A question about brakes for any mechanics/car experts.

Discussion in 'Mayberry Lounge' started by odog, Aug 27, 2015.

  1. odog

    odog A cat trapped in a dog's body

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    My elderly mother is taking her car to a mechanic tomorrow. I don't want her to get ripped off (it has happened before) so it would be helpful to understand the problem before she takes it in. She drives a Honda Civic, probably 20 years old (not sure).

    She says that when the car is cold (not driven in a few hours) the brakes work fine. However if she is driving to various places and thus turning the car on and off the brakes start to work poorly. It gets worse the more times that it is started.

    I don't know shit about cars. Is it possible that the brakes are getting too much fluid or something due to the car being turned off and on many times? I'm clueless here. Any help is appreciated.
     
  2. ToxicShocker

    ToxicShocker Black Belt

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    Flush and replace all brake fluid and test again. As the brake system and engine bay heat up the fluid used to compress the brakes does not withstand as much pressure. When the same fluid is ancient it will absorb moisture and air and be even weaker under pressure.

    Have them service the flux capacitor too in case no one ever did it before.
     
  3. odog

    odog A cat trapped in a dog's body

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    Thanks.


    And I'll make sure they check the flux capacitor. Lol.
     
  4. ToxicShocker

    ToxicShocker Black Belt

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    At the age of that car it could also be a leak, probably the master cylinder needing to be rebuilt. But the fact that it doesn't happen when it's cold is an indication that its not a leak alone.
     
  5. Jermei

    Jermei Steel Belt Platinum Member

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    Master Cylinder. Check her brake fluid level and make sure she's not driving without fluid or she'll die. Check the master cylider for leakage too. Check the brake lines for leakage. Ive replace a master cylinder on a civic myself. Its all online if you decide to diy.
     
  6. MoparOrNoCar

    MoparOrNoCar Black Belt

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    Check the master cylinder under the hood. Anyone can do it. Just google 1995 Honda Civic Master Cylinder and find it under the hood. Open the cap and make sure the fluid is at it's recommended level. If you want to get into it, check the fluid when it's cold and then check the fluid when it's hot and see if there's a difference. Can also sort of check fluid level by driving around and when the brakes feel weak, pump the pedal a few times. Does the pedal get stiffer and braking power return? If so, you're fluid is low or you have misadjusted/worn brakes.

    [​IMG]

    In simple terms, think of the master cylinder as a syringe. When you press the brake pedal, it's like pressing a syringe in, which in turn shoots the fluid out of the MC, through the brake lines and to the front and rear brakes. There should be no air present anywhere in the system from the top of the brake fluid level in the MC, all the way to the wheels. If there is, that's extra pedal travel that needs to be used and it can also cause the brakes to feel weak since the fluid isn't getting to the wheels with the psi required.

    Discs have a caliper, which is that thing hanging on the circle, and the rotor...which is the circle. When the brakes are applied and fluid enters the caliper, there is a piston inside of that caliper which basically presses the brake pad onto the rotor, therefore slowing the car down. Lets say for shits and giggles that the brake pad is 1/2" thick to begin with and it wears down to 1/4" over time. That's a 1/4" of extra travel that the pad has to go to contact the rotor. That extra travel requires more fluid to be shot through that line and into the caliper. If all the brakes are wearing fairly evenly, that's a lot of extra fluid that has to be used now compared to when the brakes were first put on. Drum brakes are the same in theory, they just work differently. The fluid gets shot into what's called a wheel cylinder inside the drum. The wheel cylinder has two pistons that press the two shoes (pads) outward into the spinning drum and slow it down. The same theory applies. The shoes wear down, that's extra travel needed to contact the drums. Extra fluid used. Extra fluid being used means more brake pedal travel.

    I'm no 20 year old Honda expert but the car turning on and off should have zero effect on the brakes. The brakes are a separate entity from the engine and electrical system aside from the brake booster (power brakes). The booster is what makes the pedal easier to press down and is ran off of engine vacuum. All engines require a certain amount of vacuum to run. A vacuum line is ported off the engine and to the brake booster and it's that vacuum action that assists you in pressing the brakes. I'm just a shitty shadetree mechanic but it could be possible that a small vacuum leak develops when the car gets hot and she's feeling that lack of assist in the brake system. Metal and rubber expand when they're hot and it's possible that the vacuum leak appears in that scenario. Then again the car would run differently (mostly just sitting there at idle) depending on the severity of the vacuum leak. The fluid level and pad wear will be the culprit 98/100.
     
  7. odog

    odog A cat trapped in a dog's body

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    Thanks, that helps. I will try to have a look before she takes it to a shop.
     

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