| 摘要 |
PURPOSE:To drain muddy water penetrating through communicating holes and prevent an oil seal from being damaged by muddy water, by a method wherein at least one auxiliary communicating hole aligned with a main communicating hole in the axial direction of a dust boot is provided at another inside root trench part. CONSTITUTION:The passage of air in response to a change in the capacity of the dust boot 4 at the time of moving a striking rod 2 in the axial direction is permitted through the main communicating hole 4c and each of the auxiliary communicating holes 4c'. In that case, even when muddy water penetrates through the main communicating hole 4c or some of the auxiliary communicating holes 4c', muddy water is drained to the exterior through the holes 4c, 4c' located at the substantially lowermost parts, before it can move to the oil seal side. In addition, the dust boot 4 is prevented from rotating, by clamping a projected part 4a of the boot 4 by a recessed part of a collar 6 fixed to a housing 1. |
