If the car is stuck in 1st gear, the vacuum pump is the least of your worries, you likely have transmission issues or a misadjusted linkage somewhere.

Vacuum pumps tend to produce somewhere between 20-22mm/HG when working properly.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)