# A car question

#### Pre-AlgebraDude

I was wondering, anyone who know about cars and such, is it hard on your transmission to shift it while you're moving? I do it all the time, but my don't-abuse-transmission-crazy dad yells at me and says it is, but I've seen it done before many times, and they keep right on going. And I mean from like reverse to drive, or drive to low gear.

Oh, and is it possible for your car key to be run through the ignition/door locks so many times and it gets worn out to the point where it doesn't work anymore?

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#### brewnog

Science Advisor
Gold Member
Pre-AlgebraDude said:
I was wondering, anyone who know about cars and such, is it hard on your transmission to shift it while you're moving? I do it all the time, but my don't-abuse-transmission-crazy dad yells at me and says it is, but I've seen it done before many times, and they keep right on going. And I mean from like reverse to drive, or drive to low gear.
How do you mean, to shift it while you're moving? The whole point of a transmission is so you can change gear while you're moving!

You should only shift into reverse while the car is stood still.

You shouldn't shift from a high gear into a very low gear since the road wheels will force the engine speed right up, and possibly over its limit. This is more of an engine concern than a transmission concern though.

Oh, and is it possible for your car key to be run through the ignition/door locks so many times and it gets worn out to the point where it doesn't work anymore?
Possible, yes. I've never heard of it happening though, even on really old, frequently-used cars.

#### Pre-AlgebraDude

brewnog said:
How do you mean, to shift it while you're moving? The whole point of a transmission is so you can change gear while you're moving!

You should only shift into reverse while the car is stood still.

You shouldn't shift from a high gear into a very low gear since the road wheels will force the engine speed right up, and possibly over its limit. This is more of an engine concern than a transmission concern though.

Possible, yes. I've never heard of it happening though, even on really old, frequently-used cars.
I mean in automatics! and I mean going to lower gears for better braking. should you stop first?

#### hypatia

Your father is right, more so if you drive a ford or chevy. I would yell at my kid too if he did that...but he dosen't

note...no, you dont stop for lower gears.....but into reverse..and out of reverse ..YES

#### brewnog

Science Advisor
Gold Member
Pre-AlgebraDude said:
I mean in automatics! and I mean going to lower gears for better braking. should you stop first?
No. That would be silly.

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#### Curious3141

Homework Helper
Pre-AlgebraDude said:
I was wondering, anyone who know about cars and such, is it hard on your transmission to shift it while you're moving? I do it all the time, but my don't-abuse-transmission-crazy dad yells at me and says it is, but I've seen it done before many times, and they keep right on going. And I mean from like reverse to drive, or drive to low gear.

Oh, and is it possible for your car key to be run through the ignition/door locks so many times and it gets worn out to the point where it doesn't work anymore?
I think brewnog misunderstood your question. You're referring to automatic transmissions, aren't you ? It *is* bad for the transmission to go between L, 2,3, D whilst moving. Keep doing it and you'll fry your tranny in little time.

You should only engage the low gears when you need to climb steep hills. In that case, the car should be brought to a complete standstill and you should gently move the lever to L or 2 or whatever. You should keep it in low gear for the downhill descent as well, it will afford you engine braking and prevent overheating of the brakes. When you've crested the hill, slow down to a near standstill before engaging D, then moving off on a flat road.

Manual gearboxes afford a lot more control (of course). They can even be shifted without using the clutch if you know how to match revs (but this is not advisable, since it never comes out perfect unless you're using a special kind of transmission with straight-cut gears, called a crashbox or dogbox).

#### TOKAMAK

first and second gear on an automatic are for "pulling stumps out of the ground".

#### brewnog

Science Advisor
Gold Member
Even with an automatic, I've never heard that there's anything wrong with changing out of D whilst moving. The only difference is that you're making the decision, instead of the gearbox. Modern automatic systems will even override any gear change you make which would force the engine revs dangerously high.

Are we talking crazy big old American cars here, with drum brakes, gas lamps, and hand starters?!

#### Lyuokdea

I don't believe there is anything wrong with going into L or 2 while moving forward, as long as you are going somewhat slowly. I do it quite frequently when I'm driving on ice in fact (basically 6 months out of the year living in Ohio) shifting on ice is a fairly good way to slow the car down without spinning it out on ice.

