Greetings VenKat,

If you are experiencing high RPM's before the shift takes place, high being 3000 rpm then try screwing in your bowden cable adjustment a turn or two and test drive the car again. This should lower your shift point rpm's and also allow fourth gear to kick in. Screwing the adjuster out will raise the rpm before shifts and if to extreme will not allow the shift from third to fourth take place. Proper adjustment should have you shifting into fourth gear with moderate pedal pressure around 2800 to 3000 rpm.

Just a thought to look into,

Charles

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'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan