Proportioning Valve
Like Wayne stated, stock 4 wheel drum cars use what is actually a distribution block that has no proportioning function to it.
4 wheel drum cars, as well as cars fitted with 4 wheel discs, need NO proportioning valve. The drum cars rely on wheel cylinder sizing to establish the brake proportioning bias. Same applies to the 4 wheel disc systems.
Front disc/rear drum cars DO need some manner of proportioning so that each end of the car gets the proper line pressure. Wheel cylinders require much less pressure from the master cylinder to energize. Disc brake calipers are much bigger and require more pressure and fluid volume to operate. The factory 4 wheel drum distribution block looks like this:
The proportioning valve looks like this:
Like Wayne stated, stock 4 wheel drum cars use what is actually a distribution block that has no proportioning function to it.
4 wheel drum cars, as well as cars fitted with 4 wheel discs, need NO proportioning valve. The drum cars rely on wheel cylinder sizing to establish the brake proportioning bias. Same applies to the 4 wheel disc systems.
Front disc/rear drum cars DO need some manner of proportioning so that each end of the car gets the proper line pressure. Wheel cylinders require much less pressure from the master cylinder to energize. Disc brake calipers are much bigger and require more pressure and fluid volume to operate. The factory 4 wheel drum distribution block looks like this:
The proportioning valve looks like this:
