[bairen]

I'm used to having a tangible parking/e-brake (e.g., a handbrake, or one you push in with your foot)... does the brake switch (the button in front of the gear change lever) act as an emergency brake as well?

[TigerFan]

Originally Posted by bairen

I'm used to having a tangible parking/e-brake (e.g., a handbrake, or one you push in with your foot)... does the brake switch (the button in front of the gear change lever) act as an emergency brake as well?

According to the owner's manual:

"Use while driving:
Pull the switch and hold it. The vehicle brakes
hard while the button is being pulled."

AND:
"If the vehicle is braked to a speed of approx.
2 mph/3 km/h, the parking brake
remains set."

Hope this helps

[nonagon]

Originally Posted by TigerFan

According to the owner's manual:

"Use while driving:
Pull the switch and hold it. The vehicle brakes
hard while the button is being pulled."

AND:
"If the vehicle is braked to a speed of approx.
2 mph/3 km/h, the parking brake
remains set."

Hope this helps

The manual says "pull" the button? Shouldn't it be "push?" That's a terrible translation.

[richardew]

You pull it to use or set it and push it to release it, I think. Could be the other way around. It does both, push and pull.

[TigerFan]

Originally Posted by nonagon

The manual says "pull" the button? Shouldn't it be "push?" That's a terrible translation.

You pull the button up to activate the parking brake, or the emergency brake if driving.

You push the button down, while depressing the brake with your foot, to deactivate the parking brake.

This is covered nicely in a video at bmwusa.com:
http://www.bmwusa.com/Standard/Conte...A2aqh9xqo+gXQ=

Videos are the same for 28i and 35i.

[bairen]

quite helpful guys, i'll try to read the manual in more detail, and try to apply 'push' vs 'pull' common sense as needed.

[Lotus7]

To activate the emergency brake you must put your finger under the brake switch and pull upwards. If the vehicle is stopped, the brake will activate and stay on. If the vehicle is moving more than 3kph, the brake will only activate while the brake switch is pulled up. This allows the brakes to be modulated as needed.

Pushing down releases the parking brake if the vehicle is stopped. When moving "pushing" does nothing. Think in terms of the movement of a standard hand activated parking brake lever (pull to activate, push down to release) It's not like a foot brake.

The brakes activate at about 60% of maximum deceleration, so be prepared for a fairly abrupt stop. Haven't tried it on wet or ice covered surfaces, but would expect rapid ABS activation under those conditions.

[Nahoa]

Lotus, do you know that ABS stays in the loop when using the parking break manually? That would be handy to consider in advance of using.

If you don't have some info to support that answer, I volunteer yo to test it out for us from a good 70mph or so . . .

Back to serious, do you know if it activates all four wheels or just the rear?

[Lotus7]

Originally Posted by Nahoa

Lotus, do you know that ABS stays in the loop when using the parking break manually? That would be handy to consider in advance of using.

If you don't have some info to support that answer, I volunteer yo to test it out for us from a good 70mph or so . . .

Back to serious, do you know if it activates all four wheels or just the rear?

Thanks much for the very good questions.

I had naively, and incorrectly assumed that the E-brake operated by using an electric motor to pressurize the front and rear hydraulic circuits. I suspect this was due to wishful thinking on my part. I’ve never seen anything in print and BMW is pretty silent on the details of how their safety systems actually function. I only tried the E-brake once at about 15 mph and the car “nosed-down” as if all (4) brakes were applied.

With your prompting I decided to actually take a look at the real brake system on the car:

With one side of the car jacked at both the front and rear so both wheels on that side were elevated I found that the E-brake functions on the rear wheels ONLY and that it’s actually mechanically operated. With both the E-brake on and the transmission in “Park”, the front wheel spins with no resistance at all. Apparently, the transfer case clutch disengages in “Park”, so the whole front end just freewheels. The rear calipers are made in such a way that the brake pads can be actuated by (3) separate means:

1. By the normal, dual-circuit, hydraulic system used for all normal braking.

2. By a high-speed electromechanical actuator for fast brake application as part of the stability and traction control. If a wheel begins to spin the BMW “EMF” system brakes that side, thereby transferring power to the other side of the vehicle.

