Hello, I'm a newer technician. I've been tuning for awhile but I'm still learning how to do a lot of repairs. I've been having a problem with my own 1947 Acrosonic piano and can't seem to figure out what to do.

In the lower range, the hammer rail falls down so the hammers can't rest on it. The rest of the hammers on the piano rest on the rail. When playing a note in the low range, the hammer will fall below where it normally rests on the rail and then is unable to make it back up when trying to repeat the note. Years ago, I hired a technician to fix it. He tightened the una chorda pedal dowel to raise the hammer rest rail so the hammers fell back on it. This only worked temporarily though. It seems to fall down after time. It also seems that it needs to be raised so high that it affects the sound and play as if you were to have the una chorda pedal down half way at all times. This is because the rest of the rail is fine.

Last year, I learned how to re-pin jacks and hammer butts. I had repaired pianos that seemed to have the same problem as mine, as far as the hammers not going up, by either re-pinning or just stretching out the jack spring and adding some Protek to the jack flange. On my Acrosonic, the hammers all fall fine. I took the action out and the jacks all seem fine. I tried stretching the springs and adding protek just in case it helped but it made no difference. The problem seems to be the hammer rail dipping down too much on the lower end and I can't figure out what to do about it.

Here's a picture if that helps

I also have another problem now. After I took the action out and put it back in, some of the dampers throughout the low and midrange aren't working. They all seem fine but just don't go down enough to mute the strings. I took the action out again just to look and see if I could see anything wrong. I couldn't and put it back in. Now more dampers aren't working but some that weren't working before are working better. I've experienced this problem before with other pianos and the problem was always that the action wasn't tight enough in. I've got this in as tight as I can though. Is there something I might be overlooking or a trick to getting the action in any tighter in these pianos?

Any advice will be very much appreciated. Thank you.

I'm very interested in what techniques people have for eliminating the bleeding dampers effect after replacing an old action. Sometimes I have been unable to figure it out.
One thing you can try is tapping the base of the brackets where it sits on the bolts underneath the action. This might help move the action in a better place for it to be tightened even more.

Seems like just some extra hard felt is needed under the hammer rest rail to hold it up so it does not completely rely on the soft pedal for support.

Also, the rubber grommet (if there is one) might be keeping the pedal dowel from seating properly.

It is important to have the proper hammer blow: 1-5/8" for spinets 38-30", 1-3/4", for 42-45" pianos. Adjust the hammer rail to give the proper distance. Key height is 2-1/2" with the sharps 1/2" above.

Taking out lost motion may make the dampers raise too soon, before they have seated on the strings. They should raise when the hammer is about 5/8" from the string. If you can make a spoon bender work, especially on a spinet, you are a better man than I am. I adjust them by holding the damper lever as I press the key hard, until it bends the spoon to the proper position.

There is a similar trick for backchecks. They tend to check too close to the string. Bend them back, then hold the wippen down as you bend the backcheck to the catcher. That usually will make the hammers check at about the proper 5/8".

Hah, yes. I have two types of "spoon bender" tool, and I've never mastered either of them. I saw Don Mannino demonstrate the "flat L-shaped" type beautifully at MARC in 2011, but I've not persevered enough to acquire the skill.

I like the holding-the-damper-lever method to adjust for dampers lifing too soon; must bear that in mind. Do you have a secret method for dampers lifing too late?

Matt, it's really hard to tell from the photo what's going on. It almost looks like the hammer rail is either broken or severely warped. It's possible the hammer rail has become detached on the bass side, or whatever it is that holds it in place on the bass side is bent/broken.

As far as getting the action back in ... make sure the bottom of each action bracket sits properly on its little post. If everything looks like it's in the proper place, it's possible the top of the brackets aren't seated properly in their places. Before tightening the screws, I take a fat slotted screwdriver, placed squarely against the top of the action bracket, and bump the screwdriver with the palm of my hand. If any of the action brackets weren't back far enough, you'll hear them pop into place.

It's also possible the case is coming apart at the keybed. I ran across this once, and some of the symptoms are similar to yours.

The hammer rest rail in an upright piano pivots on three or bent steel rods (or castings) that slide into the action bracket. If one of these is improperly bent or missing, it may cause the rest rail to be in the wrong position.

In a decently regulated piano (which excludes some that came out of the factory doors in the mid-twentieth century) there should be some key motion before the damper starts to lift. On the dampers that won't seat, check both notes that are behaving and notes that are not to see what you have for key travel before damper movement. If you do have this pre-lift key travel, spoon adjustment isn't your first move.

Yes, bend the spoons so they lift too soon, and then use the method for that!

Of course!

I agree that a broken hammer rail pivot or pivot bushing could be a likely problem.

But the first thing to determine is if you have the action seated properly. If the pedal rods are in place they can stop you from "feeling" when the action is properly seated.

Do not do any regulating until the action is properly seated. Because what you will be doing is de-regulating!

Thanks everyone for the advice. I'll give these things a try.