Shifting into “drive” while moving backward in a car with automatic transmission is bad, isn’t it?
Or not? Or does it depend on something(s) or other(s)?
-Kris
Well, it’s rough on the transmission if it agrees to do it. Some won’t.
I guess I’m not certain my car agrees to do it or not. You can put the shifter in “drive” position while the car is moving backwards, but maybe it’s not actually shifting til the car has come to a stop?
I don’t know for sure, because this isn’t happening while I’m driving. I always thought this was a big “no-no” so I never do it. My wife, however, does it every single time she changes from reverse to drive. She insists there’s nothing wrong with it.
Our last car would give a violent kick when she did this, but only the first time she did it on any particular day. I insisted she was damaging the car. She insisted it was just happening because the car wasn’t warmed up yet, and she pointed out it jumped a little (though not as much!) even when she first came to a full and complete stop.
So anyway, now we have a new car, and I want to know once and for all whether she’s causing damage when she does this or not. Though it looks like it depends on the car, based on your answer.
-FrL-
While it may not hurt the trans (more on this in a minute) I can state with no fear of contradiction that under no conditions will doing this be helpful to the longevity of the trans.
Note: When used in the next paragraph the word brake refers to a planetary gear brake inside an automatic transmission, not the hydraulic wheel brakes.
On most automatic transmissions moving the shifter moves a valve inside the transmission called the manual valve. Put simply this valve directs fluid to the proper locations for P R N D etc. If the car is moving backward, fluid is being sent to some of the clutches, brakes and freewheels (AKA sprag clutches) inside the trans. Moving the shifter to D 3 2 or 1 will direct fluid to different clutches, brakes and freewheels. If you are still moving backward and you move the shifter the momentum of the car will be driving the innards of the trans one direction, and when D is engaged the engine will be trying to drive the innards of the trans the other. Inside the transmission the a clutch or a brake is going to wind up slipping at least a little bit until the rearward momentum is killed. Slippage causes wear and heat. Wear can cause bits of clutch lining to flake off which can cause problems or if enough material is shed, the clutch or the brake might / will start to slip and then it is trans repair time. Heat is what kills trans fluid, and bad fluid can also lead to transmission failure.
The shock on the driveline can also be very bad for engine / transmission mounts, drive shaft u-joints, CV joints etc.
But what about the may not hurt part? On some electronic transmissions there may be an electronic lockout that prevents the engagement of a gear if the car is moving. For example on the cars I teach on, if you are going over about 3 mph, and try and select reverse, the manual valve will move, but the electronic solenoids are not energized until the speed drops below 3 mph. There is a drive line shock at that speed. Also since the speedo does not know forward from reverse, the electronic prevention is only for reverse. If you are traveling backward, there is nothing to prevent you from selecting D at any speed and hurting things.
My suggestion is stop the car with the brakes, they are designed to do this job, and they are lots cheaper to repair than a transmission. Unless of course you want to be on your AAMCO dealers favorite customer list.
Going by the racket the car makes I’d say it’s not a good idea… (having done so accidently several times)
My HS Auto shop teacher used to pull out this ugly, twisted hunk of metal several times throughout the school year. It was the drive shaft from a late 80s Pontiac Firebird GTA, twisted into pretzel l ike contortions because someone (a former student) was having fun doing “R to D slams” in a parking lot. He’d get the car going about 15 - 20mph in reverse and then slam it into Drive, allowing him to squeal the tires very nicely.
It was a brand new vehicle, and if one of the dealer mechanics hadn’t been witnessing him doing it, he might have gotten it repaired under warranty. As it was, it was not a cheap repair.
So even if it’s not too bad on the transmission, it can be over-stressful on other parts of the car. In fact, the entire driveline. I’d say don’t do it.
What about downshifting to avoid overspeed while coasting down hills in town?
OD to D?
What about OD to 1?
The general rule on downshifting and using engine breaking is that it does put wear on the transmission (both automatic and manual) and clutch, and that wheel brakes, which are much cheaper and easier to replace, should be used instead of downshifting as a general rule.
In cases where not downshifting would cause a potential braking failure, such as in mountain regions, etc, then you do what you need to do to be safe.
In most cars, going from OD to 1 won’t actually shift it all the way down to 1st gear. Most transmissions are electronically controlled and won’t shift down gears until a certain speed threshold is met (probably somewhere around 15mph for 1st gear, but it depends on the car). It will shift it into the lowest gear allowed by the electronic speed controls, so if you’re going 45mph, it might shift into 3rd (or D, or whatever) or 2nd, but almost positively not 1st.
