# What causes a car brake pedal to "sink"? **URL:** \ **Category:** Factual Questions\ **Created:** [July 19, 2013, 2:50pm UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937 "2013-07-19T14:50:53Z")\ **Posts on this page:** 10\ **Page:** 3
**Author:** ![Sparky812](https://avatars.discourse-cdn.com/v4/letter/s/eb9ed0/32.png) [@Sparky812](https://boards.straightdope.com/u/Sparky812)\ **Post date:** [July 24, 2013, 11:40am UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/41 "2013-07-24T11:40:51Z")
> [@AaronX](#): > > (Automatic) when in drive, the car would still move forward even with the handbrake applied. Errr… what do you think is going to happen!? The automatic transmission is engaged and is going to fight against your handbrake. Why would you ever (intentionally) put the car in drive with the handbrake applied? Actually, to answer my own question, if you want to disable your daytime running lights while your car is running, you can apply the parking brake slightly. This is particularly useful at the drive-in so as not to have hundreds of people honking at you! ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [July 24, 2013, 1:21pm UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/42 "2013-07-24T13:21:22Z")
> [@AaronX](#): > > (Automatic) when in drive, the car would still move forward even with the handbrake applied. > [@Sparky812](#): > > Errr… what do you think is going to happen!? The automatic transmission is engaged and is going to fight against your handbrake. There are plenty of cars with effective parking brakes that will not move when in gear even if revved up a fair amount. A parking brake that won’t hold against an automatic idling in gear isn’t going to hold against some hills, and is either a poor design or in poor condition. ---
**Author:** ![Sparky812](https://avatars.discourse-cdn.com/v4/letter/s/eb9ed0/32.png) [@Sparky812](https://boards.straightdope.com/u/Sparky812)\ **Post date:** [July 24, 2013, 5:25pm UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/43 "2013-07-24T17:25:18Z")
> [@Gary\_T](#): > > There are plenty of cars with effective parking brakes that will not move when in gear even if revved up a fair amount. A parking brake that won’t hold against an automatic idling in gear isn’t going to hold against some hills, and is either a poor design or in poor condition. I agree. A well-designed, well maintained parking brake should hold at least at an idle, but my point is that by engaging the transmission with the parking brake applied usually causes the damage which results in the “creep” the OP describes. I’m just surprised that the OP doesn’t realize the two opposing forces. ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [July 24, 2013, 6:26pm UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/44 "2013-07-24T18:26:36Z")
> [@Sparky812](#): > > Actually, to answer my own question, if you want to disable your daytime running lights while your car is running, you can apply the parking brake slightly. This is particularly useful at the drive-in so as not to have hundreds of people honking at you! Alas, that disappeared between 2003 and 2008 with two of my GM cars. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [July 25, 2013, 5:22am UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/45 "2013-07-25T05:22:59Z")
Of course I know there are 2 forces. I expect a handbrake to be stronger, that’s all. You’re not supposed to use the handbrake when in gear? ---
**Author:** ![Sparky812](https://avatars.discourse-cdn.com/v4/letter/s/eb9ed0/32.png) [@Sparky812](https://boards.straightdope.com/u/Sparky812)\ **Post date:** [July 25, 2013, 12:00pm UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/46 "2013-07-25T12:00:57Z")
> [@Kenm](#): > > Alas, that disappeared between 2003 and 2008 with two of my GM cars. That sucks, I know it works on my 2003 GMC truck, it worked on my old 1998 Grand Prix not sure about my wife’s 2010 Sienna though. I’ll try it, when I get a chance. I’m in Canada, had(has) different regulations regarding daytime running lights than the USA. Oddly coincidental to the dwindling numbers of drive-in theatres.:dubious: > [@AaronX](#): > > Of course I know there are 2 forces. I expect a handbrake to be stronger, that’s all. You’re not supposed to use the handbrake when in gear? Not usually during regular driving, brakestands, doughnuts, 180s brake turns, etc. notwithstanding. 😃 ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [July 25, 2013, 5:21pm UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/47 "2013-07-25T17:21:02Z")
> [@Sparky812](#): > > I’m in Canada. . . . Me too. I could keep the headlights off on the '03 and '92 with only two clicks of the parking-brake pawl, but not so with the '08. ---
**Author:** ![mandala](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mandala/32/95_2.png) [@mandala](https://boards.straightdope.com/u/mandala)\ **Post date:** [July 26, 2013, 1:51am UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/48 "2013-07-26T01:51:58Z")
I only recently started driving, and I see cars can move even with the hand brakes applied! There is a light in the dashboard that glows, and beeps that alert you, but to me this is completely counter-intuitive. Shouldn’t cars be completely immobile with the hand-brakes applied? Is this a problem with the car itself, or is there some logic to having things work this way? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [July 26, 2013, 4:40am UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/49 "2013-07-26T04:40:21Z")
> [@hniyer](#): > > I only recently started driving, and I see cars can move even with the hand brakes applied! There is a light in the dashboard that glows, and beeps that alert you, but to me this is completely counter-intuitive. Shouldn’t cars be completely immobile with the hand-brakes applied? I wouldn’t say completely immobile, but the parking brake should hold against rolling down a hill, and thus against mild acceleration when in gear. The warning light is meant to be a reminder that the parking brake is set so that the driver will release it before starting to drive. > [@](#): > > Is this a problem with the car itself, or is there some logic to having things work this way? It’s a problem. ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [July 26, 2013, 3:41pm UTC](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937/50 "2013-07-26T15:41:25Z")
> [@hniyer](#): > > I only recently started driving, and I see cars can move even with the hand brakes applied! There is a light in the dashboard that glows, and beeps that alert you, but to me this is completely counter-intuitive. Shouldn’t cars be completely immobile with the hand-brakes applied? > > Is this a problem with the car itself, or is there some logic to having things work this way? Some vehicles have automatic adjusters for the parking brakes and some have to be adjusted by hand. When brake shoes are replaced there are things that need to be addressed with parking brakes that aren’t always done by the back yard miskanic. And if the parking brake hasn’t been a regular part of you driving and one day you decide to engage it, well the brake sometimes will not release fully and that is a big problem! You will be able to smell the hot brake linings but of course that can happen also after a period of hard braking, except the rear wheels brakes will be the hot ones with faulty P-brake release. [Previous page](https://boards.straightdope.com/t/what-causes-a-car-brake-pedal-to-sink/663937.md?page=2)