Elusive bass end air leak!

[knobby]

Hi folks,
My Galotta Continent has a slight air leak coming from the bass end which I am trying to locate and fix. It's not overly bad, it's just a little annoying.
If I push or pull the bellows reasonably hard I can hear the hiss (more on push than pull) which sounds quite close to my left ear. No notes sound when doing this. At first I thought it was the air release valve but I blocked it off completely and there was no change. I've taken the bass end off and shone a torch from the inside to see if I could see any light shining past any of the pallets but there isn't. I can't feel any air around the joint between the bass end and the bellows, but can feel some coming through the bass end where the bass strap adjuster wheel is.
Any idea where to look / what to try next?

 

[John Doe]

My commiserations- mystery air leaks are- to me at least- really annoying even when the instrument is essentially still quite playable.

Air coming from the area around the wheel with no notes sounding - though most bass reeds take enough air to sound that you could actually have a pallet issue even without the bass reeds sounding- makes the most likely sources as either the foundation plate to case seal- or any screws or bolts that go through the foundation plate. There are usually several to include through bolts that hold down the bracket that the foot of the bass blocks slide under.

The connections to the shifters through the case also might bear some scrutiny- though that would probably be heard from ... the shifter area.

And of course, the usual suspects of bracket or strap screws loose enough to leak.

A bead of some sealant (I just run a thin line of white glue around the foundation case juncture and about any through screws) might be a decent idea. Not knowing where the leak is you are of course whistling in the dark but if that's it it'll work and if not, no harm done. You're pretty unlikely to need to be pulling the bass plate for virtually any likely repair work.

Still stuck? To eliminate the pallets you can always pull the bass blocks, place a strip of paper over the openings, and replace the blocks. If the leak is unchanged the pallets weren't the issue. If it vanishes then- annoyingly enough, for bass pallets can be a true pain to repair- you know what you've got.

If you can feel the air coming from the bass end it's pretty much got to be foundation plate issues, or pallets.

I assume it's not some small pin hole in the bellows corners just up from the wheel? That would be heard/felt on the outside of course, not through the interior as you indicate. As with bracket screw leaks, sometimes it's hard to know just where the sound is coming from.

Not much help I'm afraid- it's a difficult thing to diagnose over a message connection- but it's what I would look at.

Good luck-
Henry

Sorry for typos

 

[Ventura]

through the bass strap adjuster wheel opening would suggest
the leak is into and through the bass/stradella chamber

from the bellows side, look for any and all hardware points
where the metal of a bolt or screw penetrates through the wood,
as it's tightness must maintain the airtight seal where it comes through

for the pallets/valves age and hardness and seepage are eventually
unavoidable, and if you eliminate all else, as Holmes has said,
my dear Mr Watson...

 

[kimric]

I use a stethascope that I have cut the disc off of and replaced with a small metal tube, You can find leaks by compressing the bellows while running the tip of the tube over suspected areas and between the pads. You will hear a sound like someone blowing in your ear when you pass over a leak. It can sometimes be confusing when you are dealing with pad leaks since the air can be moving at odd angles and it may be off to one side of where you hear the sound by several mm.