Shifting Auto Trans While Moving


#1

Can any automatic transmission possibly be harmed by shifting from Neutral to Drive while rolling forward at around 30mph, or from Neutral to Reverse while rolling slowly (less than 5 mph) backward?
I only ask because my new CRV makes a very slight sort of grinding sound when I do the N to D rolling shift, and the backward N to R rolling shift causes it to act as if it just stays in Neutral for several seconds, instead of promptly engaging Reverse. The manual of course says nothing about this. I thought all automatics were just fine with being shifted from Neutral to Drive or Reverse while moving, as long as you were headed in the right direction.


#2

It shouldn’t hurt anything. But I also can’t think of any good reason to do it.


#3

I’ve shifted from N to D while moving more than a few times. Mostly while trying to diagnose a problem. I’ve not shifted into reverse while moving. Most reverse gears are not the strongest in the transmission case, so I tend to be gentle with them. But, I don’t do either as a habit. It would seem to me to put unnecessary stress on parts of the transmission for no real benefit.


#4

Hondas use straight cut gears that tend to be noisy in the transmission. Many Hondas including Civics will make the noise you describe. No harm is done, it’s just in the nature of the car.


#5

I can’t think of any good reason to constantly shift an automatic while moving. If you like shifting…you might want to consider a manual transmission.


#6

missileman –
I can’t think of any good reason to constantly shift an automatic while moving.

Me neither, and I don’t. It’s just something I long ago got into the habit of doing only as I’m leaving my house on a hill. It’s real easy to just roll away from this place, and I mainly started doing it as a way to avoid sticking a car into gear while it’s still fast-idling (mostly a cold weather thing of course).

If you like shifting…you might want to consider a manual transmission.

No thanks. Been there and done that. These modern automatics are good enough that I don’t understand why anyone would want a manual anymore. The Europeans have screws loose as far as I can tell.


#7

Still, it sounds to me like you’re doing what an auto was not intended o do. Just put it in D or a lower gear for engine braking when pulling away from the house going down hill. Please notice that the manual makes no provision for discussing what you are doing. It 's one of those questions that needs no answer as generally, there is no need to do it.


#8

What you’re doing may be illegal in your state, if you care. As others have said, there’s no good reason to be doing this.


#9

One thing about the design of Honda transmissions is that the transition from Reverse to Drive or vice versus involves a dog clutch. When Reverse is selected the dog clutch disengages the 4th counter gear; engages the reverse counter gear; and then engages the 4th/reverse clutch. When going from Reverse to Drive, the 4th/reverse clutch is disengaged; the dog clutch disengages the reverse counter gear; engages the 4th counter gear; and then engages 1st clutch pack.

When you do the transistion on the fly, the counter gears are moving in opposite rotations so the dog clutch has to bump the driven part of the clutch and plates up to the speed of the counter shaft. This could lead to some grinding as the teeth bounce by. I don’t know if the TCM software is aware that the dog clutch is not engaged before applying the 4th/reverse drive clutch. The timing would be most critical going from Neutral to Reverse while rolling as the 4th/ reverse clutch would engage soon after the dog clutch transition is commanded. That might lead to grinding and no motion in Reverse. Going from Reverse thru Neutral to Drive would not be as critical as the dog clutch has all sorts of time to transition before the 4th clutch engages.

Hope this satisfies your curiousity.


#10

Patient-“Doc, it hurts when I do this.”

Doctor-“Stop doing that!”


#11

Thanks, Henny.


#12

Envision pushing your CRV up to 5 mph by hand and then changing its direction by hand. It would take a huge amount of force to stop all that inertial energy and reverse its direction, wouldn’t it? Guess what? Your torques converter has to suddenly accept all of that force, convert it into heat energy, and dissipate it through the tranny cooling system. Ouch!

You know that grinding would is your car’s way of saying “don’t do this”. Follow Henny’s advice (as quoted by Texases) and listen. My philosophy is that of I’m doing something that might hurt the car, I stop doing it.


#13

I always heard you aren’t supposed to shift into reverse unless the car is stopped, regardless of the transmission. I checked and my 2014 Mustang manual states the car should be stopped before putting it in reverse for both manual cars and autos.
As for not understanding why someone would drive a manual when autos are so good nowadays, I think manuals are more fun and make you feel like you are really driving the car. My 2014 Shelby GT500 is only available as a manual. It is exhilarating to downshift into second at 60 and feel the power as the car surges forward. If you can’t understand why people would drive a manual maybe you aren’t imagining driving the right kind of car.