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AW55-50SN Harsh or Delayed Bump Reverse Engagement

Tuesday, September 2, 2014 - 07:00
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This transmission is notorious for solenoid malfunction causing a wide variety of shift complaints. One of which can be harsh garage shifts into gear such as from Park to Reverse. In this scenario, a harsh or delayed reverse bump engagement is felt so an exchanged rebuilt or new valve body has been installed, all pressures were within specification and all shift adapts have been performed yet the harsh reverse engagement remains.

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The Direct Clutch frictions (C2) located in the back or end cover comes in two (2) different thicknesses. For 2004 and earlier applications the friction plate thickness should be .068”. For 2005 and later applications friction plate thickness should be .059”. The steel plates that go in-between the friction plates remains the same for all applications which is .071”.

The problem that arises is using incorrect thickness friction plates making the clutch pack too tight. If the clutch clearance is too tight the geartrain is already in partial rotation when the selector lever is placed into reverse. The harsh shift felt is due to the sudden stop of the rotating geartrain.

At times friction plates have been known to be .002” to .003” thousandths out of spec which can also cause clutch clearance issues.

The C2 clutch pressure plate is selective but with incorrect friction plate thickness a proper thickness pressure plate cannot be found.

C2 clutch clearance specifications are: 0.76 - 1.24 mm (0.030 - 0.049 in.)

The available selective backing plate thicknesses are:

3.6 mm (0.142 in)

3.8 mm (0.150 in)

4.0 mm (0.157 in)

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