66 PB master cylinder opinions needed

[Joe L.]

Re: 66 PB master cylinder opinions needed

Thanks for the catch Jeff, since I have this M/C in hand I just checked it and it does have varying thickness on the cap machined area. Caliper readings on the front fill area varies between 0.142 to 0.185 the rear is 0.170 to 0.201 . Again I want to thank you as I would like confirm its original, so far I'm leaning too its correct, Pros- the pitting under the caps on the machined surface and the brass inlets don't look new. Cons- the mold parting line looks to nice but when looking on the inside looks more miss matched and pronounced. This could be one of those old repops Dick metioned or OEM replacement or a cleaned up original, but I'm pretty sure now its not a new repop by Corvette Stainless Steel Brakes. Any other comments are more than welcome

Brian------


Most of the feature differences that have been pointed out (e.g. parting line flash differences) are features that could easily have varied over the period that these master cylinders were manufactured by GM/Delco Moraine. They could also have varied at any given time during manufacture since there was likely more than 1 pattern used.

One thing that I noticed in your first set of photos and I see again in your latest set which led me to believe that this is a GM/Delco Moraine piece is the piston stop screw. This appears to me to be an original screw. 1967+ usually used a stop screw with a trimmed ("non-indented") head. I believe (but I'm not 100% sure) that the 65-66 PB master cylinders used an untrimmed (i.e. "indented" head) screw.

[Russ S.]

Re: 66 PB master cylinder opinions needed

Brian------



Most of the feature differences that have been pointed out (e.g. parting line flash differences) are features that could easily have varied over the period that these master cylinders were manufactured by GM/Delco Moraine. They could also have varied at any given time during manufacture since there was likely more than 1 pattern used.

One thing that I noticed in your first set of photos and I see again in your latest set which led me to believe that this is a GM/Delco Moraine piece is the piston stop screw. This appears to me to be an original screw. 1967+ usually used a stop screw with a trimmed ("non-indented") head. I believe (but I'm not 100% sure) that the 65-66 PB master cylinders used an untrimmed (i.e. "indented" head) screw.

I have an original over the counter master cyl that I bought in 1980 from GM and it doesn't have a piston stop screw.

[Brian K.]

Re: 66 PB master cylinder opinions needed

Thanks Joe, You convinced me its real! Your knowledge and insight is a real treasure to your fellow NCRS members! Thank you again.

Brian------


Most of the feature differences that have been pointed out (e.g. parting line flash differences) are features that could easily have varied over the period that these master cylinders were manufactured by GM/Delco Moraine. They could also have varied at any given time during manufacture since there was likely more than 1 pattern used.

One thing that I noticed in your first set of photos and I see again in your latest set which led me to believe that this is a GM/Delco Moraine piece is the piston stop screw. This appears to me to be an original screw. 1967+ usually used a stop screw with a trimmed ("non-indented") head. I believe (but I'm not 100% sure) that the 65-66 PB master cylinders used an untrimmed (i.e. "indented" head) screw.

[Brian K.]

Re: 66 PB master cylinder opinions needed

Thanks Russ for the info, sincerely Brian

I have an original over the counter master cyl that I bought in 1980 from GM and it doesn't have a piston stop screw.

[Glen C.]

Re: 66 PB master cylinder opinions needed

Brian

In addition to the mold parting line seam mentioned by Bob Taylor's response, the original m/cyl has eccentric & varying wall thickness on the filler cap bosses. See photos of my original (Jul '66 car) below. I'd say your photos are not of an original part.

Jeff

Jeff, I would raise the same question & for the same reasons!
My 66 PBMC with the caps removed looks like the one you have pictured. My casting seam between the filler boss openings is raised and rough, like your photo. In addition, the threaded openings are offset in an identical position, as you described. Inboard toward the engine, like your photo.