Volvo 1800 Master brake cylinder/Brake line

A single-circuit brake on the earliest cars loses all pressure from a single leak – which is why circuit type, motor (B18/B20) and chassis number determine which parts actually fit. The switch to the dual-circuit system happened from chassis 28300 (1969) as the B20 replaced the B18, and at chassis 7000 new brake components appeared. When rebuilding tired master brakes and rusty longitudinal brake pipes, these are the typical checkpoints.