The use of a square drive interface between a wiper arm and its motor or linkage shaft has proven to be advantageous on numerous modern OEM railway applications. They provide an ability to fit the arm in the correct park position first time every time and are also significantly more resilient to the problems of spinning on the traditional tapered DIN spline interface as a result of bird strikes and/or inconsistent fitment standards. As a result of this a number of operators have identified that the benefit can be read across by retrofit to older vehicles by changing the relevant components to the new design.
Many of the older vehicles were built with a pneumatic BPM wiper motor that was directly coupled via its stainless steel output shaft through the bulkhead and onto the DIN taper spline wiper arm. It will be seen from the adjacent illustration that the process of changing the shaft is a simple substitution of one for the other.

In cases where the wiper arm is of an arcuate type the changing of the shaft and the fitment of a corresponding arcuate wiper arm is all that is required. If however the vehicle is fitted with a pantograph wiper arm then in addition it will also be necessary to substitute a new slave arm swivel post in place of the existing swivel post as illustrated by the corresponding leaflet.

DIN Taper Shaft
Square Drive Shaft
Class/Type
DIN Taper
Shaft
Driver's
Side Square
Drive Shaft
Assistant's
Side Square
Drive Shaft
43
771121
M402119
M402120
60
771821
M402121
M402122
141/142
771130
M402000
M402000
143/144
771124
M401989
M401990
150/1 & /2
771124
M401991
M401992
153
771122
M401993
M401993
156
771123
M401995
M401995
158/159
771858
M401922
M401923
507/508
771128
M402096
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