A '74 2WD Ford F100 would have had the cast iron Kelsey-Hayes metering, pressure differential, proportioning valve, like I posted a picture and Ford diagram of in my previous post.sargentrs wrote:Thanks for the lesson, Steve! So, to us laymen, if we've swapped over to front disc brakes from a '74 (like me), we should source a proportioning valve for a '73+ with disc/drum and the equivalent m/c? If unable to find one, the same '73 Mustang disc/drum prop valve would work too? This is one of the big gaping holes in my swap that I have yet to get a definitive answer.
A Mustang disc/drum brake valve would not have the same proportioning valve spring rate in it as a valve for a Ford truck. An early Mustang would be lighter than a (heavier) truck. Proportioning in a Mustang integrated disc/drum valve would come on before the proportioning rate would, on an integrated disc/drum brake valve for a truck.
If you're gathering brake parts/components from a Dentside truck, it's better to stick with like series --get the brake parts from a Dentside F100/F150 if you are putting them on a Bumpside F100. The Bumpsides of like series and size with a Dentside donor of like series and size will be close to the correct weight the valves are designed to work with. A Dentside F250/F350 will have a slightly different proportioning calibration for a heavier truck.
Most MCs for F100 Bumpside and Dentside trucks, manual or power brakes, will have a 1.00" bore diameter. Some of the F250 and F350 trucks with dual diaphragm boosters had MCs with a 1-1/4" bore diameter. The larger the MC bore diameter, the more volume of fluid it will displace but, it will generate less pressure output than a smaller MC bore diameter. A large bore diameter will also have a very stiff pedal and you may find that it's difficult to get the truck to stop within a reasonable distance, if trying to use a large MC bore diameter with just a single diaphragm brake booster.
If the MC bore diameter is greater than 1.00", you would be much better off to have a dual diaphragm booster rather than a single diaphragm.
Brake engineers design the collective brake components to operate together as a system for a specific vehicle application. However, when you break the various components down, the MC is just a manually-operated hydraulic pump. It doesn't know what type of brakes you have. A given bore diameter is going to generate a given amount of output pressure, dependent on how much force you apply to the brake pedal.
A brake booster also doesn't know what type of brakes you have on the vehicle. In simple terms, it's just a force multiplier. It's going to multiply the output force, relative to how much force you put on the brake pedal. It takes a lesser input force (compared to what it would take with manual brakes) and multiplies the output force being applied to the brakes.
