Power Brake booster and Disc conversion 1972

[guhfluh]

If you're converting a bump side truck over to dent side front disc brakes, the proportioning calibration of the factory disc/drum combination valve from the dent side will be pretty much ideal for the bump side (of the same truck series and size) since the bumps and dents are very similar in weight and size within their particular series.


http://www.stoptech.com/technical-suppo ... ing-valves

http://www.mbmbrakeboosters.com/index.p ... &Itemid=10

Agreed.

That first link is great and basically reiterates exactly how I feel about the situation.

The second link brings up a subject I haven't thought about in a long while - residual valves. Do our trucks use them? From what I've seen of cutaway drawings posted of the distribution block and master cyls, I don't remember seeing any. I have never experimented with them and don't know if one(or two if front drum) would be beneficial. Should aftermarket replacement MC's have them as well? Should you and I check to make sure our MC has one if needed? I currently have all drums and have felt as if more pedal travel is needed than should be required, after replacing my previous aftermarket reman MC with another aftermarket reman under warranty and they were obvious external build differences, one being port thread sizes, the other being a plugged hole on the bottom that isn't there on the new one.

[guhfluh]

http://www.fordification.com/tech/image ... Bendix.jpg

It does look like our stock master cyls should have residual valves built in. It still brings up the question of who has checked theirs to make sure their master does have one for the drum circuit and doesn't have one for the disc circuit? I believe I'd like to check mine, as I don't know that it has any. I also know people who have reused their drum master when changing to front disc's and wonder if their disc's are dragging excessively from it.

[ultraranger]

If you're converting a bump side truck over to dent side front disc brakes, the proportioning calibration of the factory disc/drum combination valve from the dent side will be pretty much ideal for the bump side (of the same truck series and size) since the bumps and dents are very similar in weight and size within their particular series.


http://www.stoptech.com/technical-suppo ... ing-valves

http://www.mbmbrakeboosters.com/index.p ... &Itemid=10

Agreed.

That first link is great and basically reiterates exactly how I feel about the situation.

The second link brings up a subject I haven't thought about in a long while - residual valves. Do our trucks use them? From what I've seen of cutaway drawings posted of the distribution block and master cyls, I don't remember seeing any. I have never experimented with them and don't know if one(or two if front drum) would be beneficial. Should aftermarket replacement MC's have them as well? Should you and I check to make sure our MC has one if needed? I currently have all drums and have felt as if more pedal travel is needed than should be required, after replacing my previous aftermarket reman MC with another aftermarket reman under warranty and they were obvious external build differences, one being port thread sizes, the other being a plugged hole on the bottom that isn't there on the new one.

In their OEM design, the Ford MC, for a bump or dent, would have had an RPV (Residual Pressure Valve) in the MC port(s) that were feeding drum brakes. However, today if you go to the parts store to get an OEM MC replacement for your vehicle, it's very unlikely it'll have an RPV installed in it, regardless if it did have them from the factory.

[ultraranger]

http://www.fordification.com/tech/image ... Bendix.jpg

It does look like our stock master cyls should have residual valves built in. It still brings up the question of who has checked theirs to make sure their master does have one for the drum circuit and doesn't have one for the disc circuit? I believe I'd like to check mine, as I don't know that it has any. I also know people who have reused their drum master when changing to front disc's and wonder if their disc's are dragging excessively from it.

The RPV is essentially a duck - billed check valve. Fluid easily exits from the MC towards the brakes but meets with some resistance returning to the MC once the pressure in the line reduces down to around 10 PSI.

Up until around the 1950s, MC'S were mounted under the floor board. This placed the MC at or below the level of the brake ' s wheel cylinders. Drain back was a problem with this setup where fluid in the wheel cylinders would drain back into the MC. With this drop of fluid level in the wheel cylinders, it would require the driver to pump the brakes to refill the wheel cylinders to get the proper reaction out of applying the brakes.

RPVs were installed to keep the wheel cylinders from draining down. By the 1960s, MCs were mounted high on the firewall and drain back wasn't much of a problem --although auto manufacturers still installed RPV in the circuits that were feeding drum brake components.

By the 1980s MOST Ford brake systems didn't have RPVs in the brake system. My '89 and '90 5.0L Mustang GT's (factory disc's front/drums rear) didn't come with an RPV in the rear brake circuit.

As I mentioned earlier, it's very rare to get an OEM MC replacement for our old trucks, from the parts stores today, with an RPV installed in it. If you just bought a new MC from the parts store and are holding it in your hand, it's pretty easy to check it for an RPV. --if it's on the truck, you would have to pull the lines loose from the ports to check.

If you take a small diameter drill bit that will fit through the small hole in the seat of the MC port, turn the bit around and carefully insert the shank end into the port. If the bit doesn't go in very far then an RPV is present. If the bit goes in a fair distance, then no RPV has been installed.