I was the designated driver the other day and was driving some of my overly sensitive friend’s home in one of their cars. I pulled out of the driveway into the street and then went along on our way. But, apparently I had made a grave sin in the eyes of my non-technically inclined, non-car enthusiast friend. That sin was that I didn’t come to a complete stop before putting the transmission into drive… I haven’t heard the end of it since.
Now, it’s not like I was racing in reverse and then slammed it into drive like some sort of stunt driver. I was backing out normally, braked to less than a mile per hour, and then put it into drive. It was a very smooth transition and there were no clunks, bumps or any drama at all. If I was going any slower, I would have been stopped.
The problem is that most people don’t understand how an automatic transmission works. I believe they think that gears are actually moving into one another and that if you’re not completely stopped, you would grind the teeth off the gears. As you probably have guessed, this is not the case.
Automatic transmissions use a planetary gear set which have gears that are always meshed. Shifting gears happens by locking and unlocking the various orbits; and when not in gear, those orbits are left to freewheel. Locking these orbits is done by clutches and bands (basically brake shoes with friction material on them) which are activated by hydraulics. These clutches and bands are made to slide a little when engaging, and that’s that gives smooth shifting.
Furthermore, automatic transmissions need a method to be in gear and be able to have the car stopped without stalling the engine. This is achieved by using a torque converter which connects the engine to the transmission though a fluid coupling. The torque converter works like an egg beater mixing thick pudding in a bowl: if you beat the pudding without holding onto the bowl, the bowl will spin. But if you hold onto the bowl (like applying the brakes in your car) the egg beater will continue to turn the pudding, but the bowl (your wheels/transmission) will be stopped.
The transmission doesn’t get damaged when shifting into drive while the car is still (slowly) moving backwards because there’s no hard mechanical links between anything in the transmission. The slow engagement of the clutches and the slop of the torque converter absorb any speed differentials and allow you to do this. This ease of use of automatic transmissions is what they were designed for, and if this caused serious problems, you would hear about it all the time.
I’ve always wondered how a tranny works. Well here is something that possibly broke on my 99 expedition when shifted into drive and gas pedal pressed while rolling in reverse at about 3-5 mph. Since that incident at a tire shop by their speedy car mover @ speeds over 45mph there is a vibration/groaning sound around transfer case or front axle while slightly accelerating. Also won’t come out of 4hi or 4lo unless engine is turned off and cranked up again. I’m guessing its my transfer case shift motor.
Going from reverse to drive while moving slowly will not DAMAGE an automatic transmission, but it is a bad habit. The foreward clutches in your transmission are NOTa substitute for the foot brake, and wear and possible failure will result from chronic reverse/drive or drive/reverse shifts while car is in motion.
I’m thinking you nailed this one right on the forehead, sir. Just like many other bad driving habits, they might not break the car right away, but if done continually, will cause the affected part’s life span to diminish substantially, resulting in its defective operation, if not its catastrophic failure. Another similar driving habit is applying the brakes while hitting bumps or potholes. I’ve read it in a book somewhere that this is bad on the suspension, particularly the ball joints and the tire rods. Since then, I always make it a point to lift off the brakes when hitting sharp road irregularities.
Hello I have a 01 corolla 3spd automatic
Accidentally I shift from neutal to reverse
At 100mph the tires brake like stepping in the brakes
For lest then a second then I shift back neutral and then drive
Nothing happens to the tranny.
My next door neighbors do this all the time to their cars, and yet they wonder why their cars break down on them all of the time, which then forces them to get another (used) one.
Good explanation, a visual would help though.
As another poster here put in another away, doing so will wear out the bands in your transmission over time and will most likely partially or catastrophically fail at some point. Just as an example of what could happen if you continue to do this….a neighbor of mine once had a five year old Pontiac Bonneville that he used as a beater, a vehicle in itself that he never washed or took care of. Each time he pulled out of the driveway, he’d always shift from reverse to drive when the car was still in motion, and would sometimes even end up slamming it into gear. Over the course of about a year and a half to two years, he said the car started to shake on the highway a little bit. Not long after that, he ended up losing the reverse gear, and then the drive gear a few weeks later. He later sold it in “as is” condition and the person who bought it, who just so happened to be a Pontiac enthusiast, ended up detailing it from the outside in, fixed a longstanding gas and oil leak, and rebuilt the transmission from the ground up. Last I heard, it is still running well. Moral of the story here….if you want to blow out your transmission, keep doing what you’re doing. If not, at least try to come to a stop before shifting.
