soontobered84

I like the sound of the older style trumpet horns. I have replaced the newer style horns with trumpet style horns on my GTS.

The problem: the longer trumpet doesn't work correctly.

First issue: I took the dang thing apart like a dummy and didn't put it together right away. There are several washers inside and I was not 100% sure of the sequence.

Second issue: There is an adjustment screw on the back of the body of the horn that can be screwed in and out to adjust ???

Third issue: If I plug the horn up without the trumpet, and push the button, it sounds as if it should work but when I screw the trumpet to the base tight, it does not work and only makes a small sound as if it is trying but something inside is amiss. From these sounds, I know the solenoids inside are working correctly.

Does anyone have a pictorial or a schematic showing the guts of a trumpet horn and the correct configuation of the washers etal.??

linderpat

following. I've taken apart 2 of them, and put them back together exactly as disassembled, but could not get the sound quite right. The screw on the back is for adjustment. Need one of the gurus to tell us what to do on this (MrMerlin where art thou?)

Mrmerlin

to make the horn work takes a bit of trial and error,
the adjustment screw is to preload the part inside the horn to have just enough flex so it can move at a high frequency, thus the sound.

turning the screw in small increments should give you an idea of how the vibrations can change with the preloading screw changed.

That said I have only gotten a few of the horns I have messed with to come back to life.

NOTE use green loctite on the adjusting screw when you have it set to offer the loudest report.

NOTE usually rust/ corrosion forms inside the horn to reduce the vibrations, these are harder to restore performance.

OR one of the coils has a wire break close to the solder joint,
these are easier to get working as its simple to resolder

Not much to lose here with experimenting to get the horn to work.

You also have to remember that a lot of the parts on the 928 are made in such a way as that they can be taken apart and adjusted or worked on to restore performance.

Here is where being mechanically minded will pay off as most parts can be restored to operation

New cars are usually hard crimped or soil potted devices that are throwaways once they stop working as they should

GlenL

I've tried this a number of times. Usually they'll come back to life, or a while, just by working the screw on the back. But...they don't last. I've got a few and I seem to rotate them hoping the next one will last.

soontobered84

Thanks for the response guys. This horn keeps trying to work, but I think I have moved the washers on either side of the metal diaphragm around too much. I tried putting them back according to inside diameter hole which helps a little bit, but I'm just not sure. I'm also not sure whether I should move the adjustment bolt much until I get the washers correct.

Does anybody have a picture showing the internals of the horns: specifically the metal diaphragm and the washers surrounding it?

Additionally, my perception is that the metal diaphragm and the post that attaches to the metal diaphragm (with the washers and the nut) just sits on the adjustable piece that goes between the solenoids. Is that correct?

soontobered84

In the interest of furthering our collective knowledge on this website, I perused several other websites looking for horn repair and used the knowledge gained on those websites to fix my horn until it was really broke. I learned that 12V 15A will let the smoke out of the wires inside the horn unit, so for all you following at home, don't use that many amps.

Adk46

I prefer a French horn over a trumpet, although they can pose their own difficulties.

More seriously, I can imagine that the vibrating bits inside a car horn may require the same sensitive adjustments as are necessary to play a wind instrument. A permanent "injury" to the "lips" means retirement is in order.

soontobered84

LOL. Well played Curt.

I do have pictures in my phone of the horn guts and a pretty good idea how to fix those horn guts, but I'm having issues posting the pictures for some reason. Before I de-smoked the wires inside, I was getting a squawk and was on my way to fine-tuning it to get that nice "trumpet" sound, but then it went "ppppfffffpppp" and a little cartoonish wisp of smoke curled out of the horn base.

Pictures soon.

SMTCapeCod

Been through a few 928s and my current one is the first I've had with defunct horns- and it had the easiest past life of them all!

Edit 6/10: and wouldn't you know it, found the sweet spot on the MOMO button and it's working again! At least the high tone.