She’s been lucky so far. It’s not true that there’s nothing wrong with it. It is true that it usually doesn’t result in sudden catastrophic failure, but that doesn’t mean that it isn’t shortening the life of the tranny.
Saying there’s nothing wrong with doing this is like saying arsenic won’t hurt you because you’ve eaten it several times and are still alive. Eat arsenic long enough and some morning you’ll wake up dead. Abuse a transmission this way long enough and some morning you’ll wake up to a hefty repair bill.
I don’t see this as much of a problem. all of the parts inside the transmission are traveling the same direction when you downshift. This is way different than going from R to D.
Downshifting is a really good idea on long steep grades, when using just brakes could lead to overheating and fade.
As far as OD to one goes, every auto trans I have ever seen limits as to how fast a lower gear can be selected. For example on one 4 speed auto (Just becasue these numbers stick in my head)
D (OD) to 3 at any speed
3rd to 2 (Or D to 2) @ a max of 74 MPH
2 to 1 @ a max of 33 mph
How about if I’m in town, and coasting to a stop light?
Or cruising down a little tiny hill?
No. In those circumstances, use the brakes. That’s what they’re there for.
I use OD to D all the time in my Ford to go up hills or to downshift and overtake at freeway speeds. Provided I’m not too hard or too light on the throttle, it doesn’t seem to cause too much stress on the drive train.
Or, more generally: If I’m causing excess wear on the car, it’s my driving style in general. 
Time for an anecdote:
My previous Ford had a similar transmission, and I’d use OD->D in order to slow the vehicle without my brake lights illuminating (and thus attracting attention from a highway patrolman). But I stopped doing that one morning when, bleary-eyed and still absorbing coffee, I attempted to shift out of overdrive — and moved the lever the wrong direction, into Reverse.
Drive to Reverse at 80 MPH.
The car indeed slowed, quite rapidly. Even though I realized my error instantly, the tranny had about a half second to engage in reverse before I threw it into neutral. I cautiously engaged Drive again, and pressed the accelerator…
No effect.
So I coasted to a stop and got towed off the freeway by the service patrol. I called my boss and my girlfriend and explained I would be delayed due to car problems, then called the dealership and asked their advice. Then I called AAA for a tow to the garage.
On a whim, I got in the car and started it, and engaged Drive to see what would happen. It moved, and made no horrible noises! In fact, the only noticeable effect was that it took Reverse an extra half second longer to engage than it did before… as if the car was hesitant to comply with that operation again. I took it in for a ATF change and filter inspection to see if there was any debris or small parts in the filter, and found none.
I probably slammed a valve somewhere in the transmission or torque converter, and it just needed to cool down to recover.
Yes, the owner’s manual for one’s particular vehicle will usually have those speeds listed for each of the model’s available transmissions.
IMHO sifting down in those conditions is no different (as far as the trans is concerned) then if you were to press the accelerator to the floor and activate kick down at the same speed. Hell there might even be slightly less wear in the downsift than in a full throttle downshift due to the lack of engine torque being applied.
I don’t see it as being a problem.
Another anecdote: Shortly after getting my first driver license, while backing up I clipped the garage concrete stanchion with my dad’s Chevy Nova. I panicked and slammed the gear lever into Park. The car wasn’t too happy with that and I had to fight the lever a bit to get it out of Park.
Luckily for me, Dad called that “my one free accident repair.” Luckily for dad, it was a cheap repair job for the doors.
I have wondered about this. Perhaps it’s the number of times a downshift at higher RPM’s that add to the wear (and manually downshifting will add to the # of times), also I wondered how much extra wear when one manually downshifts to slow down when you are going to get into that gear anyway.
OK anything you do to the transmission will cause wear. This includes starting the engine, putting it in gear, and stepping on the gas. The question is how much wear, and is that acceptable.
So how much additional wear is created when you downshift? IMHO not much. Since I know of no studies that have looked at this, all I can go by is my years of experience in the car business, and gut feeling.
My experience and gut tell me that downshifting the car every now and agin is not going to knock off a measureable amount miles off the life of the trans. In all my years of auto repair, I have never seen a trans failure that I could even remotly pin to the trans being downshifted. So I downshift if I am going down a hill, or if I am in the mood. If you feel diferent then don’t downshift your automatic.
At at known long stop lights, locked traffic, anything over about 30 seconds, if I am just sitter there, I move the tranny to netural. Makes me all happy and nice feeling and I’ll leave all the reasoning to others…
I’ve downshifted a/t’s for years w/o any problems. You do have to use some common sense and not overspeed the engine and/or tranny. It’s not much different from downshifting a manual, but shifting into a fwd gear while the vehicle is rolling backwards, uh, uh, that’s just not real smart. :smack: