The story: replaced brake master a year ago. Everything working great. Brakes like any other car I've owned.
Replaced the Toyota drum axle with a drum brake ford 8.8 (so different manufacturer brake system in back, but same type of system) installed SS lines in front and back. Completely rebuilt the rear drums with all new ford parts, including slaves. Bled brakes with DOT4. Go for a drive. Pedal feels stiff when gently depressed. But immediately gets soft and travels a bit before hardening back up and applying full force to all four brakes. So I re bled the brakes. Found nothing unusual, and got no change.
My thoughts: either I have a bad master. (already? It's bendix.) I have a bad proportioning valve. Or my stock master does not play well with the hydraulic system of the ford brakes.
What do you guys have? The booster wouldn't do that right?
Sounds like your booster happened to go out while you were changing other components, but it's worth checking the other stuff first. What was the bore size on your old wheel cylinders? And the new ones? Did you leave the rear restrictor in place or change it to the Ford one?
I kept the ford restrictor in back and just used adapter for the m10 to 3/8 lines.
My wagon had a similiar issue after new lines. It would stop with gentle pedal pressure but hard pressure it felt like they engaged, failed then re engaged. On gravel it was actually locking up the rear tires on initial pedal then the dead spot and fronts finally worked.
Mine turned out to be a bad prop valve. Cleaned the front brake circut to no avail but cant get into the rear circut. The check valve was stuck in rear bias from when the front line blew.
You can try tapping the prop valve while someone slowly applys brake pressure. This has been known too free them.
In reply to dropstep:
Cool! Will try this and report back!!!
Did you take the Toyota restrictor out?
If yes, then clean out the Ford one per dropstep.
The Toyota restrictor is in the master. I actually had to buy a used one from a forum member because when I replaced my master the new didn't come with the restrictor fitting. Maybe it's because I have two restrictors! One in the master, and one on the axle. That's what the tee fitting in the ford axle does right? Besides split the lines?
Actually, looking at it, I don't think it is a restrictor.
The rear tee is just a splitter not a restrictor. Ford uses the prop valve just below the master for a restrictor.
You can check your booster by engine off, pump brake pedal 4-5 times to deplete vacuum reservoir or until pedal has no assist, while holding brake pedal down start engine. Pedal should drop if booster is operating properly. I assume you have the rear brakes adjusted properly. Are the rear slaves the same piston diameter as the toyota slaves? If they are larger, they will require more fluid to activate the rear brakes. Thus more pedal travel before a firm brake pedal.
They are bigger than the yota slaves. So that's a good point. Perhaps an adjustable proportion valve is in the future?
I wonder if removing the restrictor in the yota master would allow more pressure to get back there sooner? I know the gts model of Celica had discs in the rear and that's the reason you don't get the right fitting when you buy a new master. (Guess parts suppliers only figured the gts would be around after so many years.
The proportioning valve limits full pressure to the rear brakes in panic stop situations. It will not solve pedal travel concerns. A larger volume master cylinder/smaller slave cylinders will. (this was addressed on another thread not long ago (1-2 weeks)
Doh! Totally fixed my brake issue. Adjusted shoes and not no more slop! Thanks so much guys!
