3 ms·

How can breaks not stop the engine?! Parking break being a different thing, but the main ones?

delinka 11y ago
"Brakes" are at the wheels. The only time stopping a car from rolling also affects the engine is when everything remains engaged (manual transmission, manual clutch; in gear, clutch not depressed to the floor.) In a vehicle with an automatic transmission, the transmission begins to disengage from the wheels as the wheels spin slower than the engine is pushing. (Very simplified explanation...) i.e. brakes on cars are not designed the stop the engine but to absorb the vehicle's momentum.
- radiorental 11y ago
  Also, it's been reported that drivers pumped the brakes in a panic (and understandably so). This will have the effect of reducing the power assist, which is already reduced due to high revs / low vacuum.
  - jmhobbs 11y ago
    I wonder if this is a behavior inherent to older drivers? I'm in my 20's, but my first car was from the late 60's. I hadn't properly bled the master cylinder on my brakes, so I would have to pump them to make them more effective. Just wondering if it's a natural panic behavior, or something learned.
    - drbawb 11y ago
      It's something learned. You are explicitly taught to do it if your vehicle does not have ABS. It prevents the wheels from locking up. ABS does the same thing, and does it much more effectively than a human ever could. Preventing the wheels from locking up under hard braking is crucial to stopping when you have little traction. To provide traction on any surface _wheels must keep rolling._ When wheels are static their contact patch is effectively the size of a hockey puck, that little bit of rubber is not very good at stopping a car going 80MPH. Not compared to disc brakes w/ ceramic pads bleeding off all that energy, at any rate. While I'm on the subject, I'll take this time to drop a PSA: on ice, where ABS is most helpful, the rubber of your all season tires is about the consistency of a hockey puck. -- Please invest in actual winter tires if you get regular snowfall. (Also if you live in Texas: invest in a set of winter tires anyways and go have a blast when the streets are deserted.)
- briHass 11y ago
  I assume the post above yours was referring to the brakes being able to stop a moving car that also has the engine's power being applied, which they easily can do. If the brakes are engaged enough, even a full throttle engine won't be able to keep the car moving.
mikeash 11y ago
By not being used effectively by the driver, mostly. If your car starts accelerating in an unintended fashion, you should push the brakes to the floor and keep them there, then if you have time shift into neutral and turn off the ignition (this shouldn't be necessary, but will help). Many drivers won't actually do this in the heat of the moment, though, thus many deadly crashes.

"Brakes" are at the wheels. The only time stopping a car from rolling also affects the engine is when everything remains engaged (manual transmission, manual clutch; in gear, clutch not depressed to the floor.) In a vehicle with an automatic transmission, the transmission begins to disengage from the wheels as the wheels spin slower than the engine is pushing. (Very simplified explanation...) i.e. brakes on cars are not designed the stop the engine but to absorb the vehicle's momentum.

radiorental 11y ago
Also, it's been reported that drivers pumped the brakes in a panic (and understandably so). This will have the effect of reducing the power assist, which is already reduced due to high revs / low vacuum.
- jmhobbs 11y ago
  I wonder if this is a behavior inherent to older drivers? I'm in my 20's, but my first car was from the late 60's. I hadn't properly bled the master cylinder on my brakes, so I would have to pump them to make them more effective. Just wondering if it's a natural panic behavior, or something learned.
  - drbawb 11y ago
    It's something learned. You are explicitly taught to do it if your vehicle does not have ABS. It prevents the wheels from locking up. ABS does the same thing, and does it much more effectively than a human ever could. Preventing the wheels from locking up under hard braking is crucial to stopping when you have little traction. To provide traction on any surface _wheels must keep rolling._ When wheels are static their contact patch is effectively the size of a hockey puck, that little bit of rubber is not very good at stopping a car going 80MPH. Not compared to disc brakes w/ ceramic pads bleeding off all that energy, at any rate. While I'm on the subject, I'll take this time to drop a PSA: on ice, where ABS is most helpful, the rubber of your all season tires is about the consistency of a hockey puck. -- Please invest in actual winter tires if you get regular snowfall. (Also if you live in Texas: invest in a set of winter tires anyways and go have a blast when the streets are deserted.)
briHass 11y ago
I assume the post above yours was referring to the brakes being able to stop a moving car that also has the engine's power being applied, which they easily can do. If the brakes are engaged enough, even a full throttle engine won't be able to keep the car moving.

mikeash 11y ago

By not being used effectively by the driver, mostly. If your car starts accelerating in an unintended fashion, you should push the brakes to the floor and keep them there, then if you have time shift into neutral and turn off the ignition (this shouldn't be necessary, but will help). Many drivers won't actually do this in the heat of the moment, though, thus many deadly crashes.