[sudev]

Auto tranny's will also downshift as long as engine is powering the hydraulics needed. However coming to a complete halt has to be done with hand brake. Carefully.

[Tejas Ingle]

Never switch off the engine in auto transmission. If you do this, you will lose engine braking and you will lose clutch (torque convertor).

You can easily down shift in luxury automatic transmission cars. Once the car is very very slow, you can engage parking. This may damage the parking gear, but the car will stop. You cannot engage parking at high speed as it is designed in such a way that it gets engaged only below a certain speed. So now, even if you engage parking when the car is in motion, it is possible that the car wont stop. You will have to wait till the speed drops to enable the parking gear to engage after which it will stop with a jerk.

Now in entry level auto transmission cars there is an option L (low gears) or 1 & 2. If you engage these, you can still get engine braking. If you dont have these options, engage in reverse.

If you are caught in life threatening situation without brakes, feel free to engage reverse gear. This applies to both manual & auto transmission. In manual, it will require some force to engage. Once engaged, rev hard (hard enough to prevent the engine from stalling) and release the clutch. In auto, engage R and rev. This will screw your transmission but save your life...

[Thad E Ginathom]

Auto gear boxes...

They will only obey the downshift instruction if they think it is sensible. Putting the lever on "1" will not engage 1st gear at high speeds. On the other hand, a manual gear box might also not allow slotting into low gears at high speeds, or the result may be stripping of cog teeth only.

Engaging "P" --- stuff will break. The bits might, or might not, jam your transmission and stop your car.

Engaging "R" --- Again, stuff will break. I knew someone who did this, accidentally, at high speed. All that happened was a horrible noise and a big repair bill. It did not stop his car. In fact,he continued to drive it for a few days, but forwards only!

[noopster]

Most autoboxes these days (C segment and above) have manual override (either tiptronic or paddle shifts). Car behaves similar to one with MT and you can follow the same procedure as that for a manual, only it will not judder to a halt in 1.

To bring to a complete stop, I would suggest using the handbrake as suggested by @sudev since you may break the parking pawl if you try to jam it into Park. I once engaged P without coming to a complete halt and didn't like the sound it started to make: luckily I jammed the brake hard before any major damage happened!

[Tejas Ingle]

Originally Posted by Thad E Ginathom

They will only obey the downshift instruction if they think it is sensible. Putting the lever on "1" will not engage 1st gear at high speeds. On the other hand, a manual gear box might also not allow slotting into low gears at high speeds, or the result may be stripping of cog teeth only.

Yup, AT will not shift directly to 1st. it will select lowest possible gear. Thus reducing speed by engine braking. Downshift will be done step by step. Engine braking on AT will take longer than on MT. In MT also, downshift must be done step by step (5-3-1 should work).

Originally Posted by Thad E Ginathom

Engaging "P" --- stuff will break. The bits might, or might not, jam your transmission and stop your car.

If lever is shifted to P, the parking paul wont mesh as I mentioned earlier. It will jus make a sound. It will mesh only after the speed drops below a certain speed. It may damage the parking gear but will definitely stop the car.

Originally Posted by Thad E Ginathom

Engaging "R" --- Again, stuff will break. I knew someone who did this, accidentally, at high speed. All that happened was a horrible noise and a big repair bill. It did not stop his car. In fact,he continued to drive it for a few days, but forwards only!

If you put it in R, definitely the repair bill will be huge, but when your life is at stake, its worth taking that chance. I have seen a demo video where the stunt driver set the car rolling towards a ditch on a steep slope. Then reversed it without using brakes. It worked.

Originally Posted by noopster

Car behaves similar to one with MT and you can follow the same procedure as that for a manual, only it will not judder to a halt in 1.

To bring to a complete stop, I would suggest using the handbrake as suggested by @sudev since you may break the parking pawl if you try to jam it into Park.

I agree with that. Down shifting, evasive manoeuvres and using the hand brake are the best options. But if you are in a critical situation, you should know all your options and dont care about breaking things.Things can be repaired/replaced. Broken bones cause lifetime of pain.