~Lyuokdea

#### Curious3141

Homework Helper
I stand corrected. There should be no problem when moving from D to L whilst moving, at least at low speeds. And, as brewnog said, even if you screw up, most modern autos are designed to prevent over-reving the engine. Times when you might want to use the lower gear lock would include hazardous conditions, as Lyuokdea pointed out.

What you shouldn't do is to go from D to N or especially D to R whilst moving. Those are bad, no question about it.

I don't have much experience on autos, having driven only manuals all my life. I'll never drive an auto, though I might consider a proper F1 style paddle shifted SMG. :D

#### Pre-AlgebraDude

I know about manual transmissions. Yeah, I'm talking about american cars.

by the way, hypatia, what's wrong with ford and chevy?!

brewnog wrote:
Are we talking crazy big old American cars here, with drum brakes, gas lamps, and hand starters?!

WTF are you talking about, hand starters, gas lamps, and drum brakes? You got something against American cars?!

Our cars start with keys, just like any other cars. Oh wait, I forgot, you gotta-be-fancy-know-it-all Britains gotta have "push button" starters and "push button" transmissions (no offense; I don't like foreign cars, that's all).

TOKAMAK wrote:
first and second gear on an automatic are for "pulling stumps out of the ground".

lol, once I had the truck in 4 wheel low, and first gear, and my dad gets in a and goes "why you got it in tree-climbing gear"?

One more thing, I mean shifting it from reverse to drive while it is barely moving, like you're fixing to put it in drive, but you shift it about a second and a half before it gets stopped, and stupid sluggish transmissions don't shift 'till about a second after you've put it in gear, so you're pretty much stopped by the time the transmission catches up with you.

Curious3141 wrote:
Manual gearboxes afford a lot more control (of course). They can even be shifted without using the clutch if you know how to match revs (but this is not advisable, since it never comes out perfect unless you're using a special kind of transmission with straight-cut gears, called a crashbox or dogbox).

On american cars you'll bust a tooth off the gear doing that.

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#### russ_watters

Mentor
Well, I used to shift from R to D while still moving backwards. Not a good idea. Of course, now I drive stick, so you can do that without any problem.

#### moose

The lower gears on an automatic work great when going down a long slope on a mountain or something if you don't want to wear out your brakes. It's called engine compression breaking I believe. In normal driving conditions, don't do it....

#### hypatia

Both Ford and Chevy car owners manuals use to tell you never to shift into reverse with out being at a compleat stop.

#### Moonbear

Staff Emeritus
Science Advisor
Gold Member
Curious3141 said:
What you shouldn't do is to go from D to N or especially D to R whilst moving. Those are bad, no question about it.
What's wrong with going from D to N? Are you sure you didn't mean D to P? Other than trying to restart the car while still rolling if you stall on a highway, I'm not sure how many other uses there are for Neutral on an automatic (remember, I grew up in NJ, you don't always have the option to brake and pull over before restarting; whether it's good or bad for the engine is irrelevant when the greater threat is the car barrelling toward you from behind).

#### Curious3141

Homework Helper
Moonbear said:
What's wrong with going from D to N? Are you sure you didn't mean D to P? Other than trying to restart the car while still rolling if you stall on a highway, I'm not sure how many other uses there are for Neutral on an automatic (remember, I grew up in NJ, you don't always have the option to brake and pull over before restarting; whether it's good or bad for the engine is irrelevant when the greater threat is the car barrelling toward you from behind).
I meant D to N. There are a lot of drivers who think the "right" thing to do when stopped at a light is to shift the car to N then back to D when moving off. This is wrong.

From the Automobile Association of Singapore website FAQ on auto trannies :

"Q. Does one keep the auto gear engaged while waiting for the traffic light to change to green or shift it to neutral?

A. The gear should remain at D position. Changing gear frequently from D to N and back will cause more wear to the valves and clutch plates.

Q. Is it true that it is not advisable to "free"the gear at N and let the vehicle roll slowly when approaching a traffic light?

A. It is not advisable to shift to N while on the move as this may damage the internal parts of the device. When engaged at N, deceleration will allow the output shaft to overrun the hydraulic clutches and the gear trains of the gearbox. All hydraulic clutches at this gear will be at a disengaged position. The driving and driven plates will be separated slightly as they rub against one another, causing premature wear and tear. At D position, the governor or speeds sensor in the Electronic Control Transmission is still in operation. There will then be an automatic downshift, also known as coast downshift, to give better control of the vehicle and engine braking."

#### Danger

Gold Member
Pre-AlgebraDude said:
On american cars you'll bust a tooth off the gear doing that.
No way. Half of the time driving the Roadrunner or any other 4-gear, I didn't bother with the clutch. The shifts are smoother than with one.
The El Camino has a manual valve body in the 350 Turbo tranny, so I can make positive down-shifts whenever I want to. That's good, because I have to do it to stop. If I use the brakes driving around town, they start squealing within a few blocks. Those 33" tires put a hell of a load on them, even with a light vehicle. Also, my town is located at the bottom of 3 incoming 8% grade hills. First or second gear is the only way to keep from speeding without constantly using the brakes. Trucks are required to use low gears, but using a jake within town limits is illegal. The biggest problem with positive down-shifting is reverse shock loads on the U-joints and engine bearings.
As for the keys, they most definitely will wear out. GM's are the worst because they're so small to start with. If you can pull a GM key out of the ignition without turning it off, it's time to replace it. Since the wafers wear along with the keys, and the keys get thinner as well as stubbier, it's usually a matter of the key breaking before it stops working. Get your duplicates made before the first one wears down, or have it cut to code. A new key cut by tracing from a worn one usually won't work properly.

#### DaveC426913

Gold Member
I drove my Toyota as if it were a stick shift for a while. Mechanics spotted it right away. They said "You're not supposed to drive an automatic like it's a standard." I'd burned out the tranny.

It's not that the actual engine rev causes damage, the tranny of an auto is not meant to withstand the wear & tear like a manual. The friction plates between axle and drive train will burn out.

Your dad's bang on.

#### Moonbear

Staff Emeritus
Science Advisor
Gold Member
Curious3141 said:
I meant D to N. There are a lot of drivers who think the "right" thing to do when stopped at a light is to shift the car to N then back to D when moving off. This is wrong.

From the Automobile Association of Singapore website FAQ on auto trannies :

"Q. Does one keep the auto gear engaged while waiting for the traffic light to change to green or shift it to neutral?

A. The gear should remain at D position. Changing gear frequently from D to N and back will cause more wear to the valves and clutch plates.

Q. Is it true that it is not advisable to "free"the gear at N and let the vehicle roll slowly when approaching a traffic light?

A. It is not advisable to shift to N while on the move as this may damage the internal parts of the device. When engaged at N, deceleration will allow the output shaft to overrun the hydraulic clutches and the gear trains of the gearbox. All hydraulic clutches at this gear will be at a disengaged position. The driving and driven plates will be separated slightly as they rub against one another, causing premature wear and tear. At D position, the governor or speeds sensor in the Electronic Control Transmission is still in operation. There will then be an automatic downshift, also known as coast downshift, to give better control of the vehicle and engine braking."
Oh, okay, I've never heard of anyone doing anything weird like that. Though, that's not a problem for the transmission, but the clutching mechanism. That would rather defeat the purpose of having an automatic if you had to keep shifting when approaching lights. (Needless to say, you don't want to be slamming the car into Park without it being at a full stop first either :surprised).

#### BobG

Science Advisor
Homework Helper
For a standard, it's better to be in Neutral when you're stopped at a stop light. For automatics, you shouldn't interfere with the transmission's operation unless you have a good reason. Going down prolonged steep grades is a good reason to put the car in a lower gear and leave it there (every so ofen, we have a few Pikes Peak tourists that ignore that advice, manage to skip the mandatory brake check at Glenn Cove, and wind up plunging over the side of the mountain to their deaths when their brakes overheat and fail - makes for a chilling tale from witnesses who see the car speeding down the hill, honking it's horn, and flashing it's lights.

