66 brake master cylinder

[Gary Schisler]

I am in the process of rebuilding my brakes, master cylinder, and rubber brake lines and I have a question concerning the order of the components as they go in the bore of a non-power master cylinder on a 66. When I checked the 66 Chassis Service Manual for a schematic of the components, it shows a slightly different set up, using the example of the "Duo-Servos Brakes" master cylinder. Since this set up is slightly different, I thought that I would check and see if anyone has the proper order in the main body bore. When I took my components out, they came out in the following order: rubber boot, retaining clip, piston with a secondary seal just below the first lip, primary seal which was seated over the spring. The spring has a small copper-colored metal cap attached to one end of it and it was inside the primary cap or seal. I am really questioning whether this metal spring should go in against the far end of the bore, through which the brake fluid is pushed, or should this metal cap go against the primary seal?

Does anyone know for certain or have an exact diagram here? Thank you, Gary

[Joe L.]

Re: 66 brake master cylinder

Gary----

The correct order of assembly for your 1966 non-power master cylinder is as follows:

washer----valve assembly(this may be the "cap" you're talking about)----spring----cup(larger one)----piston----cup(smaller one)----retaining ring

[Joe L.]

Re: 66 brake master cylinder

Gary----

The correct order of assembly for your 1966 non-power master cylinder is as follows:

washer----valve assembly(this may be the "cap" you're talking about)----spring----cup(larger one)----piston----cup(smaller one)----retaining ring

[Wayne M.]

Re: 65/66 non-PS master cyl.

Gary, a few days ago I was going to post the same questions, as I also am in the process of installing a kit in my '65 non-power master cylinder, GM part # 3866446, Bendix # 618690. I removed the identical components in the same order as you described (BTW, the contact face of my 1" dia. piston against the primary seal/cup has a star-shaped thin metal "reed" {to use a musical instrument term} that acts as a check valve to replace fluid that leaks while pressure is on the system lines or calipers).

I checked my '70 Corvette parts manual exploded view and it shows '64-'66 with the washer and valve assembly (which Joe has described) between the spring and the end of the bore (where the fluid exits). I was afraid some previous owner had rebuilt the unit and left out these two components, which, according to the '63 shop manual, are VERY important. But then again, we all know that the '64 master cylinder (and the '65 drum brake cylinder, I believe) were not the same as the disc brake unit. However, by careful reading of the '65 shop manual, Standard Brakes, page 5-5, Main Cylinder, it says that the service operations for "65 (and '66, by extension) remain the same, except that internally, does NOT contain a residual pressure valve. Also, the parts book (under group 4.657) only shows a valve for '63-'65 exc. Disc Brakes. It DOES show a valve seat "washer", but does not specify if also for disc brakes -- if there is no valve, we can assume there is no valve seat washer, and your disassembly confirms my assumption that I'm not missing any parts.

The local Goodwrench couldn't help me with the kit and suggested NAPA. There, after much X-referencing of part #s, I was sold a WAGNER F31066. (equals EIS # 420), which of course contains more parts than I took out, incl. the valve seat and valve (which looks like the center part of the cap off a salt shaker). Probably this kit is intended to service other 1" bore applications that require the check valve and seat.

Hope this helps -- I know your post helped me. If any other '65-'66 non PS owners report that they HAVE the check valve and seat, advise us immediately, before re-assembly.

[Wayne M.]

Re: 65/66 non-PS master cyl.

Gary, a few days ago I was going to post the same questions, as I also am in the process of installing a kit in my '65 non-power master cylinder, GM part # 3866446, Bendix # 618690. I removed the identical components in the same order as you described (BTW, the contact face of my 1" dia. piston against the primary seal/cup has a star-shaped thin metal "reed" {to use a musical instrument term} that acts as a check valve to replace fluid that leaks while pressure is on the system lines or calipers).

I checked my '70 Corvette parts manual exploded view and it shows '64-'66 with the washer and valve assembly (which Joe has described) between the spring and the end of the bore (where the fluid exits). I was afraid some previous owner had rebuilt the unit and left out these two components, which, according to the '63 shop manual, are VERY important. But then again, we all know that the '64 master cylinder (and the '65 drum brake cylinder, I believe) were not the same as the disc brake unit. However, by careful reading of the '65 shop manual, Standard Brakes, page 5-5, Main Cylinder, it says that the service operations for "65 (and '66, by extension) remain the same, except that internally, does NOT contain a residual pressure valve. Also, the parts book (under group 4.657) only shows a valve for '63-'65 exc. Disc Brakes. It DOES show a valve seat "washer", but does not specify if also for disc brakes -- if there is no valve, we can assume there is no valve seat washer, and your disassembly confirms my assumption that I'm not missing any parts.

The local Goodwrench couldn't help me with the kit and suggested NAPA. There, after much X-referencing of part #s, I was sold a WAGNER F31066. (equals EIS # 420), which of course contains more parts than I took out, incl. the valve seat and valve (which looks like the center part of the cap off a salt shaker). Probably this kit is intended to service other 1" bore applications that require the check valve and seat.

Hope this helps -- I know your post helped me. If any other '65-'66 non PS owners report that they HAVE the check valve and seat, advise us immediately, before re-assembly.

[Gary Schisler]

Re: 66 brake master cylinder

As an added note, in careful reading of the disc brakes section of the 66 service manual it states that "The cylinder internally differs only in that it contains a larger reservoir but does not contain a residual pressure valve." The cap that I was talking about is physically attached to the spring by small wrap-around arms that secure it to the first loop of the spring. I think that this metal cap goes against the primary seal, the larger of the two.

Thank you, both for your input.

[Gary Schisler]

Re: 66 brake master cylinder

As an added note, in careful reading of the disc brakes section of the 66 service manual it states that "The cylinder internally differs only in that it contains a larger reservoir but does not contain a residual pressure valve." The cap that I was talking about is physically attached to the spring by small wrap-around arms that secure it to the first loop of the spring. I think that this metal cap goes against the primary seal, the larger of the two.

Thank you, both for your input.