How to fix Sqeaky stair when bracing fails to solve problem

[kez1]

I have a squeaky stair that runs at 30 deg or so from the ground up to a balcony.
I can get under the stair to fix it and thankfully there is no tread or carpeting on top so I can get in at the top too.

I have braced across each stair from the top until half way down and this has eliminated the squeak in the top half of the stair.
I have started bracing the bottom half of the stair but this is not fixing the squeaks.
Half way down the stair it is supported underneath.
I am wandering if the support may have introduced stresses which cause the bottom half to squeak.

I've also put loads of tightening screws in, all over the place.

Thinking I need calk visible gaps where sound is originating.

What's the best calk/ filler for the job?

Any other ideas?

Photos to follow when I get back to the computer later ...

 

[KenGMac]

kez1, good evening.

One method I have seen to work is to get a hold of triangular shaped strips of timber, each face about 20.mm / 25. mm If you purchase a length of such material you can cut it into 30.mm 40. mm lengths.

Next using PVA or Gorilla wood glue [other such wood glues are available?] glue the triangles on to the underside of the stair.

There is a wee trick in that when you place the triangles with glue on all mating faces rub the triangle slightly left and right to remove any air bubbles from the glue

Place 4 / 5 / 6 triangles between the "tread" and the "riser" and between the tread and the Stringer.

Another trick do NOT use the stair until the glue has set, meaning fit the triangles, it appears you have access to do so, then ban the use of the stair until glue set, longer if possible?

Question? are there any long thin slivers of timber between the treads and the stringer? If any are loose re-glue them and tap them in to ensure they are firmly fitted.

Fillers will act for a very, very short period of time then creaking will start again.

Ken