Low Pressure at Shower/Tub Only

[cturboaddict]

I purchased a 1920s home last year that had alot of remodeling already done to it. Bathrooms/Kitchens have all been redone.

My kids rooms and bathroom are on the upper level of the house. Their shower/tub faucet/head water pressure is really really low. Every other item in the home including the upstairs toilet and sinks have good pressure. Just this shower/tub. It doesn't matter if it's it's pouring directly out of the spigot for the tub or the shower head. Both slow. Hot and Cold are both evenly slow. I'm not familiar with these exposed setups.

Now the tub itself looks to not have been swapped during the remodeling before we moved in. And the shower faucet/head is one of those exposed valve setups. (SEE PICTURES)
Shower2
Shower3
Shower1

I climbed into the crawl space and located the copper pipes, which look to be in great condition. There is a "T" right where the stub ups into the bathroom are (under the floor) that feed the sinks and toilet from the same line. There are no shutoff valves at the shower (only ones through the floor for the sinks/toilet). I've tracked the feed lines into the basement and find no shutoff valves there as well. Seeing that every other device that is hooked to these water lines has good pressure, I'm assuming it's got to be the valve/head assembly. So essentially there is a straight shot from cold and hot water to the upstairs shower.

Can anyone help point me in the right direction to track down why there isn't any pressure.
Can this valve assembly be disassembled by taking off the hot/cold levers and possibly refurbished for good pressure?

 

[cturboaddict]

Well, I shut off the water yesterday. And took out the valves.

Shower Valves

They seemed to function just fine, all the seals looked good. And there was minimal corrosion. I turned on the hot/cold lines to purge the exposed piping and the pressure was just as bad, barely spitting out. I looked into the two pipes that feed to the main intersection where the valves are and the path looked clear.

This leads me to assume that it's somewhere in the piping. Most likely behind the tub/wall.
What next?

 

[Sponsor]

 

[Jadnashua]

Do you get slightly discolored water when you turn the valves on after sitting for say overnight? If you do, it probably won't be for long. That would be a sign that there's some galvanized steel piping in there. When that ages, the rust buildup can almost literally shut the water flow down before it rusts through and starts to leak or fall apart. While not great, some people put steel drop-ear elbows verses copper or brass, or there could be a galvanized nipple in the path.

 

[cturboaddict]

I do not.