Location: Scottsdale, Aridzona
(24.251.181.209) | Hey Rico,
Unless your FMC has been retrofitted with disc brakes in the FRONT with drum brakes in the rear . . . your FMC does NOT have a "Proportioning Valve".
If you do have disc/drum brakes . . . that is a custom installation by "some body" and there is no telling what they did or what you are looking at.
If your "Brakes" are STOCK FMC 2900R . . . ie, Brake package from a P500 Ford Delivery Van . . . the brass block you see near the Master Cylinder is a Midland Ross Switch, Brake, Warning . . . Part # MR-201001AV . . . which is shown in Section 9 Service Brakes, Figure 9-1, Item 30 in the FMC Parts Book. That Brake Warning Switch does not exist anymore on the Nets. It's function is stated on Page 4-6, Para 4-9-j, in the FMC 2800R Owner's Manual, and Page 9-6, Para 9-1-d, in the FMC Service Manual.
All the FMC 2900R BRAKE PRESSURE DIFFERENTIAL VALVE/SWITCH does is turn on a Brake Warning Light on the Dash if there is any Differential Pressure between the FRONT Brake supply circuit and the REAR Brake supply circuit. Nothing else. It does not "regulate, control, or proportion" the brake pressure of flow in any way. If the FRONT and/or REAR brake pressure is different upon Brake APPLICATION . . . it turns the Dash Brake Warning Light ON . . . and it remains ON until something resets the DIFFERENTIAL PRESSURE that moved the VALVE one way or the other . . . or you turn the Ignition Key OFF. But the Light will come back on when the Ignition is powered again. I have yet to find anything about "resetting" the Brake Switch if the Dash Light comes ON in any FMC literature or discussions. Note - Setting the Parking Brake is also supposed to turn that same Dash BRAKE Light ON.
I have spent considerable time searching the Nets finding supporting/explanation of what the BRAKE PRESSURE DIFFERENTIAL VALVE/SWITCH really is, and does, and why a FMC 2900R has one.
I have found NOTHING that explains anything FMC, and just gobbledegook with respect to Dodge or GM BIG trucks and/or other Motorhomes from the 70s. However, the Ford Truck (BIG and Pick-up size) guys have been sorting this out among themselves for some time, and it is all on the Nets to review. For a good and SHORT/CONCISE explanation of the BRAKE PRESSURE DIFFERENTIAL VALVE/SWITCH . . . that many name or think, INCORRECTLY, is a brake proportioning valve . . . please see - http://www.fordification.com/tech/propvalve101.htm
If you still think you need to do something with the BRAKE PRESSURE DIFFERENTIAL VALVE/SWITCH . . . remove it, or re O-ring it (link for seals in the Ford link above) or buy something similar from a similar sized Ford BIG Truck, such as - https://www.ebay.com/itm/NOS-1968-FORD-B600-B750-BRAKE-PRESSURE-DIFF... - and cut/grind the bracket off . . . and install it. If you really think you have to have an exact same NEW one . . . take yours apart, measure bore size, then try to find a new or used one with the same internal dimensions. But I don't think "sellers" will respond to any inquiry about "Bore Size".
Greg's #708 came with disc brakes on the front and drums on the rear. He had some issues that he apparently sorted out and in good faith suggested a PROPORTIONING VALVE that he had installed to sort out his DISC/DRUM setup. But, if you do have disc/drum brakes . . . that is a custom installation by "some body" and there is no telling what they did or what you are looking at . . . and you might try the PROPORTIONING VALVE that Greg suggested. Buy again, I think you are "inquiring" about a BRAKE PRESSURE DIFFERENTIAL VALVE/SWITCH. Please let us know just WHAT you have on your FMC
Brake ON ! Lou #120
Shopsdale, Aridzona
Edited by hemi354az 2018-04-01 4:57 PM
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Proportioning Valve Part Number ?
