Did I ruin my brakes?

December 16, 2004 4:06 AM

AutoFilter: In a moment of terrible mental absence this morning, I drove about half a block in second gear with the hand brake engaged. While the right rear wheel smoked and the brake glowed visibly red, there seem to be no other consequences an hour after the fact. Does this merit a call to the mechanic to check it out if other malfunctions haven't arisen?
posted by Verdant to travel & transportation (19 comments total)

Probably not an urgent visit, if you don't notice a difference in how the car handles. Brake pads get pretty hot as a regular part of how they work.

As I understand it, the real risk when you overheat a cylinder like that is that it's going to warp a bit, and so the pads will start grabbing it unevenly--you would feel a throb or a thumping when you brake if that happened.

That being said, you've almost certainly moved up your next brake check milestone by wearing down the pads, etc. It's probably a good idea to run it by for a brake check-up sometime soon, without necessarily making a big deal of this incident.
posted by LairBob at 4:41 AM on December 16, 2004

does the hand brake use the same hardware as the foot brake?
posted by andrew cooke at 6:23 AM on December 16, 2004

Generally, they do, right? The hand brake on most cars just locks the rear brakes into place--there's not a separate emergency brake mechanism, AFAIK.
posted by LairBob at 6:35 AM on December 16, 2004

ah, yes - it seems the handbrake is just a mechanical (rather than hydraulic) way to force the rear brakes on. for some reason i thought it was separate (i think because i had brakes fail on me once and the handbrake still worked - which makes sense now, knowing it is separate from the hydraulics).
posted by andrew cooke at 6:57 AM on December 16, 2004

Is this the same for automatic cars? Because my hand brake on a mazda protege does pretty much nada. Maybe it's not actually engaging? I've driven with it on for blocks without noticing.
posted by RustyBrooks at 7:12 AM on December 16, 2004

Thanks, LairBob, for the advice, and andrew cooke for the link. So far I can attest that this:

Brakes are actually energy conversion devices, which convert the kinetic energy (momentum) of your vehicle into thermal energy (heat).

is very true from what I saw (and smelled) this morning. I'm moving my brake check-up to January from March.
posted by Verdant at 7:14 AM on December 16, 2004

Many car models with rear discs use a seperate brake system for the e-brake. Often a small drum brake inside the disc.

The only really risk of your situtation is if you got the shoes (drum type) or pads (disc type) hot enough to delaminate. When that happens the friction material can fall off reducing the braking capability at that corner. In extreme, wildly unlikely, cases the friction material can be completely removed causing metal to metal contact which can, again unlikely, cause a wheel lock up. Also you may have glazed the friction material reducing its effectiveness which can be hard to tell on a rear brake.

Most brake places will do free inspections. I'd pull into one in the next couple days and have them take a look however they are unlikely to find anything unless you had something else wrong.
posted by Mitheral at 8:09 AM on December 16, 2004

Because my hand brake on a mazda protege does pretty much nada.

Probably because the mechanical line needs to be retightened, or it's snapped entirely. That's why you're supposed to engage the e-brake every so often, even if you never use it.
posted by Civil_Disobedient at 8:19 AM on December 16, 2004

Don't worry about it. You've worn the pad a litlte more than usual, but if you're not hearing the squealer, it's not time to change it. If you get a pulsing feeling when you use the brakes (especially at 60mph or so), then you probably warped the disc, which is also not a huge deal, but more of a nuisance.

Yes they're usually separate mechanisms. On my car, the e-brake is connected to the brake calipers by a cable, which then mechanically squeezes the caliper. The hydraulic system (from the pedal to the brake cylinder) is not involved at all. Given the amount of heat you generated, it sounds like your brake is still working fine. :)
posted by knave at 10:26 AM on December 16, 2004

Using e-brake on an automatic routinely is a good idea, no? Because it takes dead weight off the transmission? - that is, I remember my driving instructor saying, put the handbrake on before you take your foot off the brake pedal, so the car settles its weight against the e-brake, not the transmission.

Writing this, it seems kind of unlikely it would make any real difference but? Must be why I've always called it the parking brake ....
posted by Rumple at 11:58 AM on December 16, 2004

I'm not exactly sure about how automatics work, but in a stick shift you definitely want to park it in gear. The e-brake may hold the car for some time, but they are really not that great in general. I've heard MANY stories of cars rolling into a ditch where the e-brake was the only parking mechanism used. Parking it in gear uses the compression of the engine to keep the car from rolling, which is a very strong guarantee that it's not going anywhere.
posted by knave at 12:25 PM on December 16, 2004

I drive a stick shift and always use the e-brake and leave it in gear. Naively, it surprises me how the compression of an engine can hold back the dead weight of a car on a hill, which is one reason I use the brake!

- If the parking brake failed would it be better to have your stick shift in 1st gear or 4th gear or reverse, if pointed downhill?

- how does an automatic transmission "clutch" work - and what does "park" in an automatic transmission actually do, mechanically? Why can't you roll start an automatic?

(sorry for the derail if its seen that way)
posted by Rumple at 12:40 PM on December 16, 2004

Rumple, check out howstuffworks.com, they've got all your answers.
posted by spaghetti at 12:49 PM on December 16, 2004

I speak from experience when I say that you really should have it checked out if it got so hot as to be red and smoking. You have probably fried the seals in your wheel cylinder on that wheel. You don't notice a difference right now because the other brakes are taking up the slack, but if they fail or even as they wear you could be in trouble. It will probably run a couple of hundred dollars to repair, but then again, your life does depend on those brakes.
posted by TedW at 1:06 PM on December 16, 2004

I defer to Ted...if he's run into the same situation, and had a very specific outcome like that, it's probably a good idea to have it checked out.
posted by LairBob at 1:47 PM on December 16, 2004

TedW: duly noted. I called my mechanic this evening. They'll take a look at it when I drop by this weekend. Thanks for the advice everyone.
posted by Verdant at 2:27 PM on December 16, 2004

Rumple:
Park in 1st or Reverse, as they have the lowest gear ratio (so the most force is required to move the car). 1st and reverse are typically very close as far as gear ratio. Shouldn't matter which direction you are facing.
posted by knave at 4:20 PM on December 16, 2004

I don't know why (probably stubborness on my part) but I can't ever bring myself to park manuals in gear. I know it's safer, I know it's better on the e-brake, etc. This always bites me in the ass when I start a friend's car and immediately take my foot off the clutch -- WHOOMP. Stall. Argh!
posted by Civil_Disobedient at 9:18 PM on December 16, 2004

I don't park my car in-gear for the simple reason that if one mistakenly starts it in-gear, it's going to leap off an embankment and end up in the neighbour's house...

Hot brake issues:

could have cooked the brake fluid, need to replace

could have cooked the hub bearings

could have destroyed the brake pad

could have warped the rotor

could have destroyed any rubber/plastic parts

could have baked the brake cylinder to seizure

I think it'd be best to get it checked out asap.

posted by five fresh fish at 9:46 AM on December 17, 2004