3. By a cable that operates a cam actuator at the back of the hydraulic cylinder operating directly on the caliper piston. The (2) mechanical cables are connected to a small servomotor that is, in turn controlled by the E-brake switch. This system is totally independent of the hydraulic and the stability control/traction control systems. The independence means it’s probably extremely reliable and “fail-safe” which one would want for a parking/emergency brake, but it also is not controlled in any way by the hydraulic ABS modulator, so NO ABS when the E-brake is triggered on snow, ice or damp roads. It as analogous as possible to just pulling up a long mechanical hand brake lever, and will probably totally lock the rear wheels on a slick road.

It also makes “Hand brake” ‘U” turns possible in a X3.

[tank531]

I guess the only real world difference to a mechanical lever brake is you get 'no feel' as to how hard you have applied the parking brake - it is effectively on or off. For those of you who live in SF I would need some confidence before leaving on a steep incline as the button gives no feedback!!

[Lotus7]

Originally Posted by tank531

I guess the only real world difference to a mechanical lever brake is you get 'no feel' as to how hard you have applied the parking brake - it is effectively on or off. For those of you who live in SF I would need some confidence before leaving on a steep incline as the button gives no feedback!!

Clearly, that is the biggest drawback of the system - no feel, and no way to adjust the degree of braking except to "cycle' the switch on and off. Also, there is a small, but quite noticeable delay, both on and off, due to the time necessary for the motor to tension the brake cables. I'd estimate it at between 0.3 and 0.5 seconds once the switch is actuated to fully apply the E-brake. That means 30 or 40 (more) feet at 65 mph.

As far as the ability to hold on the hills of SF when parked, I suspect you will have no problems. The E-brake system seems very powerful and really locks the wheels, at least with the relatively new pads and rotors on my 7-month old 35i. Because of the powerful "full" brake application, I'm more concerned with being able to maintain directional control if the E-brake is applied on a slippery surface and locks the rear wheels.

[perto]

From the drivers manual: Set the parking brake firmly when parking;
otherwise, the vehicle could roll. On steep
upward and downward inclines, further secure
the vehicle, for example, by turning the steering
wheel in the direction of the curb.
Could be an idea in SF. What are they mean by firmly, I thought it's was only on or off?

[Razel]

Originally Posted by tank531

I guess the only real world difference to a mechanical lever brake is you get 'no feel' as to how hard you have applied the parking brake - it is effectively on or off. For those of you who live in SF I would need some confidence before leaving on a steep incline as the button gives no feedback!!

I live in Fremont, CA., about 40 minutes from SF. I'm familiar with those streets, but haven't "tested" the parking brake there. However, it holds the car on similar grades here with the engine running and car in drive facing downhill. No movement at all when not touching any controls. Didn't touch the acceleration pedal to see what it would take to move it, though.

Here in Calif. you're supposed to curb the wheels by law when parking on hills.

[Lotus7]

[QUOTE=Razel;10321442
...Here in Calif. you're supposed to curb the wheels by law when parking on hills.[/QUOTE]

Yep, think it's still a $48 fine if the street slopes more than 3% and you forget to curb your front wheels.

Of course that's a lot less than the fines for parking in a no parking or limited parking zone with fines of $63 to $303 and possible towing fees of more than $400 along with the possible thousands of dollars of damage repair to a X3 if it is towed with the rear wheels on the ground. Last year the city of SF raised more than 100 million dollars via parking fines. (2 million citations issued).

[Lotus7]

Originally Posted by perto

...What are they mean by firmly, I thought it's was only on or off?

It is only "ON or OFF".
The manual wording is probably a carryover from the previous wording for cars with handbrake levers.
Lifting the little electrical switch plastic knob "firmly" (as opposed to "weakly") won't put the brakes on any harder, but might make you feel better in a panic situation.

