VIBRATION DIAGNOSIS USING A REED TACH. & ROTATIONAL CHARTS

Cadillac has developed rotational order charts to provide a systematic method for diagnosing vibration conditions when used with a resonant reed tachometer. Refer to Service Bulletin T-86-4, Group 0, for background and use of rotational order charts and reed tachometers. This bulletin provides an update on reed tachometer availability and 1990 model rotational order chart information.

Resonant Reed Tachometer:

Reed tachometers may be purchased from Biddle Instruments at the following address:

Biddle Instruments 510 Township Line Road Blue Bell, PA 19422 Telephone: (215) 646-9200

"We believe this source and their equipment to be reliable. There may be additional manufacturers of such equipment. General Motors does not endorse, indicate any preference for, or assume any responsibility for the products or equipment from these firms or for any such items which may be available from other sources."

Biddle no longer offers a reed tachometer scaled in Hertz (Hz) but does offer a faceplate scaled in Hertz to be used with a reed tachometer that is scaled in revolutions per minute (rpm). Orders should include the following information:

Catalog Description Number Price*

FRAHM T-72 resonant reed tachometer scaled in rpm 313510 $670.00 Faceplate for FRAHM T-72 scaled in Hz 5220-40 $5.00 * - Approximate price at time of publication.

Rotational Order Charts:

This bulletin includes a rotational order chart for 1990 Broughams equipped with the trailer towing package (3.08 rear axle ratio). For base model 1990 Broughams (2.73 rear axle ratio), use the rotational order chart for 1986-1987 Broughams in Service Bulletin T-87-104, Group 0. For 1990 Broughams with the D'Elegance option (2.93 rear axle ratio) and the 1990 Eldorado, Seville, STS, and Allante use the rotational order chart for the corresponding 1989 model in Service Bulletin T-89-106, Group 0.

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.