Problem with brake master cylinder

[minifridge1138]

Hello everyone,

My brake master cylinder was leaking where it attached to the vacuum booster.
Replaced it with a new one.
Then the trouble began.

Bench bleeding went fine.

Bleeding the rear wheels was completely normal.

I had trouble when I got to the front.

We could pump the pedal and build pressure.
We would open the bleeder valve and the pedal sank to the floor very, very slowly.
We closed the bleeder valve.
Then there was no pedal at all. It just sank to the floor as if there was full of air.
If we waited 2-3 minutes and did nothing, then the pedal became firm.
It just continued to do this.

Both front wheels were like this.

Started the car, pedal was soft like it had air in it.

Is there some trick to bleeding the brakes after replacing the master cylinder or did I get a defective master cylinder?

Thanks everyone!!!

 

[6880 Mike]

I'm wondering whether your new master cylinder is bad right out of the box. Stranger things have happened.

 

[mkapp7879]

NEW? or rebuilt? I've always been leery of rebuilt master cylinders.

 

[minifridge1138]

this is new, not rebuilt.
For brakes I usually avoid anything that is rebuilt.

 

[minifridge1138]

Well, I give up.
I'm going to return it and get my money back.

Thanks Everyone!!!

 

[ladams]

I had 2 bad MC's last year and finally went to a different manufacturer. They were pumping fluid from my rear res. to my front res. causing it to overflow in the front and completely losing the rear brakes.

 

[TimAT]

Another little tip- when you bench bleed a m/c, don't bottom the piston out, only give it an inch or so of travel. sometimes they don't finish the honing all the way to the bottom and it cuts the seals.

 

[minifridge1138]

Where did you get the defective ones?

Where did you get a good one?