73 M300 Brake Proportional Valve Replacement advice.

[Bonebag]

Hi..getting closer to getting on the road. I am halfway through rebuilding the Kelsey Hayes proportional valve for the disk brake conversion and noticed the piston sleeves are pretty pitted. I'm kind of at a loss as for trying to find a replacement that's OEM and not really sure where to look for aftermarket as there seems to be plenty of options but no real solid advice or guidance. The brake system is the 73 master vac system with rear drum from a D18. Thanks for any help.

[DaveVA78Chieftain]

From Dodge MH Service Manual:
1. For Front disc/Rear drum systems, Dodge used a Combination Brake Warning Switch / Metering Valve.

  A. Brake Warning switch portion: The brake warning switch used in these combination valves are latching types. If a pressure loss occurs in one side of the dual brake system the piston in the valve will move toward the failed side and latch in that position. This will cause the brake system warning light to come on and stay on until the brake system is repaired. After repairing and bleeding the brake system, applying the brakes with moderate force will hydraulically re-center the piston and automatically turn off the warning light.

  B. Metering valve portion: The metering valve holds off hydraulic pressure to the front disc brakes in the 35 to 135 psi range to allow the rear drum brake shoes to overcome the return springs and begin to contact the drums. This feature helps prevent locking the front brakes on icy surfaces under light braking conditions. The metering valve has no effect on front brake pressure during hard stops. Design cut in is 117 psi.

If no longer available, then start by trying Master Power Brake.  They have a good video describing this type of valve youtube.  Only difference with that video to you setup is the proportional valve portion which I think is equivalent to the residual valve installed in your master cylinder.  If they cannot support the heavy rig application (1 ton chassis) then hopefully they can refer you to someone who can.

1969 - 1977 Dodge MH Service Manual ref data:

1973 & Later M300 / M400 (RM350) / M500 (RM400) / M600 Dodge Motorhome Brake Reference Data

Combination Metering Valve / Brake Warning Switch

1973-74 Dodge Class A RM300 Motorhome Brakes