BMW E60 automatic transmission mechatronic unit and solenoids
Do the solenoids need replacing when the mechatronic unit is opened?
Replacing them at the same time is worthwhile, because the extra work is small. The solenoids also control the torque converter. Repairing only the mechatronic unit can leave the fault in place if the symptom is caused by the solenoids.
Which solenoid kit and separator plate fit?
The number on the gearbox type plate (1068 xxxxxx) tells which solenoid kit is needed. For the Gen2 GA6HP26Z gearbox, kit ZF 1068 298 047 was used. The separator plate for the 6HP28X gearbox is ZF 1068 227 065; 1068 227 063 is for the other 6HP gearboxes.
Which seals should be replaced?
The two-piece square seal between the mechatronic unit and the gearbox should be replaced. The solenoid seals usually come with the kit, but not always. The foam insulation on the solenoid bridge protects against metal particles, and it is cleaned or replaced.
How is the mechatronic unit taken apart and assembled?
Take it apart the right way up on a bench, so the balls and springs stay in place. Fit the control unit in place before joining the halves, so the locating pins line up. The screws that go through it are tightened last, otherwise the plastic may crack.