a synchronizer unit eliminates the chattering noise generated when shifting a manual transmission into reverse from a forward gear while the drive shaft continues to rotate in the direction corresponding with the forward gear by providing a reverse brake arrangement for arresting rotation of the input shaft . the reverse brake arrangement includes a shaft rotatably supported by the transmission housing and a clutch hub mounted on the shaft which is adapted to rotate with the shaft . the clutch hub has a splined outer circumference . a shift sleeve is provided for engagement with the splined outer circumference of the clutch hub and is movable in the axial direction of the shaft . the reverse brake mechanism further includes a frustoconical cone in coaxial relation to the shaft and disposed on a first side of the clutch hub . the frustoconical cone includes a frustoconical surface on its outer periphery . a first blocker ring is coaxially aligned with the shaft . the first blocker ring including a conical surface adapted to be fitted on the frustoconical surface of the frustoconical cone , such that axial translation of the shift sleeve in a direction toward the frustoconical cone urges the first blocker ring against the frustoconical cone . the frustoconical cone is mounted in the housing for limited rotation and includes at least one tang extending therefrom .