I have been looking everywhere for my specific problem, but haven't found anything. The sink and toilet in this bathroom work perfectly. My problem is with the tub. It is a one handle faucet, and cold water pressure is fine, but if you turn it to warm or hot, there is barely any water flow, and there is a shuddering sound from the pipes. If you turn the shower on, you are able to have hot water without the shuddering, but it is very low pressure. I really want to be able to take a nice hot bath this winter, but we don't have the money to pay a plumber to come in and fix this. Any ideas what this might be? I am pretty handy as long as I have instructions. Any help will be greatly appreciated.

What has happened is that some mineral build up in the pipe walls has broke loose and is now blocking the inlet ports of the valves cartridge,
Shut the water off ands open up the tub valve . Remove the cartridge and check and clean the inlet ports. While the valve's open place a pan over it and turn the hot water on to flush out the supply. You should have a full sream when you do this. If not let me know. Good luck, Tom