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Your parking brake issue is probably the ratchet teeth worn away from years of owners just pulling the handle up and causing the ratchet pawl to click over the teeth resulting in the ratchet teeth wearing down. You may be able to file them back into shape so the pawl engages deeper or find a good used one from a breaker. to avoid this wear problem always press the handle button when pulling it up so the pawl doesn't run over the teeth causing wear, once fully up release the button so the pawl engages in the set position. Not the best parking brake set up on these cars you must ensure the shoes in the disc/drum are adjusted to spec and the cables are free to move and in good condition to get a good parking brake.
to the forum from me in Stafford. Not sure what you mean by the Emergency Brake. Didn't know Z3s had one
