I'm a dedicated cycling commuter in a city that is not particularly bike friendly. I've been a devoted fan of the AirZound bicycle air horn (http://www.airzound.co.uk/) since I first encountered one about 15 years ago. They are wonderful if you ride a mountain or hybrid bike but they really do not work well on a modern drop bar road bike. I've successfully modified two AirZounds for road bikes using different approaches and have documented them both here. Both methods require splicing in an air valve between the bottle and the horn.

Version 1: Auxiliary Valve Using Schrader Stem (see my other posting(s))

Version 2: AirZound Valve Relocation (this document)

Both methods work. Version 2 requires a little more patience but I think the result is more robust.

Step 1: Shorten the Hose

Well... This is what I did. In retrospect, it might have been easier to go buy some flexible hose. It worked out fine for me though so I'll provide the step.

Ensure that your horn is depressurized!

Lift the soft plastic cap from the air can
Using a crescent wrench, unscrew the hose assembly from the air can. Be careful not to lose the o-ring
Pull back the ferule (black plastic in photo) on the hose
Remove the hose from the barb on the gray threaded fitting
After carefully sizing the length of hose required to go from your preferred air can placement to you preferred switch placement, cut the excess from the hose and hold on to it. You will need this in a later step.

Reverse the steps above to reassemble. Some tips:

Remember to thread the shortened hose though both the soft cover and the ferule.
Pushing the hose onto the barb is easier if you warm the plastic with something like a hair-dryer.

NOTE: If you decide to skip this step and buy additional hose, you may need to drill different diameter holes in steps 3 and 5.

Step 2: Separate the "Switch" From the Horn

Carefully separate the valve/switch assembly from the rest of the horn using a fine coping saw. You will wind up with the two pieces shown above.

CAUTION: Be very careful not to damage the hose. My advice is to remove some of the plastic retaining the volume control, remove the volume knob, pull the hose out of the way and tape it.

Don't worry too much about damaging the bell of the horn. It can be fixed/sealed with epoxy if need be (don't ask me how I know).

Step 3: Add a New Exhaust to the Valve

Using a toothpick or similar device, remove the square of plastic surrounding the hole where the switch used to vent air to the horn assembly (I'll call this the "exhaust port"). Look carefully - you'll see it.

Carefully insert the blade of a screwdriver between one side of the switch assembly and the hose in order to protect the hose. (see middle photo)

Drill a hole using a 9/64" bit (see footnote) on this side face VERY CLOSE to the original exhaust port (see all 3 photos). You can use either side. The photo resulted in the exhaust hose facing upwards when the switch was mounted on my left handle and this made sense on my bike.

Insert one end of the hose that you saved in step one. Push it through to make sure it clears the rubber liner but don't allow it to get blocked by butting up against any of the other stuff in the chamber.

You are essentially working towards the third picture BUT THERE IS A CATCH. The inside of the switch assembly is lined with flexible rubber. You absolutely must make sure that this rubber is not allowed to block the new exhaust port formed by the hose inserted into the hole. I ended-up using tweezers to pull the rubber through the old port and a pair of side-cutters to snip off a size-able chunk. Don't worry about overdoing it. It is essential to keep the hose from getting blocked.

Reinsert the square that you removed at the start of the step. You can cut-off one the arm on the side of the new exhaust, just to be sure. This piece of plastic doesn't do anything except provide a gluing surface now.

Note: 9/64" is based on the hose that I've found on all of my AirZounds from different eras. Your mileage may vary, especially if you substitute your own hose in Step 1. To be sure, drill a hole in some scrap plastic or wood and confirm that whatever hose you are using fits snugly without crimping.

Step 4: Complete the Switch Assembly

Using a saw or rotary cutter, reshape the large diameter mounting bracket that came with you AirZound according to the photos.

Use liberal amounts of epoxy to glue the switch assembly to the mounting bracket and to glue the new exhaust hose to the side of the switch. If you have the time and patience, I suggest skimming some epoxy over the old exhaust port and letting it partially cure before mixing up a fresh batch of epoxy and gluing the whole assembly. This will reduce the likelihood of epoxy flowing into the chamber through the old hole.

Step 5: Enlarge the Input Port in the Horn Assembly

Using a 9/64" (see note below) drill bit, carefully enlarge the air hole going into the horn assembly. There is a very fragile foil diaphragm just beyond the existing hole so my recommendation is to just twist the drill bit by hand without any significant pressure. It is tedious but puncturing or even denting the foil is bad news.

Yup, you guessed it, connect the other end of the hose that you inserted into the switch assembly into this hole and daub epoxy on the outside to keep it in place. Feel free to size and trim the length based on your mounting strategy first.

Step 6: Mount the Sucker and Enjoy

If you've gotten this far, I'm sure you don't need help installing the system on your bike. I've included a few photos showing how I mounted the new trigger switch and showing how I am able to activate it. In my normal riding position with my hands on the brake mounts, I'm able to activate the horn easily with my middle finger (appropriately enough). If I'm in the drops, I can reach up and over with my index finger.

Unlike my first version, this doesn't require any special techniques for refilling the air tank, you don't have to remember to tie-down the actuator on the horn itself and it weighs a few grams less.

Happy cycling...

...Pete