Your manual does talk about the clutch/brake adjustment procedure. But - from what you describe - if nothing else get the Sears repair guy to come out and fix it or take the tractor to a good repair shop. It sounds as if some linkage springs or such have either broke or have been lost. Perhaps someone else that is familiar with the brand/model of your machine can give you better help.

I had that problem with an old Murray here. I got it from my Bro-in-law, then gave it to my son, who gave it back 5 years later, saying the tranny won't shift and the handle came off. So, out came the tranny, i took out the broken handle bolt, fixed it right, reinstalled the tranny, started it up, and went to mow. Tried to stop it, and it wouldn't stop, stayed in gear, i could not find neutral, and cutch didn't have any effect! Well, the engine now reposes in another tractor, and the rest is in line for the junk yard! Its a shame, because the body parts and tires are really good, but---alas and alack--its time!

This problem may require the services of an expert. Erratic brakes and a stumbling engine are ingredients that can lead to an accident. I'm no expert in this arena, but here are my thoughts. On startup, you are missing the vacuum boost to the brake system, and somehow, later on, some or all of the boost is regained. The engine stunbles consistent with a vaccum leak. You've checked for vacuum leaks, but may have missed the "big" one, the vacuum boost unit itself, or the vacuum accumulator and associated vacuum lines. At this juncture, I suspect that the vacuum boost unit of the power brake assembly has failed, and admits an overload of air to the intake manifold (when the brake pedal is depressed) causing the fuel mixture to lean out. Often associated with the vacuum booster is a small vacuum tank called the 'accumulator'. It will be attached to the vaccum lines that supply the vacuum booster. It's purpose is to have at ready a goodly supply of vacuum volume to handle a suddent demand, and to keep the heater controls happy during this step demand. This tank is very important if the the vacuum fitting on the manifold is 'ported', that is, has a orifice within it to restrict the amount of air flow in case of total vacuum system failure. This tank may have a one way valve. This is the vaccum source that aids one more application of the brake after the engine dies. This tank may be made of two plastic halves and ultrasonically welded together. A leak along this seam is possible. Do you have a hand pumped vacuum tester with vacuum gauge? If you do, remove the vacuum line that feeds the vacuum booster and apply vacuum directly to the booster. Pump down to a vacuum level, say, 10 psi, and hold. Can the booster hold vacuum or does it leak down fast. If it can not hold vacuum, it is leaking. You may have to block the brake pedal down past the valving point for this test. There is a valve in the booster unit that applies vacuum when the brake pedal is depressed, and it relieves vacuum when the brake pedal is let up. This valve can be a problem source.

I have encountered this problem on many vehicles in the shop i work at and it might be normal for a brake pedal to travel quite a bit when your are at idle in park. However, you would never press the pedal that hard or as far down when driving. You would end up through the windshield for sure. In my experience your particular vehicle has this weird feeling pedal travel when you are idling in park but the brakes perform as they should when driving. Air in the hydraulic system would cause a spongy feeling not a fading pedal, so bleeding is not likely to fix the problem. if there is in fact a failure in the system I would be checking to see if the ABS module is bypassing fluid pressure by blocking off the master cyl. if the pedal is high and firm( no travel) I would then block off the flex hoses and check for pedal height and drop. if this is ok un-block one flex hose at a time and see how much drop if there is a substantial drop at a certain wheel I would verify the hydraulic circuit to that wheel. first by bleeding to see if there is any air. Then I would put my attention to the hydraulic unit. Though I am confident that this is how these vehicles are and you don't have anything to be concerned about. Hope it works out