66 Power Master Cylinder or is it a 65?

[Donald H.]

I know the information I need is somewhere here on the TDB, but I have been searching all morning and can't find it.

I have a power master cylinder that came with my 66 when I bought the car. The car now has an aftermarket master cylinder on it.

I have included some pictures of the master cylinder. I'm trying to determine if it is a correct 66 power master cylinder.I think I read somewhere on the forum that 65 and 66 had different sized brake lines going into the master cylinder. Is that correct? and if so, is there a way to measure the inlet holes (threaded holes) on the one I have pictured to determine whether it is a 65 or 66?

Also, I have included a picture show down into the chambers. The front/forward chamber has a small threaded hole (blue arrow). What goes into this hole? If it is some type of screw, where can I get one and what is the purpose?

Thanks,
Don

[Donald H.]

Re: 66 Power Master Cylinder or is it a 65?

Found part of what I was looking for. Found that the 65 has 3/16" line and the 66 had 1/4". Is there an easy way to tell my looking at the inlet holes on the master cylinder?

Another probably dumb question. When referring to the brake lines, is the 3/16" and 1/4" ID or OD?

Thanks,

Don

[Jeffrey R.]

Re: 66 Power Master Cylinder or is it a 65?

Don
The master cylinder I included with the car is 1/4" and correct for a 66. The holes on a 65 cylinder are much smaller and you can tell the difference by eye.
Hope you are happy with the car. Have you done anything to it since you bought it?
Jeff

[Donald H.]

Re: 66 Power Master Cylinder or is it a 65?

Don
The master cylinder I included with the car is 1/4" and correct for a 66. The holes on a 65 cylinder are much smaller and you can tell the difference by eye.
Hope you are happy with the car. Have you done anything to it since you bought it?
Jeff

Yes, happy with the car. I've actually done a number of things. Fixed all the electrical things, e.g. back up lights, horn, turn signals. Restored/repolished the top shielding and installed it.

[Joe L.]

Re: 66 Power Master Cylinder or is it a 65?

I know the information I need is somewhere here on the TDB, but I have been searching all morning and can't find it.

I have a power master cylinder that came with my 66 when I bought the car. The car now has an aftermarket master cylinder on it.

I have included some pictures of the master cylinder. I'm trying to determine if it is a correct 66 power master cylinder.I think I read somewhere on the forum that 65 and 66 had different sized brake lines going into the master cylinder. Is that correct? and if so, is there a way to measure the inlet holes (threaded holes) on the one I have pictured to determine whether it is a 65 or 66?

Also, I have included a picture show down into the chambers. The front/forward chamber has a small threaded hole (blue arrow). What goes into this hole? If it is some type of screw, where can I get one and what is the purpose?

Thanks,
Don

Don-----


The tapping in the forward reservoir is for a piston stop screw. It is not essential to install this screw and many rebuilders delete it. The screw is long-since GM discontinued. If you want to obtain one, you'll need to salvage one from a master cylinder core. They were used on many different Delco-Moraine master cylinders so you don't need to obtain one from a 65-66 Corvette PB master cylinder. A photo of an original screw is attached. For info, the thread size is #10-24. The thread length is 3/16" and the pin length is 1/4".


DSCN2819.jpgDSCN2820.jpg

[Jeffrey R.]

Re: 66 Power Master Cylinder or is it a 65?

Don
I'm glad you are happy with the car. It was a pleasure dealing with you and you are a very honest guy. (that mix up with the wire transfer caused by my bank would have given me some sleepless nights if you hadn't called to tell me about it before my bank did). Are you going to rebuild the cylinder soon and install it? By the way that hole you marked with the blue arrow is for a hex head pin that is threaded near the head. It holds the front piston in the bore and possibly limits the travel of that piston. I think the pin is included in the complete rebuild kit (the one that has all the parts pistons,springs,seals etc not the kits that just have the seals).
Jeff

Sorry I just noticed Joe lucia described the pin while i was typing.

[Donald H.]

Re: 66 Power Master Cylinder or is it a 65?

Thanks for the replies