Greg, one of the better old compressors to use as a vacuum pump are the one's off Old Ford products. They have a sump and you can just put some oil in the bottom, hook up your suction side hose, rig up an electric motor and pulleys to power it and off you go. You won't be able to pull a deep vacuum like the new 2 stage vacuum pumps but it will work for garage use. They have a tapered shaft so it's a little tricky to mount the pulley but nothing you can't handle. My buddy has been using one for years.

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Orland Park, IL
1985 300SD 215,000 miles