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I have a 1991 Honda Civic wagon that loses braking power on hot days. I have it working for the initial press, but as I hold down the brakes I slowly lose braking. I have to repeatedly press at red lights, and after a long day of driving my leg gets tired (ha-ha). Still on a cool day the brakes work without problems. A friend of mine said it might be the brake master cylinder, but I wanted to make sure.

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Have you bleed the brake recently? Did your master cylinder ever been replaced? I had a soft brake line that was bulging when braking and was even worst during summer. –  Gabriel Mongeon Aug 15 '13 at 14:29
    
I've never bled my brake, and never changed the master cylinder. I did change brake line a year ago (left rear side) but this problem has been around long since I've own the car. –  fassetar Aug 15 '13 at 14:35
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You've changed a line without bleeding the brakes, that doesn't sound good. –  Gabriel Mongeon Aug 15 '13 at 14:53
    
You're probably right, but what happened was the line broke and I didn't have a lot of experience working with brakes. So I replaced it and just filled it backup. Worked like it did before, same problems and all. –  fassetar Aug 15 '13 at 15:03
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2 Answers 2

up vote 3 down vote accepted

I had brakes issues with my 1987 Toyota Land Cruiser since 2 years, I've had the same symptoms has you.

Since then I've change all brakes (rear/front), replace some flexible brake hose that were soften due to age and anti-rust treatment with stainless steel hose(might be overkill). Then I bled all four brakes to remove air in the lines which give me a firmer pedal.

Now I have brake but I have to depress my pedal way down to start braking. I know that my master cylinder is faulty because I had bleed it in place and my pedal got less travel to get the same result.

So, to answer your issue:

  • Check any flexible lines to make sure they are in shape: no cracking or bulging under pressure. Replace if necessary.
  • Inspect brake bad and drums, replace if necessary
  • Then bleed the brake, it's cheap (only need new fluid) and fast to do. You should now have firmer brake, if not;
  • You could bleed you master in place to see if it make anything or replace it.

Replacing any component of the braking system you'll need to bleed the system according to the manufacturer specifications.

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Thanks for all the help, I'll be sure to try all that. Lucky for me I bought all the books for my car so this should be easy to start. –  fassetar Aug 15 '13 at 15:25
    
@fassetar, while this is a good answer, and probably a correct one (air in the brake system would indeed cause same symptoms), you should not award the acceptance just because it “looks” right. Try to fix the car first, and if that is indeed what had caused it, then accept. –  theUg Aug 16 '13 at 3:21
    
Check under the brake pedal on the floor for any leaking brake fluid. When the master cylinders fail it usually will start dripping some fluid inside the car there. –  Brian Knoblauch Sep 17 '13 at 18:58
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If after bleeding the brakes and checking the mastercylinder check the replaced brake line. Did you install it in the exact same position as the original? If it passes to close to an exhaust component the heat from the exhaust may be boiling the brakefluid. The boiling fluid would contain a bubble of air that is compressible resulting in low pedal pressure but only while the engine and the exhaust is warm.

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I did install it correctly, but that does add a possibility. I know the left side is fine but the rear right side it could be possible. Sometime when I break the car does slightly pull left more than right. Thanks for the information! –  fassetar Aug 16 '13 at 13:15
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