My recently purchased 83 300SD, 146k miles, is flaring and double shifting between 3rd and 4th gear. The tranny was just flushed/filter changed, fluid level is correct. My vacuum reads 15-20 at the brake booster line, 12-15 past the tranny dashpot. The vacuum drops toward zero as accelerator advanced at the vacuum relief valve.

The plastic levers on the vacuum valves on top of the valve cover are completely gone, new ones are on the way. Could this be the main reason for poor shifting? I have yet to draw a vacuum on the modulator to test for leaks. That will be my next test after the new levers are installed.

BTW, I have read Brotherton's article, Peter Schmidts as well as several other DIY articles for diagnosing these problems. Thanks for any advice.

John

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Certified Registered Nurse Anesthetist (CRNA)
2002 F250 powerstroke with Plantdrive WVO conversion
1983 300SD 190K miles ,sold
2006 E320 CDI