Adjustable Brake proportioning valve

[Scrub]

Today I towed a bobcat excavator home. Pretty heavy. Just for grins, I slammed the brakes on to see what was happening and I could make the front tires slide, but the rears didn't seem to do anything. Might have something to do with the rear axle bouncing on the frame making the front light and the back sucked down pretty tight to the pavement.

I have a thread up about Hydro boost master cylinders, but know I am wondering about the proportioning valve I have. It came off the donor truck that had the 2wd 1-ton front end that I have. It bolts to the crossmemer under the radiator.

I know the newer trucks have and adjustable proportioning valve that is hooked up to the rear axle and puts more brake to the rears when the rear springs are lowered by a heavy load.

Anyone know anything about these?

Thanks in advance

TW Scannell

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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.

[This message has been edited by Scrub (edited May 19, 2002).]