Can't Stop

[uscrichter]

I just finished a full restoration on my'68 SS Vert with factory rebuilt disc brakes and had everything working good when I assembled everything about a year ago and then brought it back to my painter to touch a few are areas after final assembly, the problem is that the brake pedal went to the floor after sitting for that time and found a small leak at the proportioning valve located under the driver door which I tightened successfully, and after bleeding the brakes had some resistance but the pedal still goes all the way down to the floor and I have bleed the master cylinder and all of the brakes numerous times and I'm at my wits end on this one!  I have restored numerous cars over the last 40 years and never ran into this before, I had everything professionally rebuilt and is factory and see no leaks anywhere...help please, any ideas?

[jdv69z]

Master Cylinder failure?

[uscrichter]

How can I check it? I bought it several years ago from HBC Camaro supposed to have been rebuilt.

[1stgen68]

Maybe the Master Cylinder piston seals. When you are pressing on pedal and it's going to the floor, it may be burping air right out of the master at the same time. Have someone look to verify this at the same time when you are pushing. If there's no pressure, then there's air. If there's air then it's going somewhere out the system and the first culprit is the Master Cylinder.

[1stgen68]

And another thing!! Stay away from Advance and Auto Zone rebuilt Master Cylinders that are 40 bucks. Freaking garbage. About to put the 4th one in a year on mine and this time is because it's leaking between the bore and the booster.  Get a net new one.

[uscrichter]

Thanks for the advice, I will take it out and bench bleed the MC and if that doesn't work, I'll get it sent back out for rebuilding since it is an original MC with matching numbers and the car is restored to original so I wont be using after market parts, sounds like the MC is the problem, sure is frustrating and expensive...hate having to redo what should have already been done!

[1stgen68]

If you see bubbles during or post bench bleed, RED FLAG!!!!

[uscrichter]

Thanks again for the help!
Curt