stop, mend
輟 centers on stopping an ongoing action or process, especially one involving movement or work. The meaning 'mend' can be seen as stopping damage or wear by repairing it.
輟 combines 車 (vehicle, cart) with 叕, which likely contributes the sound and carries a sense of connecting or stopping. The idea may be a cart that is halted or repaired.
A cart (車) with a tangled, broken connection (叕) needs to stop and be mended. Picture a wheel coming off and the driver halting to fix it.
For テツ, imagine a cart that stops with a metallic clang: 'tetsu!' The sound of iron (鉄, てつ) hitting the ground cues テツ, and the cart must stop for repairs.