As another poster here put in another away, doing so will wear out the bands in your transmission over time and will most likely partially or catastrophically fail at some point. Just as an example of what could happen if you continue to do this….a neighbor of mine once had a five year old Pontiac Bonneville that he used as a beater, a vehicle in itself that he never washed or took care of. Each time he pulled out of the driveway, he’d always shift from reverse to drive when the car was still in motion, and would sometimes even end up slamming it into gear. Over the course of about a year and a half to two years, he said the car started to shake on the highway a little bit. Not long after that, he ended up losing the reverse gear, and then the drive gear a few weeks later. He later sold it in “as is” condition and the person who bought it, who just so happened to be a Pontiac enthusiast, ended up detailing it from the outside in, fixed a longstanding gas and oil leak, and rebuilt the transmission from the ground up. Last I heard, it is still running well. Moral of the story here….if you want to blow out your transmission, keep doing what you’re doing. If not, at least try to come to a stop before shifting from drive to reverse or vice versa.
as a transmission re-builder for many years, I am appalled at the level of misinformation out there, no only will shifting into drive before coming to a complete stop ruin your automatic transmission, I would have to say it is the single biggest cause of transmission failure, along with towing heavy loads with transmissions not designed for that.
My husband does this and it drives me insane!!!! It may not damage it but it’s still very annoying. Lol
Automatics have things called one way clutches. They are roller sprag type. You can grenade these or simply wear them out. When an automatic is on a hill and it doesn’t roll back when you take your foot off the brake, that is the owc holding. They are all in a timing when shiftng from reverse to drive to stop shafts/planetaries. You damage these everytime you drive your car foward frm rolling backwards in reverse. The transmission needs time to catch up sorta speak.
This does not seem to be purpose of these clutches according to various sources including wikipeida. https://en.wikipedia.org/wiki/Sprag_clutch#Automatic_transmissions
What holds you from rolling backward on a hill with an automatic is the same thing that pushes you forward when you let off the brakes on a flat: the minimally-engaged torque converter is still transferring some of the idling engine’s power to the wheels. Try letting off the brakes in San Francisco and you’ll find there is no one-way-clutch stopping you, and the idle power insufficient. There is such a thing as “hill assist” but I think that’s generally an electronic actuation of the brakes, and usually in manual cars.
In short, it’s not bad to shift from reverse to drive at a slow roll because the transmission doesn’t has a “stopped” point of reference (other than the parking pawl), so speed is all relative to it. Doing so at a higher reverse speed will be a jerky transition for the same reason shifts are firmer at higher RPM (by design).
I must disagree with this article. While one inadvertent shift while still moving will not damage the transmission, doing it day in and day out for about 5 or 6 months will cause transmission failure. Ask me. My husband has wrecked three transmissions so far on three different vehicles. He has driven stick shifts all his life and can’t seem to break the habit of shifting while moving no matter how much I rant and rave. It is a very expensive bad habit.
This article is misleading and I must disagree with this advise. While one inadvertent shift while still moving will not damage the transmission, doing it day in and day out for about 5 or 6 months will cause transmission failure. Ask me. My husband has wrecked three transmissions so far on three different vehicles. He has driven stick shifts all his life and can’t seem to break the habit of shifting while moving no matter how much I rant and rave. It is a very expensive bad habit.
It’s about like slamming a door; Curbing a car; down shifting to slow down; or dry steering. You just don’t do it. Especially in another mans ride. Essentially you saved a fraction of a second by shifting early. What that tells him is that the well being of his car isn’t worth a second of your life. No amount of technical justification will smooth this driving foul over for your friend. This all greatly depends on the car. No one drives my car, but I also drive a lexus. If i had a Kia I would be in the back seat hammered letting a homeless crack head drive with his feet. Because lets be honest, no one respects a Kia.