Mercedes-Benz W126 automatic shifts late and vacuum leak
280 SE300 SE
Why does the W126 automatic not upshift in time?
The cause can be the vacuum hose to the transmission being disconnected or leaking. The transmission then thinks the throttle is wide open and the upshift is delayed. The shift may only happen at full throttle at the rev limiter. The repair is often cheap.
What affects the W126 automatic's shift points?
Cable tension sets the shift points and vacuum sets how firm the shifts are. The kickdown cable and the vacuum module determine which gear kickdown forces. The needle of the vacuum gauge shows whether the system has a leak.
Why does the W126 automatic act up and the car smoke?
The modulator (pressure-compensating vacuum regulator) on the side of the transmission may be broken. When its diaphragm tears, oil leaks and is drawn into the intake manifold, and the car smokes. The regulator is checked and replaced if necessary.
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