The upshift delay valve delays the upshift from 2nd to 3rd on both the W140 and W124.

And it is correct that it is not a function of "how far", but for "how long" it takes to warm up the catalytic converter. That is its only purpose - to warm up the cat. quicker.

The delay valve itself is on the side of the transmission, and it is operated via vacum. There is a switch-over valve that is mounted behind the brake master cylinder on the firewall, which provides the vacum to the upshift delay valve on the transmission.

95% of the time, when the delay valve starts acting up, it is the delay valve itself that is going out - usually because it doesn't hold vacum anymore.

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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".