The discs state to use only resin pads. Can I use something else?
This is a kinda deep question and requires a long answer. I can see where the confusion comes in but I'll try and be brief.
There are really just two kinds of brake pads in the affordable world - resin (also called organic) and sintered (also called semi-met, sintered metal or just metal). Many manufacturers list all sorts of other exotic stuff like Kevlar, ceramic, carbon and the like. Other than pure carbon discs used on very fast cars, all the other exotic stuff is just some exotic stuff mixed in with either metal or organic compounds.
Organic compound pads are made of tough high-friction fibres (Kevlar, asbestos, aramid, ceramic etc) set in a phenolic resin. This phenol stuff is made with carbon-chemistry and that branch of chemistry is called organic. It doesn't mean it is made from leaves and stuff but from long or short carbon chains. Alcohol, petrol, plastic and epoxy resins are all organic compounds. The phenolic resin has a low melting point and works with a type of friction called adherent friction. In short, it means that the pad material adheres to the disc material and in friction it is resin on resin. The disc steel underneath is just a platform for the resin layer on the disc, hence the use of cheap steel which is marked resin-only. In use, the pad material migrates from disc to pad and back. Obviously on new discs, a layer of the resin has to build up before the brakes work properly. Because the layer can just grow and grow, they also add some abrasive stuff in the pads to keep the disc-based layer in check. This is where the problem comes in, They cannot predict how you will use the brakes. If you use them too hard, the friction material will completely remove sections of the resin layer. If you use it too soft, the resin layer will build up. This build-up or abrade-off sections are not uniform and we get cyclical noises at a very high pitch. It is actually the pad material vibrating at the frequency of the screech. Other components pick up the harmony and sing along. It is difficult to tune-out these harmonies.
The transfer layer is invisible unless it starts to build up in hot-spots. Then you can see it because it looks different to the rest of the disc. However, it still doesn't look like pad material.
If you are still following, you'll notice that I have not yet mentioned the other type of friction. This is called abrasive friction and pretty self-explanatory. The pad and disc abrade each other to create friction. This means the pads (and disc) has to be very durable. These operate at very high temperatures and are only effective at these temperatures. These temperatures would make resin pads smoke and stink like a bus handbrake left on for 10 miles. The abrasive action is very noise right out the box. To control that and the kick-in temperature (make it lower), these pads contain not only metal but also some organic material such as Kevlar or ceramic fibres. Yet, they are predominantly metal. They contain iron, copper, zinc and tin in powdered form which is compressed in a cake at a temperature just below melting point. The texture is unmistakably crumbly. Because they do contain some organic material, there is also some adhesive friction involved but to a far lesser extent than in a pad with a pure resin base.
To (finally) get to your question: Can I use something else? The answer is maybe. Find a pad that is metal-free. You may have to troll through the marketing BS to find what you are looking for. They may call it a Ceramic Pad or a Kevlar Pad. I don't know. As long as it is not primarily sintered, you can use it. You can't use sintered metal pads because your disc material is not capable of abrasive friction.
Experimenting isn't that easy though. You have to clean the discs between different pads. Otherwise you don't get the right layer laid down on the disc. Disc brake cleaner doesn't remove the stuff. It is hard. Very hard.
If I were you right now, I'd try some different pads in the non-metallic class and try them out of the box without cleaning the discs, but with proper bedding in. If that still makes turkey noises, I'd then sand the discs and start again. Once you find your poison, stick with it.
