08-28-2011, 10:50 AM | #1 |
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probably dumb question: does this car have an emergency brake?
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?
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08-28-2011, 10:59 AM | #2 | |
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"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 |
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08-28-2011, 11:05 AM | #3 | |
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The manual says "pull" the button? Shouldn't it be "push?" That's a terrible translation. |
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08-28-2011, 11:09 AM | #4 |
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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.
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08-28-2011, 11:15 AM | #5 | |
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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. |
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08-28-2011, 11:21 AM | #7 |
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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. |
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08-28-2011, 03:24 PM | #8 |
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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?
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08-28-2011, 05:48 PM | #9 | |
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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. |
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08-29-2011, 04:46 AM | #10 |
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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!!
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08-29-2011, 10:12 AM | #11 | |
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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. |
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08-29-2011, 10:28 AM | #12 |
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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? |
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08-29-2011, 04:19 PM | #13 | |
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Here in Calif. you're supposed to curb the wheels by law when parking on hills.
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08-29-2011, 04:41 PM | #14 |
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[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). |
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08-29-2011, 04:50 PM | #15 | |
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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. |
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08-29-2011, 06:47 PM | #16 | |
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They should put a warning sticker on it with the proper ft.lb. of pressure for activation. |
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08-29-2011, 07:14 PM | #17 |
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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?
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08-30-2011, 01:18 AM | #18 | |
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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) Last edited by Lotus7; 08-30-2011 at 01:23 AM.. |
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08-30-2011, 01:43 AM | #19 | |
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08-30-2011, 02:10 AM | #20 | |
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The stability/traction control actuator also applies force to the brake pads directly, but via a different mechanism than the E-brake. Last edited by Lotus7; 08-30-2011 at 02:25 AM.. |
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08-30-2011, 02:15 AM | #21 |
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Here you go. Feel free to print, cut and paste on your E-brake switch.
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08-30-2011, 08:59 AM | #22 | |
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