Diagnosis is simple. The device that manipulates shift point is a vacuum element controlled bellcrank at the base of the control pressure cable. Follow the vacuum line from the vacuum element to the switchover valve. Disconnect and apply vacuum. Does it hold. Probably not, number one failure is the vacuum element itself. If it holds, go to the other side of the switchover valve and take the source vacuum line off and run the motor, doe sit have vacuum.

If you got this far and have no problem, tee in a vacuum gauge and wait till cold. Tee it on the transmission side of the switchover valve. Vacuum shoul appear when cold due to the control signal turning on the switch over valve.

No control verify the circuit. As a last step place a vacuum on the element and see if the trans shifts latter. The vacuum element is adjustable and I have seen them installed but so far out of adjustment that the computer still didn't see the rpms necessary for the first shifts.

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