1968 Corvette: Service Bulletin: Delcotron Noise (Moan)
Subject: Delcotron Noise (Moan)
Model and Year: 1968 Passenger Cars Equipped with V-8 Engines and Delcotron High Speed Fan
Source: Chevrolet Technical Service Bulletin
Bulletin No: 68-T-63
Date: Sept. 13, 1968
TO: ALL CHEVROLET DEALERS
Complaints of Delcotron noise (moan) have been reported from the field on 1968 passenger cars equipped with V-8 engines. The majority of complaint vehicles were equipped with the Delcotron high speed fan, #1969448, which was found to be dynamically unbalanced.
If the above complaint is encountered, the installation of the base fan, #1966990, will reduce the noise to an acceptable level.
Engineering has released an interim change to cancel #1969448 and replace it with #1966990 for V-8 and Mark engines with air conditioning.
Delcotron noise is most commonly detected under road load or neutral run-up in the range of 2000-2600 R.P.M. The vibration period that creates the Delcotron "boom" or "moan" can be felt by place the hand on the Delcotron frame and running the engine speed up in neutral to the critical speed.
On complaint vehicles in the field, the engine timing specifications, plugs and points should be checked first to assure engine performance is normal before replacing the fan.
PARTS AND LABOR DATA
Part No: 1966990
Part Description: Fan - Delcotron
Chevrolet Motor Division
General Motors Corporation