Overtaking system on pre-war French trucks

Letters to the editor

Although pre-war trucks are not that often a topic in your mailings, I find them pretty interesting. I own a 1940 Citroën U23 truck, ex French military with a fully documented history.

One of the parts that remained after restauration (I bought it completely dismantled) is some 25 cm big horn. It looks a bit like a claxon but it’s not. I finally found out that it’s supposed to be mounted in the cabine, pointing at the drivers’  ear.

I learned this is part of a system that used to have 2 horns; the second one to be mounted at the rear end of the truck, pointing backwards. The two were connected with a big hose, and a green light made the system complete.

The purpose of this system is for upcoming (faster) traffic to announce they want to pass this slow truck. The faster car blows his horn, the sound of which reaches the ear of the truck driver by means of the two horns. If the road is safe for taking over, the truck driver lights the small green light at the back of the truck, giving the faster driver the sign to step on the gas.

I found it very hard to find any documentation on this pre-war system, let alone the parts I miss to make mine complete.I only have 2 or 3 pictures of similar systems, coming from France. The brand involved could be Tirette.

If this topic is of any interest to you please do not hesitate to contact me. I’d be happy to share what I have and see what the cat brings in.

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The first photo (3966) is from a 1940 Citroën U23 scrapped for parts, ex armée Française. Credits Alain Chaussade .
This one is exactly the same as the horn I had left from my own car (also 1940, ex-armée). I can take detail photos of this if required.
The second is a very poor photo of a similar horn in a 1936 Citroën truck type 32 (converted immediately after the war from bus to truck, handmade wooden cab copied from a Berliet GDR).  The third photo shows the corresponding horn at the rear of the T32 and the fourth the corresponding green light operated from the cab. Photos 2-4 credit Ivan Lavallade.

Regards, Sander