Had ongoing thread, re: brakes fading after steep climb & release accel. Pedal.

Do you mean the pedal gets hard to press? That isn't brake fade; that's loss of power assist. When accelerating or under load, engine vacuum goes way down so there is a check valve in the rubber hose going to the power booster. The booster will hold enough vacuum for two or three pedal applications. To test it for leaking, let the engine idle and check that the power assist is there. Next, stop the engine, wait five to ten seconds, then press the pedal a few times. It should be easy to press at least twice. If it's already hard, the check valve or booster are leaking. Use a hose pinch-off pliers while the engine is idling, then try it again. If you get two power assisted pedal applications now, the check valve is leaking.

Sorry, I'm not following your description. The brake pedal goes to the floor? The brake pedal is hard while accelerating, then there's no resistance and it goes to the floor after you release the gas pedal? How are the brakes during normal, slow driving? Is the brake pedal firm and high or does it go too far to the floor?

"No brakes" can mean different things but if the pedal is hard to push, that's a loss of vacuum. If the pedal goes to the floor, I'd suspect the brake fluid level is low. You might try looking for a kink in the vacuum hose going to the power booster. Perhaps it gets restricted when the engine rocks from pulling up a hill.

There should be a low fluid warning light but even if that isn't working, if you look at the design of how the reservoir feeds the two sections of the master cylinder, there is enough above the pistons that going up a steep hill shouldn't matter. If the fluid is that low, you should have the same symptoms all the time, not just on a hill.

I'm trying to think of other common causes. What exactly is the symptom when you say "no brakes"?

I'm still thinking about it and can't offer any suggestions if the reservoir is full. There are two independent hydraulic circuits and to lose braking in both of them is very unusual under any circumstances, let alone such a repeatable one. There can't be air in the system because you'd have a low and mushy pedal all the time.

What you might try is holding pressure on the brake pedal for half a minute to see if it slowly sinks to the floor. With no external leaks and no loss of fluid, a sinking pedal is due to internal leakage inside the master cylinder. A trick to get an intermittent internal leak to show up is to vary the pedal pressure with your foot but never totally release it. Often the higher foot pressure will put more outward pressure on the lip seals causing them to seal better. Since you want a leak to show up, reducing the pedal pressure intermittently can allow the lip seals to relax to where they let fluid sneak past them.

If the pedal starts to sink, replace the master cylinder. It would be very odd that you haven't noticed a loss of pedal at any other time if it's due to the master cylinder, but obviously we're looking for something unusual.