I have a 1969 F250 Ranger CS. Truck runs and drives fantastic however, the brakes hardly work and when they do only the rear wheels will lock up unless I slam on the pedal as hard as I can. I know drum brakes front and back are gonna suck, but they shouldn't suck this badly.

To try and fix this issue I have:
-Replaced the Booster and M/C (twice)
-Ran new brake lines
-Replaced the shoes and wheel cylinders
-Bled the brakes more times than I can count (including gravity bleeding)
-Adjusted the shoes
-Prayed to God
-Cried

What I haven't done:
-Sell the truck
-Replace the distribution block.


I'm at a loss. Maybe I installed the incorrect size wheel cylinders. If anyone has had an issue similar or has any idea what else I can try that I haven't, help would be greatly appreciated.

 

Is the plunger adj properly on the booster to master cylinder? There is a specific length the little plunger is suppose to stick out. Did you adj the shoes so they drag just a little, or free spin. Was the shoes ground to fit the drums?

Now a plugged or restricted proportioning valve can cause some brake weird problems like some of the ones. Like indicating a bad MC.

 

My first thought is the shoes still need some adjustment.

When you adjusted the brake shoes did you run the shoes all the way out until they made solid contact with the drum and you could no longer turn the drum? Doing so centers the shoes inside the drum.

After centering the shoes, back off the adjustment until you can turn drums by hand and hear the shoes barely brushing against the drum.

Another thought since you said you're getting rear brakes but not good braking up front is your combination or metering valve is not centered so most of the fluid is going to rear brakes when you press the pedal. I'll provide some instructions from a later model truck on how to center that valve below (I think the process would be the same for yours). If that doesn't do the trick you might need to disassemble that valve and clean it so the metering valve can slide back and forth as intended.

Did you replace rubber brake hoses and all the the steel lines? Could be some internal corrosion or one of the steel lines was crushed at some point restricting flow.

 

Yes the first time i replaced the MC I set it up exactly as it was on the old one. The second time, I extended it out as far as it would go. Both acted the same way. No brakes till end of travel.

I've adjusted the shoes several times. And I've even adjusted them out far enough to where the the wheel will hardly spin. I didn't grind the shoes down but I had the drums turned.

As for the proportioning valve, I haven't found anything on the truck that resembles one. Apart from the distributor block.

 

For the shoes, yes, I adjusted them like you said.

I've been messing around with the truck all day, and I noticed that it's ONLY the rear driver side wheel that locks up when braking unless I slam on the brakes as hard as I can. And what little braking I have isn't much. As I mentioned in my original post, it's only until roughly the last quarter of travel that the brakes do anything. There is also little to no resistance in the pedal. I wouldn't even call it soft; it feels like it isn't there. Now, while the truck is off the brake pedal will firm up and feel normal; however, once the truck is running, it immediately goes soft.

As for the Combination/Metering/Proportioning valve, I haven't seen anything in this truck that resembles one. The closest thing I've found is the distribution block, where the two lines from the M/C run in, and it splits into two going up front and one going to the back. (see attached image)

And yes, apart from the lines going from the dis block to the M/C, I've replaced the lines, including the rubber ones. And yes, I know they look grimy in the photo, but between living in the Rust Belt and having messed with the entire brake system, they've seen better days. I also reused the fittings.

 

Did this truck have power brakes originally?

Looking at the booster and MC from below they look to be from a later model vehicle. It's interesting the the pedal feels normal with engine off, but when running it gets spongy. Makes me think it might be related to the brake booster and/or MC. If that MC came from a donor that had disc brakes, there could be issues using it with 4 wheel drum setup.

You mentioned you haven't replace the lines between MC and distribution block. Might try disconnecting those at both ends and blowing some compressed air through to make sure there is no obstruction. Are there any kinks or dents in the lines between MC and the distribution block? (you're right that doesn't look like any factory combo valve I have seen, but I am more familiar with the 73-79 trucks).

 

Well, that's why I've replaced the Booster and M/C twice now. When I bought the truck originally (back in 2022), it did have power brakes. Now, whether the previous owner converted to power brakes, I don't know, but the Booster and M/C looked about as old and rusty as everything else. The brakes were okay. Better than they are now. But everything started to leak, so I replaced them. I just went to Autozone and bought what they had. Then the brake issues began.

