The horns on my 1970 240Z had quit. After 38 years of heavy weather and road salt flying up into their throats, they no longer sounded like horns. They just sort of 'squawked' and 'tweaked'. And they no longer resembled horns. They looked more like a pair of barnacle-coated Cape Cod oysters, sitting there on the crossmember between the front bumper and the front of the radiator.
My Z had been restored, but the horns had not. I was prepared to replace them, but decided to try to resurrect them first. If I killed them completely I was intending to buy new horns anyway, so no loss.
I removed the front bumper to have it rechromed, which gave me access to the (4) 12mm capscrews which hold the two horns in place. Today I ran both horns thru the sandblaster, spending about 10 minutes on each. They came away brilliant and looking new! I can even read the writing on them.
I removed the sound adjustment screw from each (the locknut requires a 1/4" socket, which fits neatly down over the screwhead). I cleaned the threads on both screws and replaced them to the same depth. I tried the horns on the battery top and Voila! Both horns gave me 110db of full Datsun voice!
I spraypainted both horns flat black (RustOleum) and remounted them. Now my Z has it's original voice again ~ for free!
Don't throw out your old horns! Yours can NOT be older than mine were, so they can probably be saved.
Frank T