R to D? Stop 1st or no?
April 15, 2010 7:03 AM   Subscribe

Heres the situation…you are backing up in a automatic transmission car down a driveway. It comes time to put it in drive, is there any damage to put it in D before coming to a complete stop?

My wife and I disagree on this. She says it would strip things if you don't. I argue that there are clutches that prevent damage. What say you hive mind?
posted by ShawnString to Travel & Transportation (7 answers total) 4 users marked this as a favorite
Best answer: Anecdotal, but many years ago while I still lived with my father, he would scold those who did not come to a complete stop before shifting from reverse to drive. He said it could damage the car.

Some of the users over at car talk seem to agree with me, including user transman, who seems to know a lot about transmissions.
posted by King Bee at 7:08 AM on April 15, 2010

Best answer: In an old style (pressure driven torque converter) auto transmission, there is almost zero chance of doing any damage to the trans unless you are doing a decent rate of speed. Below about 5mph there is no way at all that you will damage the transmission. None. You may, however, put some shock loading into some of the drivetrain elements, but again you'd have to be doing a decent speed to stand more than an outside chance of doing so.

I have used the switch from reverse to drive as a means of stopping and changing direction during parking manoeuvres for most of the time I have been driving automatics. I used to use it as a means of stopping my old Ford Granada from around 25mph by sticking it straight into reverse and spinning the wheels backwards in a terribly (to me and my student friends) amusing cloud of tyre smoke and noise. This, plus lots of handbrake turns and general hideous abuse, caused an eventual snapping of one driveshaft and several deaths of propshaft rubber joints. But there was no damage at all to the transmission.

You don't need to stop, no. The faster you do the transition, the more chance of doing damage. However, it is extremely unlikely that you will do damage to the gearbox.

In a more modern auto, I have also switched straight from reverse to drive while rolling and it is a fair bit clunkier. There are clutches that prevent damage, but with the more modern auto's that use a proper clutch and are basically just manual gearboxes with a semi automatic shift there is a chance that you'll bust something. Next time I have a rental car, I'll do some investigation and see. A good rule of thumb is that if it goes in with a bit of a bang, it's likely you can damage something if the bang is any bigger. With a more modern (especially front wheel drive) car I'd shy away from doing this kind of thing as the more modern gearboxes are much more fragile than the massively over-engineered ones of ye olden days. But rolling at below walking speed and shifting is almost certainly fine.
posted by Brockles at 7:37 AM on April 15, 2010 [1 favorite]

Dual-clutch automatics are still pretty rare. You'll know if you have one -- they're typically found either as an optional extra, or as standard on more-expensive cars.

I have no basis to back this up, but I also imagine that they've got something built-in to prevent you from deliberately damaging them.
posted by schmod at 7:57 AM on April 15, 2010

While Brockles mentions that it is extremely unlikely that you will damage the gear box (and he knows a thing or two about cars) I subscribe to the philosophies that a) the brakes are there to stop the car and b) transmission repairs are hella expensive. I always err on the side of caution on this one, and I stop before going from reverse to drive.
posted by azpenguin at 9:25 AM on April 15, 2010 [1 favorite]

Response by poster: OK…thanks all, sigh…I guess she is right.

posted by ShawnString at 9:30 AM on April 15, 2010

Going from Drive or Reverse into Park is what will cause problems and grinding as the parking pawl engages and encounters the significant forward speed of the vehicle.
Going from Drive to Reverse before coming to a complete stop is not really harmful. If you're maintaining lots of speed while you're doing it, you'll beat up the transmission and engine mounts since they'll absorb much of the shock. But, if you're parking or maneuvering your car at speeds under 5mph, there's nothing to worry about. That's why Neutral is in between D and R.
posted by Jon-o at 5:56 PM on April 15, 2010

Going from Drive or Reverse into Park is what will cause problems and grinding as the parking pawl engages and encounters the significant forward speed of the vehicle.

Er, yeah. Totally. THis is absolutely true. Just as a (obviously hypothetical, of course) potential example, should your handbrake fail on a, say, Ford Granada and prevent your usual childish shenanigans with handbrake turns as part of your daily shortcut routine to get to college without going the long way around the one way system, and you then try and perform a (theoretically similar) 'park-turn' by slamming the car into park at around 30mph, you won't get the expected and desired instant rear tyre lock up you were after, you will however get this:

Rapid deceleration initially, accompanied by a loud and rapid "TA-TA-TA-TA-TA-TA-TACK!!!......" and the car will then just carry on rolling unhindered.

Park will no longer do anything at all and will just be another neutral from that day onwards. No other internal damage was apparent in the (admittedly short) subsequent life of the car, incidentally.

When you have no handbrake anyway, this is an issue. I had to fix it, then. Erm, hypothetically. So, in summary "Going into 'P' when moving is BAD".
posted by Brockles at 7:41 AM on April 16, 2010

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