66 Corvette Power Brake Master Cylinder

[Charles W.]

I have a 66 PB master cylinder and it has a small allen head plug recessed about 1/2" in the front boss of the master cylinder.

I looked at very original 66 car and its PB master cylinder just had a blind hole at the bottom of this front boss (no plug).

I talked to a rebuilder and he said he had 5 cores and they all had small allen head plugs recessed in the front boss.

Is the allen plug configuration possibly a design change that GM made or is it a modification that someone has made over the years for whatever reason?

Would the allen plug in the master cylinder be considered incorrect by an NCRS Judge?

Thanks in advance for any information on this issue.

Charlie

[Dave B.]

Re: 66 Corvette Power Brake Master Cylinder

Charlie,
My March 4 built '66 has the blind hole in the front boss. Believe it is original. Haven't heard about judging. One of the experienced judges might join in.
Regards,
Dave

[Richard S.]

Re: 66 Corvette Power Brake Master Cylinder

Charles,

My June 10th,1966 big block has it's original power brake master cylinder. There is no plug in the hole......

[ken edmunds]

Re: 66 Corvette Power Brake Master Cylinder

I had a 66 power brake master rebuilt by White Post Restorations in 1986. When the piston is frozen in the bore, they drill a hole in the front to press the piston out and then thread the hole and put a plug in it. Perhaps this is the situation with yours.

[Rob A.]

Re: 66 Corvette Power Brake Master Cylinder

Charlie,

I have an original '66 p.b. master cylinder. If you're referring to the recess in the very front of it, in line with the piston, mine has the recess, but no plug of any kind.