It's funny that most guys on this site always point to the switch over valve as the problem when responding to an owner with a code #26 upshift delay valve problem. I guess it's hopeful thinking as the part is very cheap.

However, my MB mechanic, the famous Enrique of MB Motors, who has worked at MB delearships on 3 continents for about 40 years, and has owned his own shop for the past five years, tells me that he rarely, if ever, replaces these switch over valves.

95% of the time, the problem is the vacum diaphragm on the transmission no longer holds vacum. It is not a cheap part - about $250-ish, if I remember correctly.

I watched Enrique diagnose mine. He pulled the vacum hose off of the switch over vavle, applied vacum with a vacum pump, and we could watch it immediately lose vacum.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".