Water pump service package no. 556283 available from WDDGM, now contains a pump with a sheet metal impeller. This pump is also being used on production engines.
Dealer Bulletin 80-I-86, Group 60, Number 21 issued March, 1980 defined criteria for a cast iron impeller. It stated it must have square vanes and a maximum of .045 inch clearance. It is no longer necessary to be concerned about these items if a new pump with the sheet metal impeller is used.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.