Elastomer in bicycle trailer hitch: is it important? I have a bicycle trailer (Hamax Outback One). Recently I inspected the hitch as I was connecting the tow bar to the bicycle. The steel spring was getting rusty, but I do not think it's a big deal. However, inside the spring there was a black cylindrical rod which I assume is made of some sort of elastomer. That part seemed to have broken into two pieces.
I started looking for a replacement or a fix for that. There are a lot of similar complete replacement hitches sold online. However, the dimensions of the parts, especially of the coupler that stays on the bike's dropout, are slightly different, meaning I'd have to replace the whole hitch and buy new couplers for multiple bikes. Alternatively, a complete new tow bar for Hamax trailers can be found, but that is more expensive and really not something that I'd need.
On the picture below, the transparent elastomer part is sticking up out from the steel spring.

The question is: how important is that for safety that the elastomer is in one piece? I assume its role is damping when the spring gets compressed at braking.
Additional question is that if anyone has done that I plan to do, that is, to buy a no-name hitch and reuse its new elastomer alone. Or maybe there are other DIY sources of the elastomer part?
A spring, of course, is just a piece of wire.
When you bend a spring, you're just bending a piece of wire.
In a perfect world, the wire would bend evenly along it's entire (coiled) length.
In the real world, particularly during sharp or extreme bends it's possible for the wire to kink.


Either way, the kink becomes a weak spot and as with all metals when you flex them repeatedly in one place, they will break.
The flexible insert allows the spring to bend a small amount on it's own before the insert comes into contact with the spring's interior. That has the effect of spreading the bending forces across more of the spring's coils ensuring the spring bends more evenly along it's length and preventing a kink.
You could try replacing the broken polymer with a length of stiff hose filled with expanding foam. It might be weaker than the original, depending on the stiffness of the hose and foam, but they're common materials and easily replaced.
Just keep in mind: you or someone else, turned the bike so sharply you snapped the original material. Try to avoid doing it again.