[xander]

Excellent thread Sudev. Luckily I have not experienced a brake failure till now. Is it true that turning off the ignition(or even engine stalling) will cut off power assisted brakes?

Originally Posted by sudev

@TI : You are letting the cat out of bag. In the triology about Emergency Driving that wil get covered under the next thread.

What's the next thread about? Driving without fuel would be a topic much appreciated by all

[sudev]

@xander : Power assist brakes do not get cut off but get extremely heavy

[amitku]

I had an experience of driving back from Jaipur to Delhi at night in heavy rain. Was in a Taxi Indica which had lost the alternator and the brakes (as diagnosed later, the Oil seal of the Brake pump leaked and spilled oil onto the alternator which burnt out).
As the Cab driver could not drive, I took the wheels and managed with gear shifts and with a lot of pumping and hand brakes.
The situation got worse as the battery started to drain out, so I turned off all lights, and pulled the headlight stalk (I considered this would cut off the tail lamp, head light parking lamp and the number plate lamps and also the lights in the instrument cluster).
I then followed a few cars/buses at a safe distance to avoided using the headlight.
Was scary and maybe foolish but was able to reach Dharuhera, where a relief vehicle was waiting.

[DWind]

I had a brake-failure with an Automatic ('96 Toyota Camry) when I was in US. The car brake's master cylinder failed without any warning. I was driving uphill on a twin carriageway and was trying to cross the road to reach my office, and had to slow down/stop to let a 18 wheeler to pass before crossing. I realized that the pedal had gone soft only then and pumping twice or thrice did not seem to make any mark. Since I was only at crawl speeds all I had to do was aim for the central median climb the grass bank and then pull the parking gear. Looking back I felt I should have pulled the hand brake instead of parking gear, but then I though even that would have failed at that moment.

[Aroy]

On my 2000 Esteem MPFI, the brakes stop working if the engine is switched off!

Anyway I have had a few brake failures in Ambassadors, but not since. Even then I practice engine breaking regularly, and once in while try ZERO brake stops, just to keep honed for emergencies!

In fact engine breaking works much better than brakes on highway (in non emergency situations), especially if you want rapid deceleration. Even at 100+, just taking your foot off the accelerator slows the car quite fast, and if you practice rapid downshifts then all the better in emergencies.

[sudev]

No its not that brakes stop working when you switch off. The vacuum assist stops get boost pressure from intake manifold. At this juncture when you apply brakes you not only need force on brake pedal to overcome cars momentum but also much more additional force to over come the resistance of air in the vacuum chamber of assist!!!

So the brakes become harder - much harder - than normal.

[Aroy]

Originally Posted by sudev

No its not that brakes stop working when you switch off. The vacuum assist stops get boost pressure from intake manifold. At this juncture when you apply brakes you not only need force on brake pedal to overcome cars momentum but also much more additional force to over come the resistance of air in the vacuum chamber of assist!!!

So the brakes become harder - much harder - than normal.

Unfortunately, in my Esteem, the brakes stop working after a few pumps (once the vacuum is finished?). The pedal goes soft and the brakes just do not engage. May be it is a flaw, but I have lived with it for 11 years. I do not switch the engine off if I want the brakes to work.

[sudev]

WOW that's a first one. If that is happening do check the brake circuit for leaks. One do you need to top up brake fluid? Two with car stationary and engine on apply full brakes and hold the pressure. Does the pedal slowly sink down?

I do not think it will but just for peace of mind.

Brakes becoming soft and not engaging when vacuum is finished....hmmmm...any one who can explain this???

[Aroy]

Originally Posted by sudev

WOW that's a first one. If that is happening do check the brake circuit for leaks. One do you need to top up brake fluid? Two with car stationary and engine on apply full brakes and hold the pressure. Does the pedal slowly sink down?

I do not think it will but just for peace of mind.

Brakes becoming soft and not engaging when vacuum is finished....hmmmm...any one who can explain this???

No leaks. The brake oil is there and rarely needs to be topped up. Once the vacuum is used up the brake pedal just sinks, as though there is no brake oil! As I have lived with it for 10+ years, I have stopped thinking about it.

[Thad E Ginathom]

Goodness... you may have become used to it, but it certainly is not right!