1980 master cylinder casting numbers

[Mark A.]

The Judging Manual for the 1980 Corvettes, says there are casting numbers on the master cylinder, but does not say what they are. If someone out there could pass along the info, I would appreciate that. Mark

[Joe L.]

Re: 1980 master cylinder casting numbers

The Judging Manual for the 1980 Corvettes, says there are casting numbers on the master cylinder, but does not say what they are. If someone out there could pass along the info, I would appreciate that. Mark

Mark------


As far as I know, it was 5460346 (but I'm not 100% certain).

However, all master cylinder of this casting number are not the same. Some are machined for bleeder valves; some are not. Some have standard SAE mounting holes; some are metric. Assuming I'm correct on the casting number, the one you need has no bleeders and metric mounting holes. However, the mounting holes mean very little since I believe that either standard or metric bolts will work and the actual size is not discernible when bolts are installed.

[Mark A.]

Re: 1980 master cylinder casting numbers

Thank you Joe.

[Mark F.]

Re: 1980 master cylinder casting numbers

Mark------
As far as I know, it was 5460346 (but I'm not 100% certain).

However, all master cylinder of this casting number are not the same. Some are machined for bleeder valves; some are not. Some have standard SAE mounting holes; some are metric. Assuming I'm correct on the casting number, the one you need has no bleeders and metric mounting holes. However, the mounting holes mean very little since I believe that either standard or metric bolts will work and the actual size is not discernible when bolts are installed.

Hi Joe,

Maybe a dumb question, but how does one properly bleed/setup a Master Cylinder that doesn't have a bleeder valve (let's say for a complete purge and replacement of brake fluid) ?

Or are you saying the bleeder valve is there - but the boss (or recessed area) it goes into is threaded but not machined flat ?

[Joe L.]

Re: 1980 master cylinder casting numbers

Hi Joe,

Maybe a dumb question, but how does one properly bleed/setup a Master Cylinder that doesn't have a bleeder valve (let's say for a complete purge and replacement of brake fluid) ?

Or are you saying the bleeder valve is there - but the boss (or recessed area) it goes into is threaded but not machined flat ?

Mark------


I believe the bleeder valves were intended for convenient on-car master cylinder bleeding. However, the bleeder valves were virtually useless for bleeding the master cylinders and I expect that's why they were eliminated. To bleed a master cylinder, on-car or off-car, the brake lines are disconnected and a bleeder kit used to bleed the master cylinder from the outlet ports. Bleeder kits are quite inexpensive or can be made-up if one so wishes.

The bleeder valve surfaces of the master cylinder were never machined on any 1967+ master cylinders; the bleeders were machined (essentially just drilling, tapping, and valve seat machining) directly into the natural, as-cast surface. Beginning sometime in 1973, the bleeder valve surfaces remained but no valve machining was done. The 5460346 master cylinder casting always had the bleeder valve surfaces. Other castings, which may or may not have been used in PRODUCTION and available in GM SERVICE, did not. Most, if not all, aftermarket castings do not have the bleeder valve surfaces. I do not believe that any 1967+ master cylinder casting except fairly recently available reproduction castings have been available with bleeder valve surfaces or bleeder valves for many years. In fact, I think that the 5460346 was the last GM casting to have the bleeder valve surfaces.

[Mark F.]

Re: 1980 master cylinder casting numbers

Thanks for the detailed explanation, Joe,

It's been a long time since I bench-bled my Master Cylinder after a rebuild by Lonestar.

As I recall, I rigged up my own tubing to do the bench bleed job in my vice, but I can't remember if I ever used the bleeder on the MC after that or not.

Brakes have always worked great, so no occasion to have to do it again I guess...

[Tom R.]

Re: 1980 master cylinder casting numbers

Hi Joe,

Maybe a dumb question, but how does one properly bleed/setup a Master Cylinder that doesn't have a bleeder valve (let's say for a complete purge and replacement of brake fluid)?

