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I've got another brake question. I'm hopeful someone can help. I've replaced my booster, my MC, and put on new speed bleeders. After bleeding the brakes, I can get good pedal pressure. But, then after I start the car I lose all pedal pressure - the pedal goes to the floor. Can anyone tell me what's going on??

As always, thanks...

 

[taz3]

You could either have air still in the system or it is possible the MC is bad, did you bench bleed the MC first?

 

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Yes, I bench bled the MC. And I got pure fluild from each bleeder, suggesting no air in the lines. What baffles me is that I have good brake pedal pressure until I start the car. When the car starts, I lose the pressure. I hope someone can help.....Thanks,

 

[CARtoon]

The pedal will always be easier to push when the cars running because your booster gets vacuum. Are the wheels locking at all? Have someone step on the brakes and try and turn the wheels. Unlikely but did you forget the mc pin? Also when bench bleeding the mc it's good to knock on it a bit to loosen bubbles that stick inside.

 

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but did you forget the mc pin?

Uh oh, what is a MC pin? I don't recall seeing any pin anywhere. Could you please tell me a little more about the pin?

As always, thanks......

 

[CARtoon]

I'm no expert but I think there should be a bullet shaped rod about 1" that slides into the mc piston before it is bolted to the booster. Maybe someone else can chime in and add to this...

 

[CARtoon]

I think it's called a bore adapter but your booster might not need it. If there wasn't one with your parts, then don't worry about it.

 

[JRouche]

Hmmm, I dont have any additional pins. Its straight from the brake pedal arm to the MC, straight rod. So, the key to tight brakes IMO is when the engine is OFF, for power brakes. Get it tight when its off and they are tight. The deep pedal you feel when you start the car is the booster doing its work. If you have a really tight pedal on the first hit (engine off) then its good to go. Drive it, it will be clamping down. Now a faulty MC will pedal dive when its bypassing, but it doesnt sound like thats what you have. JR

 

[67LOU]

Mc

For whatever reason I had the same issue on the last two cars I put a new booster and MC on , both where aftermarket units bought online by the customer. It sounds like your MC is toast, but I would bench bleed the MC again and bleed the whole system again, might what to make sure your speed bleeders are working correct, try doing front first then rear. If you buy a new master buy a known good brand not one off ebay. Good luck.

 

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Thanks to those helping me through this. After putting yet another new MC on today and bleeding all the lines again, I finally got some braking. I went through about 2 qts. of fluid, constantly making sure the reservior didin't go dry and finally got most of the air out. What a pain. The speed bleeders I picked up at O'Reilly's helped in that I could do this alone. It seems like they worked as advertised. Thanks again,

 

[taz3]

Glad to hear you got it sorted out. When I replumbed my car, I couldn't believe how long it took to get fluid to the rear wheels. I used a vacuum line to draw the fluid through the system.