The 6.3 tranny is a version of the early electrically variable modulator trannies. There is a "double" lifting solenoid on top of the tranny that moves the hydraulic valving such that modulator pressure varies from10-15 at idle to 35-50 at everything else except full throttle where it is above 60. The idle and full throttle positions are electrically controlled the middle position is default. A car stuck in default (no electrical function) will shift into gear extremely harshly.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician