[anujatwork]

Hi All, Its a standard practice in all Automatics to press the Brake and then shift from N to D & visa versa, or N to R & visa versa. I want to know whether, Brake is pressed only to prevent the car from creeping forward / reverse or does the Brake engage some sort of a clutch inside to remove load from the transmission box during the shift? Another way to ask the same question is that is it safe for the tranny box to shift from N to D without using Brake if the way ahead is absolutely clear. Similarly, is it safe for the tranny box to be shifted from D to N while coasting (say approaching red light 15-20 meters away). I just bought an Altis Automatic and am driving an AT for the first time. Since you have been driving them for years and are an Engineer too, I thought you might be able to answer me satisfactorily.

[echo77]

Brake does not engage any "clutch" because there is no clutch. You can go from N to D or D to N or N to R without brake.

N to R in some automatics will have a lock button on the gearshift that needs to be pressed (for eg honda city), which is usually to prevent accidental shift to R.

[manim]

Originally Posted by anujatwork

is it safe for the tranny box to shift from N to D without using Brake if the way ahead is absolutely clear. Similarly, is it safe for the tranny box to be shifted from D to N while coasting (say approaching red light 15-20 meters away).

I do these at times, modern AT's are electronically controlled so they should be safe.

[Akshay1234]

Originally Posted by anujatwork

Hi All, Its a standard practice in all Automatics to press the Brake and then shift from N to D & visa versa, or N to R & visa versa. I want to know whether, Brake is pressed only to prevent the car from creeping forward / reverse or does the Brake engage some sort of a clutch inside to remove load from the transmission box during the shift? Another way to ask the same question is that is it safe for the tranny box to shift from N to D without using Brake if the way ahead is absolutely clear. Similarly, is it safe for the tranny box to be shifted from D to N while coasting (say approaching red light 15-20 meters away). I just bought an Altis Automatic and am driving an AT for the first time. Since you have been driving them for years and are an Engineer too, I thought you might be able to answer me satisfactorily.

The brake is like a secondary lock, besides the button on the knob which most cars have. Its to prevent any surprises and sudden jerks. You should press the brakes which shifting from N to D or R, you can try without but there will be a jerk.

If a signal is just ahead then take your foot of the accel and see the revvs drop to almost an idle, it is almost as good as coasting. Incase you have to move ahead and you are coasting in N you will have to come to a near stop to engage D.

Do remember to put it into N at signals longer than 20 seconds.

[anujatwork]

Originally Posted by akshay1234

The brake is like a secondary lock, besides the button on the knob which most cars have. Its to prevent any surprises and sudden jerks. You should press the brakes which shifting from N to D or R, you can try without but there will be a jerk.

Toyota Corolla Altis does not have button on the knob. Instead, it has zig zag slit to move the Stick.

Originally Posted by akshay1234

you can try without but there will be a jerk.

You are right, there is a nudge but I got your point. I only wanted to be sure that there will no damage to hardware inside if I 'shift' without using the brake.

[echo77]

There is no hardware damage to car, even if you were accelerating. My kid once accidentally hit D to N and the car just revved up in neutral. There was no noticeable jerk.

[msaudf]

Originally Posted by akshay1234

Incase you have to move ahead and you are coasting in N you will have to come to a near stop to engage D.

I haven't noticed this scenario in any of the auto transmission cars I've used, if we shift back to D from N when the car is moving forward at a reasonable speed of say 40 or 50 km/h, the transmission simply shifts back to the gear of the appropriate speed (mostly 4th) and moves on.

The auto transmissions I've used are mid 90's Toyota's and Mitsubishi's of the same era, oh and a 93 Mercedes 300D.

The reason i think it was OK to do so is because the shift lever were restricted by some kind of mechanism that only released if the brake pedal was pressed and this restriction mostly comes into play while shifting to R from N, shifting from P to any position and shifting from 2 or L or D2 to D1 and ofcourse shifting to P

I could have been handling those cars wrongly as i have not read the user manuals of the said cars as we bought them second hand and they never came with the said manuals.

[Akshay1234]

Originally Posted by echo77

There is no hardware damage to car, even if you were accelerating. My kid once accidentally hit D to N and the car just revved up in neutral. There was no noticeable jerk.

The jerk is there from N to D or N to R if your foot is not on the brake. That too if your car lets to shift without your foot on the brake.

Originally Posted by msaudf

I haven't noticed this scenario in any of the auto transmission cars I've used, if we shift back to D from N when the car is moving forward at a reasonable speed of say 40 or 50 km/h, the transmission simply shifts back to the gear of the appropriate speed (mostly 4th) and moves on.

The auto transmissions I've used are mid 90's Toyota's and Mitsubishi's of the same era, oh and a 93 Mercedes 300D.

Well yes that does happen, now I am no engineer but from what I understand it does put more stress on the transmission. I would rather not make a habit out of that and only do it if its needed.

[echo77]

Originally Posted by msaudf

I haven't noticed this scenario in any of the auto transmission cars I've used, if we shift back to D from N when the car is moving forward at a reasonable speed of say 40 or 50 km/h, the transmission simply shifts back to the gear of the appropriate speed (mostly 4th) and moves on.

When its a fluid coupling, gear# depends on the speed of the rotating fluid...

[msaudf]

Originally Posted by echo77

When its a fluid coupling, gear# depends on the speed of the rotating fluid...

Thanks echo77, so will CVT's and DSG's or other modern automatics behave differently or get damaged of shifted into D from N while moving at some speed?

[echo77]

Sorry, I don't know the details of CVT or DSG.

[Jeroen]

Originally Posted by akshay1234

The jerk is there from N to D or N to R if your foot is not on the brake. That too if your car lets to shift without your foot on the brake..

Really depends on the car. On my Jaguar XJR I can go from N to D without my foot on the brake without any jerk. It just goes from standstill to slightly creeping in one fluid motion. I assume it's a combination of a lot of torque and a very sublime auto box.

And the XJR drives at quite a steady pace when just idling in D. Unless you engage Sportsmode it will pull away in second gear! Still, no jerks!

Jeroen

[Guna]

Originally Posted by echo77

When its a fluid coupling, gear# depends on the speed of the rotating fluid...

Can you elaborate this point?

[echo77]

IIRC there is something called speed governor and it depends on the rotating speed at the load (output)

http://en.wikipedia.org/wiki/Fluid_coupling

http://en.wikipedia.org/wiki/Torque_convaerter

[Akshay1234]

Originally Posted by Jeroen

Really depends on the car. On my Jaguar XJR I can go from N to D without my foot on the brake without any jerk. It just goes from standstill to slightly creeping in one fluid motion. I assume it's a combination of a lot of torque and a very sublime auto box.

And the XJR drives at quite a steady pace when just idling in D. Unless you engage Sportsmode it will pull away in second gear! Still, no jerks!

Jeroen

Of course there is no hard or fast rule about the jerk, but then again we are talking about a Corolla while your car is a Jyaguar. Again I guess it depends from gearbox to gearbox, but in India I would say its better to keep your foot on D rather than have your car go slightly forward even by mistake considering the cars here are inches apart.