MCPV-1 adjustment issues

[doiton3]

Anyone else had trouble with setting the MCPV-1?

I have a 1968 C10 short bed
350 th350
255-60-15 in front 275-60-15 in rear BFG radial T/A - new
Stock rear drum brakes 11"x2"
Front disk kit from CPP CP4CK-6
3" drop spindles in front 4 inch drop springs in the rear.
All new hard lines and rubber lines.
MCPV-1 master


I bench bled the master
Bled each wheel starting at the farthest away.

Tested and adjusted re-bled each wheel.

The MCPV-1 is adjusted
Full forward bias (Large hex full counter clockwise)
Small hex full clockwise then backed off a small fraction.

The rear brakes are still locking up way before the fronts do, any
suggestions?

If I set the small hex full clockwise the fronts will lockup.

[doiton3]

Removed the front metering valve and re-bench bled the master, re-installed the metering valve and re-bled everything.
Rears still lock up with hard braking

For now I have set the small hex (pressure adjustment) to full clockwise, no rear pressure.

Maybe the master is bad, wish CPP had disassemble/rebuild instructions so I could feel more comfortable pulling the proportioning/pressure valve for inspection.

[doiton3]

I beveled the leading and trailing edge of the rear brake shoes and now I can give the rear brake some pressure, they are useable.

I would not recommend this master cylinder for short beds with front disk and rear drum brakes, the rear pressure adjustment is too coarse.

[Lee H]

What shape are your shoes in? I went though a similar issue a few years ago, after many frustrating hours, changing MC & PV, rear cylinders. I changed the seemingly good looking shoes with only a miles for a set of Wagner (riveted) shoes and that cured the problem.

[doiton3]

Brand new shoes, wheel cylinders, springs and hoses.