You may have noticed the big shiny chrome trumpets on the front fenders. These are emergency air horns, which are similar to truck and train horns except they apparently have a different tone, designed to be even more annoying and attention-grabbing with what the manufacturer dubs “Stuttertone”. They’re made by a company in Los Angeles by the name of Grover Products who’s motto is, cleverly enough, “The Sound of Safety”. The horns are air powered and actuated through a solenoid valve which is activated either by a button on the steering wheel or a switch on the center dash within reach of the passenger. I assume this additional switch was to allow the driver to focus on driving while the other person could operate the horn.
The truck also has a pair of traditional electric horns which are operated by pressing the center pad of the steering wheel, though they’re not particularly interesting.
I plan to replace the solenoid with a manual valve which will be operated by a traditional pull chain mounted in the headliner near the driver’s window. No sense having air horns and driving a big truck if you can’t use them like a trucker. Initially though, I just wanted to clean and polish them.
These are called adjustable horns but that really just means you can dial in the optimal sound, not change the actual tone of the horn. While there is a maintenance manual available it doesn’t really adequately describe how to tune them. Once I figured out the mechanism of how they made sound it was a simple matter of adjusting the screw threads to get them to the optimal adjustment.
Once I had them reassembled the next obvious step was to test them. I decided the air gun assembly on my air compressor would be a perfect press fit for the air input on the horns. I had blown these horns while driving the truck north so I knew they were loud. Before pulling the trigger, I put on ear protection and I was still startled by the shocking amount of sound that came out of just one horn. Rated at 125 dB each, you feel it in your chest as much as you hear it.