Brake problems, possible booster!

[94CobraPace]

Hey, I am restoring a 69 Mach I & just got the engine in last week. Started it up & runs good. Now the brake pedal goes almost to the floor. I replace the master cylinder & the problem is still there. I blead the brake system after bench blead the master cylinder prior to installation. The brakes can hardly stop the rear wheels while up on jack stands.
Is this the brake booster?
Thanks

 

[68 Coop]

Did you set the adjustment wheel??? It's the long screw that has the wheel toward the middle of the screw, that goes in at the bottom of the brakes, and you can adjust them with a screwdriver.

 

[Platonic Solid]

Your Booster could be damaged if brake fluid was leaking out of the rear of the old master cylinder.

(Just to cover this base) Did you blead the brakes in the right order = longest line first, shortest last? Usually: RR, LR, RF, LF.

Are you sure there's no leaks in the system? Have you inspected (better yet, replaced , since they're fairly inexpensive) the rear wheel cylinders?
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[351carlo]

I went through 3 master cylinders on my 70 before I got one that wasn't defective out of the box.

I hope you bench bled your master cylinder.

 

[94CobraPace]

Yep, bench bled the master cylinder. I purchased a new master cylinder. The rear brakes were working fine when parked & they have not been touched. Blead the brakes in the order, RR, LR, RF the LF. No leaks in the system. The front calipers were rebuilt & no leaks there.
When the brakes are pressed with the engine on, they feel the same, that is why I think it is the brake booster.
Thanks for the replys, anyone or thing else?

 

[Edbert]

Disconnect the vacuum line (and plug it) to the booster and see if it behaves differently. Just as a diagnostic.

 

[Platonic Solid]

... The rear brakes were working fine when parked & they have not been touched. ...

Using that logic, the whole brake system should work just fine . . . but it doesn’t.
I would still suspect the low cost rear wheel cylinders before the high cost booster.
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