If there are two vacuum lines, one on each side of the vacuum chamber, there will be a vacuum assisted shift both ways. You're probably getting a little bit of flex of the rubber diaphragm trying to pull the shifter in one direction, not fighting a spring.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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