My rear brakes on the 1982 2CV make a noise like a badly played bugle when I apply them at low speeds (and only at low speeds). I really don't need to use the horn when approaching a T junction.

Occasionally, I get the same noise without my foot on the brake pedal, when moving off from stationary.

It seemed dead obvious to me that the brakes must be binding (and maybe they are). But the last 5km to my house is all uphill, so I can easily drive the whole way without touching the brakes. When I get home, the rear brake drums are absolutely cold. I thought this was a definite test.

I've owned the car a long time, and I'm certain that nothing but LHM has ever gone in the master cylinder.

At the latest CT (= MoT), about two weeks ago, the rear brakes were OK as far as the braking forces were concerned. They didn't mention the noise, possibly because they test them with the wheels spinning fairly quickly.

Any suggestions about what might be causing this?

Any play in the wheel bearings?

Roger - I haven't checked the rear bearings for play myself, but they'd have picked that up in the test for sure. When it stops raining I'll have a look.

you can try to file the front and rear edges of the ferodo material under 45 degrees.

I have had no luck curing my noisy rear brakes, but I have spent a while going through the good French 2CV forum, where this issue has been raised repeatedly.

The views there seem to fall into two mutually exclusive schools.

There are a lot of people who say that what you need to aim for is to make the linings touch the drums better, by re-profiling them with a file or by better adjustment of the eccentrics.

Others say it's what the linings are made of, and that this wasn't a problem when they contained asbestos, or alternatively when they were made of a more recent compound that is unfortunately also no longer available.

Quite a few people say they have tried either one of these two approaches, and some say they have tried both. Some report success, and others (the majority) say that after trying everything the brakes are just as noisy (or worse).

There was one quite different suggestion I wondered about. If the noise is from the drum back-plate, stopping it acting as an amplifier might be effective. So what they had done was weld a shaped metal piece between the swinging arm and the backplate (I have to add - I think this was where it went - there were some French informal technical terms I couldn't find in the dictionary).

Has anyone either heard of this - or even tried it?

I have heard about this , but have no experience in doing so.
On the Dutch 2CV forum this procedure has been mentioned before.
The suggestion came from an ex Citroen mechanic.

I had issues with a very noisy rear brake, really embarrassing and annoying, which took years to get to the bottom of. The problem was eventually pin-pointed to be a cross-threaded stub-axle that the hub nut fits to. It never came loose or cause any other issues (like vibrations or undue tyre wear). The entire suspension arm was replaced and the brakes have been quiet ever since.

You should open up the drums and check for play and damage.
It may be worst than you think or hope.
It may be dangerous. Very.

The 9” nail between the drum and the arm is an old bodge.
However, changing the shoes and making sure they’re properly set up with eccentrics not concentrics usually fixes it, as far as I know.

Ever thought about the springs not being strong enough any longer ? Over time their strength weakens because the metal gets tired. In this case the brake shoes can move too much and when braking they can start to vibrate.