Confirm my diagnosis

1st Gen

Hmmm
Contributor
:
1991 Protege LX
Since I don't drive the wife's car often it's always a surprise to find out what condition it's in when i do. It's an 06 Mazda 3 hatch with the 2.3 liter engine.
While running an errand I realized the brake peddle was loosing pressure while I sat at a stop light. The car stops fine, but once stopped, the peddle would depress almost clear to the floor. I could release the peddle and push it again as if to reset it and it would have pressure, but it would slowing depress again.

I'm thinking master cylinder.

Thanks.
 
Either that or a leak.
By the way, it is possible to accelerate master cylinder seal wear by using a "depress the brake pedal to the floor" technique when bleeding brake fluid. Doing it this way allows the MC piston to move past the slight (wear) step in the cylinder bore, damaging the piston seal in the process.

It is always better to either pressurize the fluid in the MC reservoir, pull (by vacuum), or gravity bleed the brake fluid.
 
... It is always better to either pressurize the fluid in the MC reservoir, pull (by vacuum), or gravity bleed the brake fluid.
Or just gently stroke the pedal with your hand, rather than jamming it down with your foot like the car is about to drive over a cliff. The purpose is only to flush fluid through with minimal pressure.
 
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Or just gently stroke the pedal with your hand, rather than jamming it down with your foot like the car is about to drive over a cliff. The purpose is only to flush fluid through with minimal pressure.

Yes, as long as you do not push the pedal all the way to the floor. Placing a block of wood under the pedal to limit its travel will prevent the aforementioned seal damage.
 
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