while you’re driving, and if you succeed, you’ll probably end up with a huge hole in your wallet.
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