CAV ZB starter (early E)
The ZB starter was used with a 126 teeth ring gear and the ZBB with Bendix drive a 128 teeth ring gear. With the latter, the diameter of the flywheel had to be reduced to clear the Bendix pinion. The position of the toe board also changed slightly: the ZBB shaft with Bendix drive is longer, and otherwise fouls the toe board.
Bendix Drive 'The mechanical hand that cranks your car'
During 1921, CAV updated their electrical equipment, replacing the coaxial pre-engaged CAV ZB starter with the ZBB type, including a proprietary Bendix drive to cushion the pinion engagement. The floor mounted, two stage switch was replaced by a simpler push button, mounted on the dash (at the same time the D type Vauxhall was similarly updated). This later type has proved to be more robust over time, with the exception of the Bendix drive spring: the service sleeve is often missing, and spring failures are common.
The original Bendix spring part number is L13-6X, and original springs are stamped 'Bendix'. Replacements are available from the Register. Note that the springs are Left Hand wound, and, being of American origin, the spring drive bolts have UNF threads.
The Bendix Drive catalogue* shows all the parts which comprise the assembly.
* Catalogue kindly supplied by John Kent