[Harplayr]

Originally Posted by Lotus7

It is only "ON or OFF".
The manual wording is probably a carryover from the previous wording for cars with handbrake levers.
Lifting the little electrical switch plastic knob "firmly" (as opposed to "weakly") won't put the brakes on any harder, but might make you feel better in a panic situation.

I’m waiting for the lawsuit from somebody that sprained their finger by lifting too firmly.
They should put a warning sticker on it with the proper ft.lb. of pressure for activation.

[faston]

This a very interesting discussion. Thanks for all the great info Lotus 7. Do you know if the 'Auto Hold' function (which I love) uses this same mechanical emergency brake?

[Lotus7]

Originally Posted by faston

This a very interesting discussion. Thanks for all the great info Lotus 7. Do you know if the 'Auto Hold' function (which I love) uses this same mechanical emergency brake?

That was a question I also had, but because the engine must be running and the throttle pedal must be pressed to release the auto-hold brake, it was not something that I could test* with the car balanced on two wheels and on two floor jacks.

However, I'm 99% sure that the auto-hold function is accomplished through activation of the electromechanical actuators for the stability/traction control system. My reasons are that the auto-hold activates, and more importantly releases, almost instantly - much, much faster then the E-brakes work, and there is no sound of the E-brake motor running. I'm sure you've heard the E-brake motor when you hit the E-brake switch. It's especially noticeable if you activate or release the E-brake with the engine off.

The only reason I'm not 100% sure, is that this function could also be implemented with a "line-lock" solenoid valve in the hydraulic system as it is on many off-road vehicles.

*(and live to tell about it)

[perto]

Originally Posted by Lotus7

It is only "ON or OFF".
The manual wording is probably a carryover from the previous wording for cars with handbrake levers.
Lifting the little electrical switch plastic knob "firmly" (as opposed to "weakly") won't put the brakes on any harder, but might make you feel better in a panic situation.

I'm not so sure. If you press the brake lever while you pull the knob you feel the brake lever move further downwards. Sins handbrake it's a drum brake independently from the rotor brake why activate the brake pedal movement?

[Lotus7]

Originally Posted by perto

I'm not so sure. If you press the brake lever while you pull the knob you feel the brake lever move further downwards. Sins handbrake it's a drum brake independently from the rotor brake why activate the brake pedal movement?

Sorry, there are NO drum brakes on the X3. Repeat - NO drum brakes: foot operated, hand operated, or operated by any other appendages you can name. Like most modern disk brake equipped vehicles built in the last 15 years in the civilized world, the X3 E-brake (handbrake) works by applying pressure mechanically via a rotary cam to the back of the brake caliper piston. This reduces the hydraulic pressure that needs to be applied by the master cylinder, which is why the brake pedal sinks a little when the E-brake is activated.

The stability/traction control actuator also applies force to the brake pads directly, but via a different mechanism than the E-brake.

[Lotus7]

Originally Posted by Harplayr

I’m waiting for the lawsuit from somebody that sprained their finger by lifting too firmly.
They should put a warning sticker on it with the proper ft.lb. of pressure for activation.

Here you go. Feel free to print, cut and paste on your E-brake switch.

[perto]

Originally Posted by Lotus7

Sorry, there are NO drum brakes on the X3. Repeat - NO drum brakes: foot operated, hand operated, or operated by any other appendages you can name. Like most modern disk brake equipped vehicles built in the last 15 years in the civilized world, the X3 E-brake (handbrake) works by applying pressure mechanically via a rotary cam to the back of the brake caliper piston. This reduces the hydraulic pressure that needs to be applied by the master cylinder, which is why the brake pedal sinks a little when the E-brake is activated.

The stability/traction control actuator also applies force to the brake pads directly, but via a different mechanism than the E-brake.

The E83 has drum brakes on hand brake!!! And it's not 15 year old. OK the world continues to improve.