Quick driving question:
I back my car (automatic), out of the driveway. Since I am perpetually late, I do this rapidly. I step on the brake, shift into drive, and toodle on along on my merry way. My question: If I don’t stop all the way in reverse before shifting into drive, will this do bad things to my car? And please be gentle in your explanation, as I know nothing about cars other than the basic idea of how the engine itself works.
I knew a guy who did that whenever I was along. (My boss.) So one day I asked him if this had a deleterious effect on his car. “No,” he replied emphatically. In fact he claime he’s done this with every car he’s had and it never caused a dime’s worth of trouble.
I must admit I have slapped the car into drive prematurely, but only when I was in a white hot hurry.
It’s putting a bit extra stress on the transmission and torque converter. Basically, you are trading wear on brake pads (a $20 part) for wear on the transmission (a $1000 part). Fortunately, the transmission is a fairly beefy part, after all, it is designed to move the entire car, so it’s not like it’s going to wear out in a week of abuse. Some of it depends on how fast you are going in reverse when you plunk it into drive. If you’re not going very fast at all then the stresses aren’t much worse than just a hard acceleration. If you’re going faster though then the stresses are much worse than the transmission would otherwise experience during normal use, and I’d expect it to wear out early.
The effect depends on the particular transmission. While the practice generally won’t do significant harm to a rear-drive American car transmission, it can do major damage to a front-drive Honda transaxle. I would suggest that an extra two seconds to come to a complete stop before shifting is a worthwhile investment.
I had a friend who would occasionally drive his Grand Marquis about 15mph backward and then would quickly throw it into drive (on purpous) to get the wheels really spinning (hey, it’s a ford, all you can do right?).
Well anyway, the most he every broke were a couple of driveshafts. Keep in mind, that is some serious abuse to your tranny! He eventually stopped this practice and never really had any problems with it for many years and then sold it.
So yeah, it’s bad, but not to the extent that you’re doing it.
When I switch to D when the car is backing slowly(no gas applied), then the car will slow down gently untill it stops and then start moving forward.
But if the car is moving backwards with a lot of speed, then when switching to Drive, the tranny will start making a funny clicking noise, but the car won’t slow down. I believe what makes this sound is some mechanism similar to a torque wrench, so that when the maximum power is exceeded, the driveshaft is disengaged from the transmission.
By the way, my car is a Hyundai Santa Fe
In some manual of a former car (don’t ask me which or to provide a cite), it said that shifting into D while still coasting backwards at slow speeds would not harm the car.
It warned against shifting into reverse if there was ANY forward movement.
What about going through neutral? Let’s say you need to back up 10 feet before you can shift into drive. Take the first 7 feet in reverse, then brake gently (not a full stop) while shifting into neutral. After you’ve coasted the last 3 feet, shift into drive and off you go. Is that better or worse than going directly from reverse to drive? I also know very little of the workings of a transmission, so I echo NinjaChick’s request.
Shifting between “drive” and “reverse” before coming to a complete stop is Not Good[sup]TM[/sup].
We had a lot of snow in Ohio last winter. Our 1997 GMC Safari van got stuck in the snow on a couple of occasions. To get it out, I rocked it back and forth by slamming the transmission from drive-to-reverse-to-drive-to-reverse etc. (I’m sure you’ve seen this done before.)
Bad Idea. Bad Idea.
Yea, I eventually got it unstuck. But a month later the transmission self destructed. I am now $2000 poorer. 
In the drive/reverse scenario, the drivetrain has the added stress of inertia and, depending on the speed, weight of the vehicle and traction, the added stress can do major damage to various parts within the drivetrain.
Any part that is stressed in normal conditions will see that stress increased if the drive/reverse technique is used. These parts can include U-joints, driveshafts, CV (constant velocity) joints, axles, ring and pinion gears and, within the transmission itself, planetary ring gears, clutches and steels and the mainshaft that connects all of these parts.
Also noteworthy is the fact that a lot of the parts that can be damaged by this are parts that were never expected to wear out or be replaced (like planetary gear$) so are fairly expensive.
But, I do it too.
You know, I swear people ask this question because they seem to think that there’s something magical about an automatic transmission. Like, if you shifted into R while cruising at highway speeds you wouldn’t just damage your car, you’d rip the fabric of space-time and fall into an alternate universe or something…
In answer to the OP, as long as the car is only barely moving, no, you’re not going to do any extra damage. So just get on with your life! 
Wait, wait. That’s not what happens?
Well, damn, that explains everything.
Someone mentioned doing damage to a Honda front-drive tranny by shifting prematurely. Has anyone noticed that Honda seems to be the only auto tranny that sounds like a manual while backing up, i.e. loud gear whining? Every other automatic I have aver driven sounds exactly the same as going forward in first gear, but the Honda sounds just like a manual. Has anyone else noticed this?
You might consider backing the car into your driveway, then you get moving even faster w/o the worry when you are running late.
Very perceptive. Most automatic trannies use planetary gearsets. The Honda ones are essentially manual transmissions with internal clutch packs (not related to a standard clutch) to shift the gears, and a torque converter instead of a clutch. So it sounds like a manual trans because, in that respect, it is a manual trans.