CAUT

I've dealt with several recalcitrant squeaky shift situations and here's what helped.

Scraping: On a crop of NY and Hamburg Steinways (from 2017), the key bed and key frame on the right side had a gunky substance looking like bee's wax. I had to scrape it off. Deep scraping, taking off the entire top layer of wood. Sanding wasn't enough. The surface should feel completely clean, free of any grease or waxy substance.

Soft wood: On many recent NY Steinways, there is no hardwood insert in the key frame where the shift iron contacts it. The iron creates a dent in the spruce and that will squeak. Further, someone had applied a greasy substance, and that exacerbated the squeak. I cleaned it with repeated applications of 91% alcohol, and then ended up scraping the surface. On several frames I had a hardwood insert installed. The endgrain should run toward the shift iron. I've had squeaks with maple inserts oriented front-back.

Lube: In all cases, when the key bed and frame and all metal contact points are clean, applying McLube444 (or 1725) and letting it dry thoroughly (15 minutes) will eliminate the squeak and the shift will feel totally smooth. 

Be sure to lubricate ALL contact points, which include the tip of the shift iron, return spring, and end pins on the front rail. Aside from the wood on and under the front, balance, and back rails, and the glides, I lubricate the glides' path on the key bed. That reduces the wear and makes it easier to slide the action in and out. And, it's nice to lubricate not only the right, but also the left key frame wall. That makes it slide against the key frame rest cleat, reducing the wear of the cleat cloth if you remove the action frequently.

I used to apply dry soap bar (Ivory soap) to the contact points and that worked well back when the soap bars were good. Recently, ivory soap has been soft and gunky, and doesn't work at all. I've used hotel soap bars as well in the past, and those worked, but repeated applications of soap lead to buildup that has to be eventually scraped off. The soap attracts dust and dirt to some extent, and becomes ineffective in high humidity, so I don't use it anymore.

In the picture there are black rub marks on and around the glide bolts. I would use alcohol to clean the frame and the bed really well. Removing whatever has been applied. 

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Was the keyset replaced as well as the keyframe?  The geometry of the contact point vis - a vis the shift lever could be at variance to the original keyframe. As others

have noted,  any loose glue joints could be suspect.

If  keybed was sanded was the proper hollow respected?

maybe the keybed or the keyframe is warped and there are some high spots. What and where was the palm sander used ? have you tried using a graphite stick or #2 pencil and burnishing it in on the hardwood inserts on the keybed ? Also check for any play in the shift trap works or places where the shift iron is rubbing ? The teflon powder on the keybed may be shortlived so perhaps some prolube or other product (McLube ?) is worth trying

David,

This is why we get the big bucks!  You can get every suggestion from every tech in the US and Canada, but in the end it's you and the squeak.

Go watch a few episodes of House, then come back and meditatively attack the problem as though your life (or the piano's life) depended on it.

Good luck and let us know what it was!

David,

I have had many such mysterious squeaks and groans on soft pedals, below are a few that I have found.

The top of a dag/dog can be tight against the back of the key frame.

The shift lever can rub on other trap work under the piano.

The top of the shift lever can rub against the top of its notch under the key frame.

The shipping screw (when present) could have been left up or could have moved up with time and service calls and can rub against the pin block.

The lifter rod can squeak in its bushing.

The lifter rod gromet can squeak or groan in the pedal.

The lyre can have loose posts that are groaning.

The lyre box can have loose screws or squeaky hinges.

The lyre felts can rub against the pedal.

The key frame can have loose boards that are moving against each other.

The key bed can be moving against its attachment points.

The lyre support rods can be loose and creaking against the lyre or piano body.

The top of the monkey could squeak against its lifter post (pitman).

The sostinuto rail could be rubbing against a damper part or lever.

The piano legs could be loose in their plates or could have a loose joint post.

The piano could be rubbing against  a wall or other object.

The bench could be creaking instead of the pedal.

The cheek blocks could be loose and moving.

The key slip could be rubbing on a card or felt placed between the key slip and action.

Isn't this job fun!