Shifting from Reverse to Drive (or vice versa) is bad for both Standards and Automatics. You can probably get away with it at extremely slow speeds, but it's still a bad idea and wears on your transmission. I borrowed a friend's standard that had a small shifting problem. You had to go almost all the way up to Reverse to go from 1st to 2nd or from 2nd to 1st. Going up a hill, I went up just a little too far while going from 2nd to 1st, mistimed the clutch, and dropped his bell housing all over the road, even with the clutch barely disengaged. Fortunately, it had enough other problems that he wasn't too broken up about it.

The 4WD is a completely different matter. You can shift into 4-Wheel high while moving, but I wouldn't do it at extreme speeds (75 is the speed limit on the expressway and that's probably pushing it as an upper limit for shifting into 4WD). To shift into 4-Wheel low, you should be stopped or barely moving - of course, you should be going pretty slow if the conditions require 4-Wheel low, anyway. I don't think you're supposed to drive above 20-25 mph while in 4-Wheel low.

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#### FredGarvin

Science Advisor
Pre-AlgebraDude said:
I mean in automatics! and I mean going to lower gears for better braking. should you stop first?
It is not fatal, but it does make the engine work harder. When I lived in Germany, down south in Bavaria and Austria there are signs in the mountainous areas suggesting to use your engine to help braking on the downward slopes. Your brakes will overheat before your engine does (if it is maintained properly).

Like Brewnog said before, you do have to make sure that your RPMs don't redline when you downshift.

#### Astronuc

Staff Emeritus
Science Advisor
Curious3141 said:
I think brewnog misunderstood your question. You're referring to automatic transmissions, aren't you ? It *is* bad for the transmission to go between L, 2,3, D whilst moving. Keep doing it and you'll fry your tranny in little time.

You should only engage the low gears when you need to climb steep hills. In that case, the car should be brought to a complete standstill and you should gently move the lever to L or 2 or whatever. You should keep it in low gear for the downhill descent as well, it will afford you engine braking and prevent overheating of the brakes. When you've crested the hill, slow down to a near standstill before engaging D, then moving off on a flat road.

Manual gearboxes afford a lot more control (of course). They can even be shifted without using the clutch if you know how to match revs (but this is not advisable, since it never comes out perfect unless you're using a special kind of transmission with straight-cut gears, called a crashbox or dogbox).
I have driven both, and I agree with Curious - shifting an automatic transimission (which I do on occasion) like a manual one is going to increase where and tear, simply because one will increase the load/stress on the components. Use the brakes - brake pads are relatively cheap compared to transmissions.

As for going downhill, use low gears, but one does not have to stop first. One should rev the engine though to get the engine speed compatible with the lower gear. Use the breaks to keep the speed down and minimize stress on the engine/transmission.

Pre-AlgebraDude said:
by the way, hypatia, what's wrong with ford and chevy?!
. Despite what they might say, Quality is not Job #1. Chevy is the lowest (cheapest) end of the GM line. Ford is about the same. Highest quality goes into Cadillac (GM) and Lincoln/Mercury (Ford), but even there, one has to watch it.

#### brewnog

Science Advisor
Gold Member
BobG said:
The 4WD is a completely different matter. You can shift into 4-Wheel high while moving, but I wouldn't do it at extreme speeds (75 is the speed limit on the expressway and that's probably pushing it as an upper limit for shifting into 4WD). To shift into 4-Wheel low, you should be stopped or barely moving - of course, you should be going pretty slow if the conditions require 4-Wheel low, anyway. I don't think you're supposed to drive above 20-25 mph while in 4-Wheel low.

Ha, we used to have an old 4WD. When shifting from 2WD to 4WD high (or low, for that matter), you had to stop, and you usually had to reverse a few metres for the front hubs to engage properly! That was fun...

#### Andy

lol, you guys don't still use metal keys do you?

#### Physics is Phun

kind of hijacking here but since this is a car/transmission thread,
in a standard, is it better to gear down while coming to a stop? this would obviously save a bit of wear on the brakes because the engine is doing some of the breaking, but does doing this not also increase the wear on the engine? plus wouldn't the high revs increase the gas consumption? So what is better, shifting through the gears while stopping, or just putting it in neutral/holding the clutch in ???

thanks

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