Adjustable Brake proportioning valve

[Scrub]

I'm not sure which year I saw it, But I know my buddy's full size chevy pickup had one on the rear axle. It had to be in the early 1990's. It was a corp 14 axle with drums.

I just saw an article in Petersen's 4WD mag where Christian Hazel put a lift kit on a Toyota 4-runner and the lift caused the proportioning valve to turn the rear brakes mostly off. This is a pretty common setup.

I am more interested in an aftermarket adjustable proportioning valve, but I don't seem to ba able to find one.

Thanks again


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Scrub
70 GMC 1,000,000 + miles
72 K-20 project, 456 Dana60 front, Corp14 rear w/locker, 265R19.5 tires 20-ply. Warn 12k winches both ends, Cross-over steering with raised tie-rod, Powerbox steering, 4500 watt 120-AC power, Air, Hydraulic aux power, 4 inch lift, 5000 lb air-bags both ends.