[Keith Seymore]

Originally Posted by Keith Seymore

Here's the brake chart for 1982, for full size truck:



The brake RPOs are driven by 1/2, 3/4 and one ton models, in two and four wheel drive, with various wheelbases and GVW ratings, and manual vs vacuum boost vs hydraulic boost.

We were required to attend occasional peer review sessions with the passenger car guys.

They would put their one brake system up, to cover Y car, or their two systems to cover X car or J car, and go through them.

They asked "how come you truck guys never review your systems here?".

So at one of the following meetings we put that brake chart up and started walking through it.

After a session of that they were like "it's ok. You guys don't have to review your stuff here".

[scott06]

Originally Posted by 67Lemons

So there’s a different master cylinder for disc vs drums even without power?

the volume of brake fluid to move a caliper piston vs a wheel cylinder is what drives the change in Master Cylinder bore diameter

[Scarebird]

Originally Posted by scott06

the volume of brake fluid to move a caliper piston vs a wheel cylinder is what drives the change in Master Cylinder bore diameter

Not true.

A caliper piston while having a much larger surface area only moves a small amount. A drum cylinder moves quite a bit. so the actual volume is almost the same - at least for GM's of our era...

The reason a disc master has such a large reservoir is as the caliper pad wears that much more fluid is pulled into the caliper to make up for the piston travel.

[scott06]

Originally Posted by Scarebird

Not true.

A caliper piston while having a much larger surface area only moves a small amount. A drum cylinder moves quite a bit. so the actual volume is almost the same - at least for GM's of our era...

The reason a disc master has such a large reservoir is as the caliper pad wears that much more fluid is pulled into the caliper to make up for the piston travel.

from master powers tech FAQ page -https://mpbrakes.com/support/faqs/?srsltid=AfmBOooCqQvljLczun_CETtwTACaghY1XXgEzKSvB vQ9iia5jNLqFZU-#1656435684989-5ec775fd-ea5a

not the greatest snip but you get the idea

[RocktimusPryme]

Originally Posted by scott06

from master powers tech FAQ page -https://mpbrakes.com/support/faqs/?srsltid=AfmBOooCqQvljLczun_CETtwTACaghY1XXgEzKSvB vQ9iia5jNLqFZU-#1656435684989-5ec775fd-ea5a

not the greatest snip but you get the idea

Ill defer to the experts if Im wrong, but Im not sure that 10lb residual is accurate for the masters most of us are talking about here.

From what I understand the necessity of the ~10ish pound residual pressure valves (or 2 for disc setups) is aimed at 50's and older vehicles where the master was mounted below the floorboard. When you have the master high on the firewall I think that removed a lot of the need for high pressure residual valves. Drum masters meant for firewall installation may have some residual valving depending on the application, but I don't think they have 10 lb valves.

[Scarebird]

Originally Posted by RocktimusPryme

From what I understand the necessity of the ~10ish pound residual pressure valves (or 2 for disc setups) is aimed at 50's and older vehicles where the master was mounted below the floorboard.

That is correct from what I have seen. Very few master cylinders from the mid 60's on had integral residual valves - and those were usually Mopars.

[scott06]

Originally Posted by RocktimusPryme

Ill defer to the experts if Im wrong, but Im not sure that 10lb residual is accurate for the masters most of us are talking about here.

From what I understand the necessity of the ~10ish pound residual pressure valves (or 2 for disc setups) is aimed at 50's and older vehicles where the master was mounted below the floorboard. When you have the master high on the firewall I think that removed a lot of the need for high pressure residual valves. Drum masters meant for firewall installation may have some residual valving depending on the application, but I don't think they have 10 lb valves.

Makes sense, certainly the comment on MP page is generic.

Would certainly think unless you really know what you are doing most of us would be better getting a kit vs trying to piece it together.