Upon researching, it appears that Ford offered both Drum/Drum and Disk/Drum setups at the same time, and that the Booster and M/Cs were different depending on which you had. So that's why I replaced them a second time. And made sure they were for Drum/Drum setups. Both times I've replaced them, they've been remans. But the second time, I purchased them from Rock Auto since the listings specify which application they are meant for

 

Since the brake sensor for the proportioning valve is not connected, it may be stuck in a position that not sending the fluid to the front. Put a ohm meter across the pins and see if it's tripped, shorted. The proportioning valves are different for drum/drum vs disk/drum vs disk/disk.

 

If your rear wheels are locking up first, your brake lines are probably reversed on the master cylinder. I had bought my 1970 F100 from a very smart mechanic and the rear brakes would keep looking up under hard braking, found out the lines at master cylinder with switched, so the rear brakes were getting a majority of the braking force. Even the best of us make simply mistakes.

 

The part pictured in posts 5 and 8 is not a metering valve, it is the brake pressure differential valve. There is a sliding block inside that is intended to close off one end of the brake hydraulics if there is a system leak. When that happens the slider grounds the wire that runs from the center mounted switch to the brake system warning light (it looks like that wire isn't there in the pic) next to your parking brake release handle, turning on the red light to warn you that there is a brake system leak. If that slider got moved to one side (which can easily happen if it is not pinned with a special tool when bleeding the system) it can affect the front-to-back distribution of the brake hydraulics.

 

I have found this article helpful for my 67 F100, manual drums all around.

Proportioning Valves 101 - FORDification.com

 

Sounds to me like this ^^^^^^^ right here, as I ran into this myself about 3 years ago when we moved.

 

My answers to this are always the same:

1. The pedal being hard when the engine is off and soft when the engine is on, is absolutely the normal working of a vacuum booster.
This is showing, at least for now, that the booster seems to be functioning properly.

2. A simple test you can perform, at least to see if the rear brakes are adjusted properly, is to apply the parking brake one or two notches and see if the height of the pedal rises slightly when the engine is running.
It’s not a fix, but it’s another clue as to what might be going on.

Also, applying the parking brake fully (just sitting, not driving), tells you immediately whether the brakes are adjusted close to correct. Engine running or not.

3. Revisit the adjustment procedure between the booster and master.
Booster rods are adjustable for a reason. and some master cylinders come with an additional “bullet” that gets inserted to make it power brake compatible.
Even back in the 60s and 70s there were slight inconsistencies in manufacturers. Nowadays, it’s ubiquitous. Rampantly crappy even!
Some masters and boosters are now completely incompatible. It’s just up to the installer to determine that.

So my suggestion, after the first two, is to separate the master and booster (you shouldn’t even have to disconnect the lines) and adjust the rod out further. Just a random amount like a quarter inch.
Slide the master back to the booster and see if the rod touches down on the piston before the master meets up to the booster flange.
If not, adjust it out further.
if it does, then adjust the rod back in enough so that it just clears before the master and booster meet.
There is a proper way to measure this, of course, but in a pinch, and without the easy to use tools, this gets the job done.
You want the gap to be absolutely minimal. There is a specification on it, but I never remember what it is off the top of my head. Something like 1/64 of an inch or similar.

I know you’ve played with this multiple times, and changed the parts twice. But I would still verify the exact gap between the rod and master.
Just to be sure that this is not the majority of your issue.

 

Sorry to resurrect an old thread... it's only been a year, but after much research I have found this to be WRONG! No offense, but this "brake pressure differential valve" is just an electrical switch to let you know that either the front or rear has lost pressure. Even when it is all the way to one side, it does not restrict the flow of fluid to either side, and centering it after repairing the brakes only turns the light off. The protection from total brake loss comes from having a dual reservoir MC, not this "valve."

PLEASE someone let me know if I am wrong. I have been chasing down the exact problem the OP posted about... rear drivers side locks up first.

 

If one side is locking before the other back off the adj on the one locking up. Now if the wheel cylinders have been replaced it's possible one of them has a different size cylinder. In would also check for a kinked or damaged line at the rear housing.