You have to analyze the whole system, like the relationship between the key dip and blow distance. If the pedal doesn't move down far enough, there won't be enough movement/travel of the rail.
See if the linkage to the pedal is in the same hole as when it was new. If the pedal was replaced at some point, maybe they connected the linkage to a hole closer to the pedal pivot, and that would limit how far the linkage moves when you press the pedal.
Some Yamahas have different lengths of their side brackets, and they put the pedal linkage connection closer to the pivot point, which allows the rail to travel farther down for a given "pedal dip". More angular motion with the attachment point closer to the pivot. Try to find a way to move the linkage wire attachment point closer to the pivot so it will move farther. Most Yamahas are pretty good and the mute rail usually has plenty of movement up and down. Something is amiss.
Also, look at the attachment of the mute rail to the left side bracket. Make sure that they fit together as designed and are not tightened at an angle. You may want to remove the rail and tighten all the bracket screws to the rail. There is usually a small hole in the bracket and corresponding "pin" in the rail that keep the rail and the bracket in the proper position when you tighten the screw.
Look at the attachment to the linkage where it connects to the bracket. Is it bent somehow so that it limits the travel of the rail?
Are there extra holes where the pivots attach to the inside of the case? Perhaps someone drilled new ones in an attempt to correct the situation, then later someone put it back in the old holes. You get my drift.
Look at everything in the linkage to see if something wore out, broke off, got loose, etc. Also, check the spring that lifts the rail. If it's too weak, it won't hold up the rail properly when it's in the "off" position. You might have to drill a new hole for the screw-eye to increase the spring tension.
Has the felt been trimmed excessively? Has it been replaced?
Is there some felt block glued under the pedal to keep it from making a metallic noise that might be limiting the pedal movement? Is the pedal bracket loose? All sorts of things can happen in an old piano that are not immediately obvious to cause problems like this. A spring under the pedal that helps lift it might be broken and you can't see it because it's hidden under the pedal.
I've had to advise the client that I can't fix or adjust it, so they might just get used to not using it. Aka, I give up!
Paul McCloud, RPT
Accutone Piano Servicewww.AccutonePianoService.email@example.com
Sent: 12-06-2022 00:56
From: Scott Cole
Subject: U1 practice mute issues
I've adjusted many practice mute systems, but I ran into one today that stumped me. It's a 1980 U1.
The customer reported a key was stuck down, and I saw some hammers were getting stuck on the mute felt.
Easy, right? Just crank up the turnbuckle enough so the felt clears the hammers? Nope.
When I had the felt just clearing the hammers, two things would happen:
1. The mute felt now wouldn't go low enough to have any effect and
2. The turnbuckle rods were getting so loose I was afraid the whole thing would start to rattle under normal playing.
A little trimming of felt or some adjustment has always did the trick, but something else is wrong here. I'm just not sure what.
Anyone else had problems getting these adjusted just right? I've worked on a bazillion of these things and never had a problem.
Scott Cole, RPT