Brake bleeding question

[tdr1919]

I just replaced the power booster and a new master cylinder. (month old rotors & pads on the front). Original problem last week was the brake petal went hard and the car was hard to stop. When I pulled the booster I noticed the master cylinder was leaking through the rear seal.
I bled the master cylnder and the pedal is up and hard, but when I start the car the pedal drops down (far enough that the brake lights light up)
Is this because the brakes need to be bled?
When shut off the car the pedal comes back up.
Thanks,
Tom

 

[c4cruiser]

Did you bleed the rest of the system? Chances are that when you removed the M/C from the car, air got into the lines so now when you depress the brake pedal, the air is compressing and not moving the fluid.

Bench bleeding is required on a new master cylinder so you got that part done. Bleed the brakes and you should be good to go (or stop).

 

[tdr1919]

Thanks C4,
My real concern is the pedal dropping down after I start the car, It has been a long time since I worked on a brake system with a power booster.
Tom

 

[c4cruiser]

If you have your foot on the brake pedal before you start the engine, the pedal dropping once vacuum is introduced into the booster (after engine start) is normal. The drop is usually about an inch but feels more like three or more inches.

 

[tyrel]

If the m/c is leaking, I strongly advise you to get a new one. And as c4cruiser said, you need to bleed the brake lines. The symptoms you describe are exactly what happens when you don't bleed.

 

[tdr1919]

If the m/c is leaking, I strongly advise you to get a new one. And as c4cruiser said, you need to bleed the brake lines. The symptoms you describe are exactly what happens when you don't bleed.

Yes, I found the m/c leaking when I removed it to pull the booster,
I replaced both the m/c & the power booster.

Thanks,
Tom