[Pat Schmitz]

Correct Larry! (mostly!)

When I read your comments, I knew that my P337 did not have wet pumps - it actually does have Dry pumps with De-ice. Here is why:

From the Cessna Service Manual Page 14-9: The dry vacuum pumps are replaced with oil lubricated pumps and oil separators when the optional de-ice system is installed thru aircraft serials P3370052. Beginning with aircraft serials p3370053 and FP3370001 the vacuum pumps are replaced with larger capacity DRY vacuum pumps when the optional De-Ice System is installed.

So not all 337's have Wet pumps with de-ice - only those prior to serial 0053.

The service manual goes on to say

NO SUCTION INDICATED AT ONE SOURCE:

Probable Cause may be any of the following:
Defective Vacuum Pump - or
Disconnected, broken, or plugged lines - or
Defective relief valve - or
Defective suction guage.
It doen'nt mention the drive coupling - but that is also a great suggestion..

Let us know what you find!