Brian,

Thanks for the info.

I have no aux vacuum pump, nor any engine smoke.

I will check the brake booster tomorrow when there is daylight. It is possible a connection could be loose, or perhaps some rubber has deteriorated. Would such a vacuum leak on the Booster hose also explain hard shifting?

By "hard" I mean there is a clunk from the differential when I lift off the accelerator. The hard upshifting is abrupt and jerky at times, unless I am feathering the accelerator, at which times shifting can be imperceptible.

I was reading in other threads that a leaky or failing brake booster will make a hissing noise when the brake pedal is pumped. When I pump my brakes, the sound I hear could be hissing, but then again it could be just the normal sound. I can't quite tell.

__________________
2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black