If there is only one PRV in the MC, it sounds like you have the wrong one. If it is a DISC/DRUM MC, it will not perform correctly regardless if you add an outside PRV.

 

FWIW the MC I got is the correct part number and looks the same as other Drum/Drum MC's for a '67 fairlane.

 

Can you get a picture of the ports?

In my experience, disc/drum MC's usually have a different sized pistons for the drums and the discs. The pictures appear to show a single diameter, which would mean drum/drum.

 

I finally found a RAYBESTOS APPLICATION CHART and that PN is correct for a 1967 FAIRLANE MANUAL DRUM BRAKES and supposedly has the valve(s). Who knows with the quality of today's parts?

Are you considering installing inline valve(s) also? You may run into complications there.

BTW - What year and model is your truck? You may have a mis-match in cylinder sizes.

 

Yes, I bought one valve and will buy another valve here soon--waiting for them to ship. One for each MC circuit.
What complications? I have a couple places I could easily use to put the residual valves in.


It is a '56 F100, the drums and wheel cylinders are stock, new hoses, all hard lines are replaced, and obviously the lines for the brake MD are all a custom "mess"...

 

You're correct. My HS REMEDIAL READING COURSES just cut in.

The FRONT OUTLET is for the rear brake system while the REAR OUTLET (closest to mounting flange) is for the front brake system.

The PDV (PRESSURE DIFFERENTIAL VALVE) is not actually needed but is a safety feature as all leaks may not result in an immediate failure but the valve and lamp should warn before a major failure. The split system is only meant to allow you to safely stop the vehicle with either front or rear circuit operational, not to keep driving to the package store.

 

OK, we have established the aftermarket MC has RESIDUAL PRESSURE VALVES in either port, so it is a DRUM/DRUM MC.

1) Was the new MC properly bench bled before install?

2) Which MC push-rod did you use and is it the correct length and/or adjusted correctly?

3) The brake shoes need to be adjusted tighter, especially if they do not conform to the drums circumference at first install (they need to be seated in or arc ground)

4) And you ain't gonna like this one but the FAIRLANE MC has a 1" bore whereas the stock MC has a 1 1/16" bore.

The truck system needs that MC size to properly operate the brake system correctly. A drum/drum system is balanced by shoe size(s), wheel cylinder size(s), and MC bore size and is particular to each vehicle individually. That is why there is no proportioning and/or metering valve(s) used.

Your MC is installed under the floor, correct?

 

1) yes it was(I actually installed it to the bracket then I bled it using two cut pieces of brake line spitting back into the two reservoirs)

2) I used the original push rod as it fit the bolt correctly; the supplied rod would have not grasped the bolt. It was adjusted for just a smidge of play.

3) brake shoes were adjusted to where they were almost difficult to install. If they did make a nice rubbing sounds whence installed, I adjusted them the hard way a bit more tight on the drum.

4) Yes I remember running into that but I basically just said "screw it" let's see what happens.
My issue has nothing to do with lack of braking power; it simply is acting like theirs air in the system when I'm 97% sure there isn't.

Yes it's installed under the floor.

 

Good point, I'm not sure this is the problem tho. The difference in area of the 1" pistons vs 1-1/16" is about 12%. I would think that pedal travel would be increased, but I'm not sure it would be so noticeable, or require a 2nd pump.

I'd add that my experience has been that rebuilt dual MC's have a 50-50 chance of being bad out of the box.

 

You also have to take into consideration the 67 F/L wheel cylinder size(s) (depending on model series) compared to the 56.. The 1" is meant to activate that system, not a 56 truck. This MC retro-fit is more for pre-67 MUST and such.

Well, the MC is supposed to be a new assembly, although most likely off-shore. RAYBESTOS is not the quality it once was. And MC integrity is supposed to be tested after install.

Guess and wait and see what happens. Two 10# PRV in series on one circuit should be interesting.

 

Fairlane wheel cylinders (4-wheel drum):
F - 1.125" bore
R - 0.9375" bore

56 F-100 wheel cylinders:
F - 1.0625" bore
R - 0.875" bore

Different, but not much. My money is on air in the system.

Not sure RPV's in series will make a difference, IF they have the same ratings.

 

Yes Ross and that's what I'm banking on: The OEM RPV's have a lower rating than 10psi. So adding my 10psi units to the front and rear circuits may help.

After about 2 months of sitting, the truck moved today and appears to run good--the radiators kept springing leaks from the same exact area, so I did an absolute hack job an making a '96 Ford Explorer radiator fit. I didn't hack the truck itself too bad, but the whole job would make most of you guys with actually nice trucks cringe. It would take a few weeks to kill each replacement radiator so now I'll just have to keep driving it and wait and see if this radiator springs a leak. (thread regarding my radiator issue https://www.ford-trucks.com/forums/1...-champion.html )


With that being said the brakes are the same, gotta be pumped but they stop the truck fine.Just as always. i drove that truck for a combined 3 years 7 days a week--hot or cold, rain and shine--with sorry *** brakes that had to be pumped. I can do it for another months while I slowly resolve this brake issue(hopefully).


Thanks all for the input, I really appreciate you folks actually delving into the subject and logically thinking it through. Best darn forum around.