BUCKET AS 2389525 - Caterpillar

Illustration 1 g01200873
Location of pressure switch for Service brake and retarder
(1) Air pressure sensor
(2) Secondary brake and parking brake pressure switch
(3) Service brake and retarder pressure switch The service brake and retarder pressure switch (3) is located behind the cab next to the ROPS on the right side.Some input signals to the Power Train Electronic Control Module (Power Train ECM) during a shift can cause a hunting condition of the transmission. A hunting condition is a series of rapid, unwanted transmission upshifts and rapid, unwanted transmission downshifts. A hunting condition is caused by ground speed changes near a transmission shift point.The Power Train ECM is designed to prevent a hunting condition. After two seconds, the Power Train ECM will allow one shift back to the original gear.In normal operating conditions, a rapid shift may be necessary. An example of a normal operating condition is stopping the machine. If a rapid downshift is not made in this example, the engine will stop. When the service brake or the retarder is used, the service brake and retarder pressure switch (3) will signal the Power Train ECM that rapid shifts are necessary.The service brake and retarder pressure switch (3) will signal the Power Train ECM when a higher engine rpm is necessary for an upshift or for a downshift. The service brake and retarder pressure switch (3) also signals the Power Train ECM to allow rapid shifts.When the service brakes or the retarder are not used, the Power Train ECM receives a ground through the service brake and retarder pressure switch (3). The Power Train ECM will use normal engine rpm for upshifts or for downshifts. The Power Train ECM allows only one shift back to the previous gear to occur for every two seconds.When the service brake or the retarder is used, the Power Train ECM will allow rapid upshifts and rapid downshifts in order for the machine to stop quickly. The downshift point will also be raised. This will maintain a higher engine rpm during downshifting. This function maximizes the amount of cooling oil that flows to the brakes during braking. The service brake and retarder pressure switch (3) is open when either the service brakes are used or the retarder brakes are used.