Main slide lock not locking properly

[GTDon501]

I have a Bach Strad '75 36B. The main slide lock connecting the main body of the horn to the slide assembly (both inner and outer) is fully tightened, but when I hold the horn the bell (and body) rotates away from my neck and onto my shoulder. I know better than to get out the pliers.

[BGuttman]

It could be your tenon is worn (that's the slide part).

A temporary fix is to wrap a layer of Plumber's Teflon Tape which will build the tenon up just a little.

Proper fix is a replacement tenon.

[elmsandr]

The taper should hold it even without the nut being tight. Try just that. If it is loose, try cleaning it. REALLY clean and polished. Sometimes a quick wrap of teflon tape can help here.

There is a possibility that after 40+ years it is worn out. Either side could be worn, you could 'blue' up the joint and see what type of contact you get (if that doesn't make sense, machinists do it all the time to find high and low spots on tapers).

Cheers,
Andy

[Leisesturm]

Interesting question and answers. I just got a new horn. It is rented but it is absolutely brand spanking new (King 606) and it has the same problem as the original poster. The fully tightened main collar does not keep the alignment of the slide and bell section that I set. It's not 'floppy' by any stretch but its definitely not what anyone would call 'tight'. I actually was wondering what to do about it but that isn't why I joined Trombone Chat. I do have some teflon tape around somewhere. It makes me wonder though, how tight should this connection be anyway? If I do put tape on the join will I be able to get it off again when it is time to return the horn?

[Doug Elliott]

I have discovered that even a thin layer of ink from a marker, or some lacquer, or paint, or machinist's blue, will sometimes build it up enough to tighten. World's cheapest repair.

[LeoInFL]

I had the same problem when I first bought my Getzen. Turns out that the tenon on the slide was out-of-round. I have a graduated mandrel that made it round again and problem fixed. The mandrel looks like the ring sizer that jeweler's use.

[JohnL]

On a 36B, I would first do as Andy recommends and clean both of the mating surfaces thoroughly. Sometimes some of the lube from the valves migrates down to the tenon joint and causes trouble.

Stray lube is less likely on a King 606. Since it's a rental, you might just want to take it back to the shop.

[doctortrombone]

On most horns, you can see the ends of the tenon joints when the nut is not engaged. If there's no gap between the ends, and they're butted up against each other, you will never be able to maintain the connection between the two parts without some slipping.

[timothy42b]

The nut doesn't hold it. The taper holds it by friction. The nut just keeps that from decreasing.

Someone here, probably Ken, recommended lubricating it with just a tiny bit of tuning slide grease, after cleaning carefully, and that does seem to help.

[boneagain]

Someone here, probably Ken, recommended lubricating it with just a tiny bit of tuning slide grease, after cleaning carefully, and that does seem to help.

I'd be careful about lube on tapers and threads. Also about polishing.

the key is for the taper to be clean. Adding something to change the coefficient of friction (like bluing, as mentioned by Doug above) can help a worn joint.

Lube on things designed without lube in mind can lead to over torquing, which can stretch tapers and twist heads right off screws.

Yeah, if you are going to pack a thing away for weeks or months, some lube to keep it from corroding in place is fine. If you are keeping up with regular use, though, reducing the coefficient of frictino can exceed design paramters, shall we say?

[timothy42b]

Yes, I'd be careful what I lubed.

I definitely would not lube the threads. I think you might tighten the nut enough it might get stuck. I've seen people have trouble loosening them as it is.

I don't know about the taper. I've always just tried to keep it clean, but Ken (Naj) said it had helped to lube the taper. IIRC.

The other place you could lube, probably by accident, is the outside of the nut. Once you've done that, good luck getting hold of it enough to take the horn apart. It's kind of awkward getting a grip on it anyway, the way your hand has to wrap around.

[Bonearzt]

NO way I would lube the taper in ANY way!!!!
A bit of tarnish would help create some needed friction, IMHO.

Just get either the tenon or the receiver replaced!

Eric