Help me stop - brake question

68 - 302 auto with power disc front and drums rear. I can bottom the petal out on the floor and the car will stop, but not strong enough for a panic stop or lock up any tires.

I’m looking for assistance/suggestions on what to check next. Here is what I have done so far:

Rebuilt factory power booster with good vacuum. New master, bench bled. Rebuilt factory proportioning value. New rubber brake lines. New rear cylinders. All lines have been bled numerous times in the correct order. Plenty of life on all pads and shoes.

If the rears are not adjusted to rubbing enough, would that cause this? Would better front pads help?

Front brake calipers replaced? Are they right side up?, if not, they will not bleed all the air out. The bleeder should point horizontal, not up.

Like Mike says - the typical scenario is swapped front calipers because the technician points the bleeders up instead of aft.

Check if your new master cylinder is proper style and piston bore diameter for disk front drum rear. It may be a drum front drum rear master and distribution / proportioning valve set up. Was the car originally equipped with disk front, or did it get modified to disk front? It needs to have the proper brake pedal setup. Did your rebuilt factory power booster have the straight eye design pedal push rod attachment or the tear drop style pedal attachment. The adjustment measurement of the booster push rod into the master cylinder may be wrong also, which won’t allow the proper engagement of the rear brakes and cause pedal to the floor.

Some great questions, thank you. Let me help clarify my setup. The car is a factory power disc car and drum rear. I replaced the master cylinder with one from West Coast Classic Cougars that is meant for disc fronts. It has a 1" bore.
The proportioning valve on the car is original, I took it off last year and cleaned it out and used a rebuild kit for it. The brake booster is the original as well and was sent to Booster Steve for the rebuild. I will have to crawl under the dash to check on the linkage, but I believe it is the tear drop style. Where can I find out about the measurement of the booster push rod into the master cylinder?

Likely swapped calipers.

Great idea about the calipers, but I checked tonight and it appears that the bleeders are horizontal. If my bake brakes are not adjusted properly (shoes too far away from the drums) would what I am experiencing be a symptom?

Yes that will definitely cause it too. The shoes should just drag on the drums when they are rotated.

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Did your brake system work appropriately but just needing a rebuild before all of the parts rebuilding and replacement ?

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Good question. The booster was shot when I bought the car and so were the rear cylinders. I replaced the rubber lines and rebuilt the proportioning valve as part of the refurbishing of the car. The plan was to make the brakes better. Ha.

I had a similar issue with my 69’. I ended up replacing the entire booster/reservoir system. Brake Fluid got into the original booster and over time just made it not work so well. Booster was still solid, with the diaphram intact, but soggy brakes with no assist. Tried first replacing the reservoir, but noticed the seal leak. You should be able to check through your vacuum hose or between the reservoir and booster. If you see moisture of brake fluid its likely time to swap. There may be a better solution, but thats what I ended up doing.

There is a rubber cushion that always or almost always falls off the master cylinder plunger if the plunger is removed…I’ve seen it several times…many times the cushion falls inside the booster. Replacing the booster will fix it but trying to find the cushion if it’s fallen inside the booster and reattaching it will be the easiest

The booster was removed after I took ownership of the car. I sent it to Booster Dewey to have it rebuilt. I do not remember the status of the cushion when I reassembled everything. My current plan to re-adjust the rear shoes and test. If that does not help, my next step will be to pull the master cylinder, check the plunger and measure it as well.

I had a similar problem and the cause was the rear brakes. I had adjusted them so they dragged a little when the wheel was rotated. This was not nearly enough. I ended up taking the car to a shop that specialized in old cars and they readjusted the rears and the problems went away,

Update: I did adjust the rear brakes some more to the point there was definitely drag. It helped a bit and the car stopped harder, albeit with the pedal to the floor. I still feel like there is a lot of travel in the pedal before the brakes actually engage. My next step will be to pull the master and measure the rod to make sure it’s in spec. I might even toss on a set of new front pads.

Any update on this? Having pretty much the same issue. Pedal to the floor gives me decent stopping, but definitely will not lock up the tires. I’m wondering if the WCCC rebuilt booster/master cylinder would fix my issue. I just bought Porterfield R4S pads for front and shoes for the rear drums, so I’ll see how much difference that makes.

My Pedal also goes deep, I shortened the “back throw” by lowering the brake light switch…so I didn’t have to lift the hoof as far, but I think that didn’t allow the drums on the rear to release properly… so I have just backed the brake switch back out for that high lift feeling.

In my experience old Ford brakes (late seventies Oz XC Falcon through EA Falcon anyway) always felt dodgy compared to Holdens (Oz Chev) and Valiants (Oz Chrysler)… High and sloppy with a funny stiction point in the pedal before the pedal actually grabs … once on they work good especially with bigger rotors… until they fade due to the car being 120% bigger or heavier than the other two.

Of course after writing all that, it occurs to me that the reason my Cougar’s brakes feel like 70’s Falcon brakes…. Is because it has 70’s Falcon Brakes…. And yours don’t… uppercut to self…

Update: Was busy chasing what I thought was a dead valve on #8. Turns out my 2-year-old rebuilt brake booster had a massive vacuum leak and was not doing anything. In order for me to get the car back on the road quicker, I bought a MBM brakes Midland booster and just installed it this past weekend.

I also put on new front pad and rebled the entire system. The pedal does go to the floor still, but now, while driving if I quickly press the pedal, I can lock up some of the tires and the car does stop quicker. I feel safe driving now, but wish the brakes engaged a little earlier in the pedal throw.