See if this helps...YouTube Video.

https://www.youtube.com/watch?v=3PHVXFcdMk4

Another handy tool is the Motive Pressure bleeder. I fabricated a plate that replaces the M/C cover and with a huge C clamp, I use it to bleed the brakes.

https://www.zip-corvette.com/92-19-motive-power-brake-bleeder.html?msclkid=68585f159beb1475c2983a784e15ff48&utm_source=bing&utm_medium=cpc&utm_campaign=Smart%20Shopping%20%7C%2011%2F10%2F23&utm_term=4586612760303303&utm_content=All%20Products

[Mark F.]

Re: 1980 master cylinder casting numbers

See if this helps...YouTube Video. https://www.youtube.com/watch?v=3PHVXFcdMk4
Another handy tool is the Motive Pressure bleeder. I fabricated a plate that replaces the M/C cover and with a huge C clamp, I use it to bleed the brakes. https://www.zip-corvette.com/92-19-m...All%20Products

Interesting method on the YouTube, Tom,

And the two bleeder valves on the side of the MC weren't mentioned.

So, as Joe said, why have them there if they are not used ?
Probably why they were eventually eliminated.

[Joe L.]

Re: 1980 master cylinder casting numbers

Interesting method on the YouTube, Tom,

And the two bleeder valves on the side of the MC weren't mentioned.

So, as Joe said, why have them there if they are not used ?
Probably why they were eventually eliminated.

Mark------

I've never been able to figure out why the master cylinder bleeder valves are an ineffective means to bleed the master cylinder. Intuitively, they seem like they would be the perfect way to bleed the master cylinder.

[Mark F.]

Re: 1980 master cylinder casting numbers

Mark------

I've never been able to figure out why the master cylinder bleeder valves are an ineffective means to bleed the master cylinder. Intuitively, they seem like they would be the perfect way to bleed the master cylinder.

Joe,

My '67 Chassis Service Manual has no mention of using these during both bleeding procedures described (Pressure or Manual).

Mine also doesn't even show the bleeders in any of the cross-section figures or photographs.

Looking at the geometry of where the two bleeders are they seem to be at the top of the front and rear circuit pistons, which is where I would think a bubble in either line that high up in the system would logically come to rest. If a bubble was in there, pressing the brake pedal would certainly squeeze it out; as would the pressure bleed equipment if those bleeders were opened.

Somebody out there knows

[Joe L.]

Re: 1980 master cylinder casting numbers

Joe,

My '67 Chassis Service Manual has no mention of using these during both bleeding procedures described (Pressure or Manual).

Mine also doesn't even show the bleeders in any of the cross-section figures or photographs.

Looking at the geometry of where the two bleeders are they seem to be at the top of the front and rear circuit pistons, which is where I would think a bubble in either line that high up in the system would logically come to rest. If a bubble was in there, pressing the brake pedal would certainly squeeze it out; as would the pressure bleed equipment if those bleeders were opened.

Somebody out there knows

Mark------


As far as I know, all original 1967-72 Corvette master cylinders, standard or power brake, had the bleeder valves.

The reasons that you described are EXACTLY why I had always figured the bleeder valves would be the ideal place to bleed the master cylinder. But, I never had a bit of luck using them and others regularly report the same experience.

[Mark A.]

Re: 1980 master cylinder casting numbers

While we are at it, how about the casting numbers for the calipers? They also are not listed, or even mentioned in the Judging Manual. Does this mean that the judges will not be looking for casting numbers for Survivor Judging?

[Tom R.]

Re: 1980 master cylinder casting numbers

While we are at it, how about the casting numbers for the calipers? They also are not listed, or even mentioned in the Judging Manual. Does this mean that the judges will not be looking for casting numbers for Survivor Judging?

Correct...not visible

But the M/C cast number is verified.

[Patrick H.]

Re: 1980 master cylinder casting numbers

Does this mean that the judges will not be looking for casting numbers for Survivor Judging?

You would have to ask the Bloomington judges about Survivor judging.

[Joe L.]

Re: 1980 master cylinder casting numbers

While we are at it, how about the casting numbers for the calipers? They also are not listed, or even mentioned in the Judging Manual. Does this mean that the judges will not be looking for casting numbers for Survivor Judging?

Mark------

All caliper casting numbers from about mid/late 1973 through 1982 are the same and all begin with "547". If your calipers meet this, they are the original casting numbers although not necessarily original to the car.