I drive a 2002 F-150, extended cab, 4.2 V-6, 5 speed manual. Currently it has 108,000 miles.

Approximately 1 1/2 years ago my clutch started acting up. The pedal was spongy. On the way to work one morning the clutch pedal gave out completely. On that particular morning there was ice and snow on the ground, the ambient temperature was zero, and the windchill was -15 degrees. The tow truck driver was in a bad mood and I was pissed off.

I had my truck towed to my mechanic who I've used for many years for various vehicles. He's honest, and I can trust him (shocking I know).

My mechanic checked the master clutch cylinder and it was fine. He told me that the problem was, more than likely, a defective slave cylinder. And, guess where that is located? Anyway, being that my truck had 90k miles on it, at that time, I just told my mechanic to replace the entire clutch assembly.

He did as instructed. When I picked up the truck he told me that the clutch assembly definitely had some wear on it. One of the springs were broken. But, for a clutch that had been engaged/disengaged a gazillion times the assembly was in remarkably good shape (score one for Ford).

The slave cylinder had busted apart. Probably due to the extreme cold temperatures. And, that's what caused my original problem.

Okay, I said all that to say this: The clutch is acting up again. It's not as bad as before. But, I can tell that something isn't right.

On some days the clutch pedal is just as solid and tight as can be. There is absolutely no "play" at the top pedal position. It feels strong.

Then, on other days, there is a 1 to 1 1/2 inch of play in the pedal travel from the top position. I don't feel the clutch actually engaging/disengaging until the pedal has been pressed, or released, about halfway.

I can pump up the clutch and it will feel solid again for a little while. That "little while" could be until later that afternoon or a couple of days later. It doesn't seem to be affected by the temperature this time since this can occur when it's below freezing or when the temps are 80 degrees.

Well, here's the "kicker". The clutch pedal will only pump up nice and solid if I have the brake pedal pushed down. With my right foot pushing on the brake pedal, and my left pumping the clutch pedal a few times, I can actually feel the brake pedal pressure change.

I have always been under the impression that the clutch, and brake, systems are independant of each other.

So, my question is this: On a 2002 F-150, 5 speed manual, is there a point where the clutch, and brake, systems are connected in some way?

What else would cause this strange phenomenon?