I was wondering if it'll damage our gearbox if we change gears between N and D while car is moving. For example, if we're going downhill, sometimes I'd shift from D to N and let the car roll. When approaching an uphill again, I'd then shift it back to D and press the throttle. I've read somewhere that it doesn't but just wanted to confirm my understanding. I know that shifting from R to D and vice versa while car is not completely still will damage the gearbox.

shift the gear to N when downhill is risky as u will not hv the engine breaking during emergency.

If you engage D from N, especially with your foot on the accelerator, you will shock your transmission. May have impact on lifespan (kill torque converter).

better don't lah bro - dangerous to do that .... maybe unless its full stop already or something ...

I used to do that when I am driving my manual car, but have not tried it before whenever I am driving an auto transmitted car, as I felt it is too dangerous and risking my gearbox and engine durability too. But it is just my personal perception, can anyone with the technical knowledge enlighten us on this? Thanks in advance.

If the objective is to save petrol, no matter how small the savings is, then you are actually hurting your chances by putting to "N" to coast downhill.

When the ecu registers engine drag, ie, some outside force is turning the engine, eg, rolling downhill while having the gears engaged, then it literally shuts off the injectors (0% duty cycle) and therefore, you are using ZERO petrol.

If, however, you disengage the gears, your car merely becomes deadweight, and you need to slow down using the brakes (wear and tear?) but worse, since the engine no longer has anything turning it, it turns itself, using the idle settings + a small amount to ensure sufficient vacuum is generated in the brake booster. This, obviously uses petrol.

Please, just leave it in "D" and drive normally.

I went to Genting last couple of weeks before.. When going down the hill, i try to use N.. i notice the brake is some how "not working".. its like the brake pump is not working or something(the feeling is like trying to brake going downhill when ur engine is off).. i have to press harder on the brake to make the car stop and sometimes i cannot stop the car completely(when slowing down the car for all the "bonggol").. but when i put the gear back on D, the brake works perfectly fine like before.. maybe the the ECU also control the brake pump according to the gears we're using?

I beleive its to do with how much vacuum your engine is generating to assist the brake booster.

Put it this way... When the engine is doing 3-4k rpm, throttle off... the pistons are sucking way harder than at idle. Therefore, you have more vacuum in the brake booster, increasing the assistance.

Thats why you should never ever coast in neutral. Unless you are already at a very slow speed. Even then its not recommended.

Please, just drive to a stop, then only disengage the gears. For auto cars, there really isnt any excuse for this.

I agree with the Bros above, not to let your car roll in N.
it wont save up much fuel but it'll put your life in risk, not to mention your AT.

Never do that.....Safety 1st.