Toilets, Sinks, Showers, Tubs and Disposals - Possesed Shower! Please Help!!

My name is Kevin and I just bought a remodeled house in Washington. I'm going through the phaze now where you start to discover all the "little" things that go on your list of things to do. One major poblem right now is the shower. It's got one of the three handle spigots, you know hot, cold, and shower. When I turn on the hot or cold for the tub, it works fine. Most of the time when you turn on the shower it works, for a while. Just about the time when you get all soaped up, there is a "thud" and the water stops. I can turn the shower off and the tub faucett works fine, but the shower won't turn on. After a few minutes, you can turn the shower back on, but it'll only last a couple minutes. Not even enough time to get the temp right. I looked under my house and I have three types of water pipes, The flexible type, copper, and galvanized. The galvanized goes to the shower, but it doesn't look like there is to much corosion. I took my Nitrogen tank from my work and tryed blowing out any debris in the line. Any help would be appreciated. I would prefer to do this fix myself to avoid sevice call costs. Thanks

Kevin: Welcome to the forums. The vertical galvanized pipes probably won't have much corrosion in them. I believe you have a problem with the washer on the end of the diverter. Pull the diverter out and replace the cartridge or the washer. Post back with the results of your investigation.

Thanks for the welcom and the advice. It'll probably be this weekend before I take that on being as I'll have to romove the shower shroud. I started down that path the other night after reading a article on this sight. I got the first nut and a couple of washers out of the inside of the valve and ended up with a leaky valve. When I went to True Value to get some new ones I noticed the same looking valve as what I just took apart. What you just sugested was going to going to be my next guess. But again I'll have to remove the shroud to get to it. If you know of a way to easily remove it without damaging it or even to remove the valve and leave the shroud, My wife would be VERRY appeciative. :) Thanks again!
-Kevin

It's been a while since I origionally posted this, but I fiannly got it fixed. I got a tool that looks like a big spark plug wrench. I've heard it called a valve pull in these forums. I got the whole diverter assembly out and found a destroyed gaskett and a lose screw that moved the plunger in and out turning on the water to the shower. I worked that out and put the screw back into the end of the diverter and reinstalled everything. Now it works fine. All it cost me was the tool which was like $3 and a package of gaskets for $.83. Hope this helps somone in the future.
-Kevin