Torque coupling allows lighter vehicles

Certain turning car parts have to be strong (and therefor heavy) to resist sudden torque. For certain of them it seems to me one could use a slippage device such as brake pads or two powerful permanent magnets connected positive-to-negative to lessen the maximum stress these parts need be expected to withstand.It could look like this:

---part A--(MagnetA)(MagnetB)-Part B---

If sudden torque is applied the devices would slip against each-other until their rotational speed matches. Otherwise they would provide a coupling like a single piece of metal.

edit: This could also provide energy absorption in certain accidents.