70 C20 Master Cylinder & Booster Replacement

[CW4B]

Original set up has a “Prod Distributor & Switch Ass” that didn’t come with the KORN772 drum/drum “Power Brake Conversion Kit” I purchased from Brotherstruck.com. Although configured a bit differently, Brothers calls that a Proportioning valve. I learned that the kit didn’t come with the proportioning valve because I selected drum/drum, which is what I’m running (original) Rub is current brake lines don’t terminate where they need to to fit new m/c without proportioning valve, but even with their proportioning valve, I believe I would need three brake lines instead of current two terminating at m/c. One for left front, one for right front, one for rear.

What should I do?

[AussieinNC]

Look up

http://www.lmctruck.com/icatalog/cb/full.aspx?Page=138

On a drum / drum truck, there is no proportioning valve. The brake lines come from master cylinder into a distribution block fitted with a brake circuit warning switch...see pic

It shows two lines into the distribution block, two lines from valve to front cross member, where one line continues to rear and the other is split using a T union to feed both front wheels....I believe the T union LMC number is 30-1408.

[jocko]

Did you purchase a master cylinder for a C10 or a C20? They are different. Use your original distribution block/switch Assembly (as long as you have not converted to Disk/Drum), ensure you have the correct master cylinder for the size truck you have (C10 and C20 have different MC-to-distro block lines and conventions), and then buy or bend the appropriate lines for the C20 that go from MC to distro block.

[randy500]

If you buy the factory power brake booster all you have to do is bolt the current master cylinder with lines attached to the booster, no brake bleeding, etc.

Even with your crappy repro booster you still should be able to just stretch the master cylinder with distribution block and lines forward and attach to the booster.

There are 2 basic styles of master cylinders and boosters...shallow and deep master cylinder push rod holes with corresponding boosters, some boosters are dual diaphragm, some single, they all have reasonably close boost effect.

You should check the master cylinder hole depth/pushrod clearance using a special tool, most people dont and it usually works out fine.

[2 Stovebolts]

Reading the C10 & C20 have different boosters....are the C20 & C30 the same?

[CW4B]

Originally Posted by AussieinNC

Look up

http://www.lmctruck.com/icatalog/cb/full.aspx?Page=138

On a drum / drum truck, there is no proportioning valve. The brake lines come from master cylinder into a distribution block fitted with a brake circuit warning switch...see pic

It shows two lines into the distribution block, two lines from valve to front cross member, where one line continues to rear and the other is split using a T union to feed both front wheels....I believe the T union LMC number is 30-1408.

That is exactly what I have (the distribution block). Mine is pretty rusted and because it has a switch of some kind in it, I am hesitant to try and refurbish it. Don't see it in LMC, so will look elsewhere for it. Thanks so much!

[CW4B]

Originally Posted by AussieinNC

Look up

http://www.lmctruck.com/icatalog/cb/full.aspx?Page=138

On a drum / drum truck, there is no proportioning valve. The brake lines come from master cylinder into a distribution block fitted with a brake circuit warning switch...see pic

It shows two lines into the distribution block, two lines from valve to front cross member, where one line continues to rear and the other is split using a T union to feed both front wheels....I believe the T union LMC number is 30-1408.

Hmm. Do you know if this will work?
http://www.classicperform.com/Store/...ings/PR107.htm

Also, this is the part I purchased to replace the boost and M/C from Brothertrucks.com. I selected the "drum/drum" option, which causes it to ship without the proportioning valve which I later learned is because a proportioning valve isn't needed for drum/drum set ups. But a distribution block is, but neither Brothers or LMC sells it. So I landed on classicperform.com...
https://www.brotherstrucks.com/1967-...tinfo/KORN772/

[May70]

Following this one. My c20 will need serious brake work.