Testing a Proportioning Valve?

The factory bias on these cars was pretty heavily to the rear, they always lock the rear up first and by a pretty substantial amount. Redfish described some of the reasoning but on most of the factory cars I’ve driven the rear bias is too much even with those considerations. It’s like the factory about of understeer- sure, the factory assumes the general public can’t drive so they set cars to under rather than oversteer, but in the 60’s and 70’s they really got carried away.

The proportioning valves can be “reset”, that’s why the FSM describes the brake bleeding process as being passenger rear, drivers rear, passenger front, drivers front. Follow that order and the prop valve should end up “set” properly.

But as Mattax pointed out any changes from factory specs may change the needed bias. The most common thing is people run staggered wheel set ups on these cars, which changes things a lot in the braking department. Changing the wheel cylinder bores can help, or just install an adjustable proportioning valve.