1992 300SE 5-speed automatic
 

My 5th gear (overdrive gear) didn't work when I purchased car used. Replaced microswitch on side of shifter box and it worked! Then it stopped. I have continuity on switch, I have replaced the shift solenoid, valve body, transmission internal wiring harness, transmission "brain" and checked resistance on ground from battery to trans. Help! I'm at a loss what to do next.

Tim

You need to have the trans computer scanned for codes! A common failure is the overdrive trans solenoid on the valve body, but reading codes will start the diagnostic process.

Doc,

This was done and no codes appeared. It did show that the tripping of the microswitch at the console registered the proper milliamp signal. The solenoid is new and the brain is new. Any ideas? One suggestion was that the two filters under the valve body may be clogged but I'm not sure of that.

Tim

Found the problem...a break in the plastic vacuum line in a place that was out of sight. Cheap fix!

Tim

Congratulations, would that be the vacuum line for the up shift delay actuator. What color was it?