Clean those inners

[CharlieB]

I had been playing the same (very good) trombone for eighteen years.
Then the intonation got quirky and the partials wouldn't stack.
No damage, no air leaks, and only this horn. ???????? Frustrating.
It was my fault.
I had been meticulous about cleaning the outer slide and crook, and the outside of the inners, but lately (dunno why) I had not cleaned the interiors of the inner slide tubes.
Sighting through them, they looked pretty good.......misleading.
After a good cleaning and polishing, the problems went away.
Amazing how much problem was caused by such a small amount of schmutz.

[Nolankberk]

I was having intonation issues until I cleaned mine out as well, it gets nasty in there

[tbonesullivan]

I run a Brass Saver brush through my inners at least once a week. "stuff" can build up very quickly.