DRIVELINE VIBRATION/NOISE DIAG. (ELECT. VIB. ANALYZER)

SUBJECT: DRIVELINE VIBRATION AND NOISE

MODEL and YEAR: 1985-92 M VANS 1990-92 L VANS

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 92-190B-4A, DATED SEPT. 1992. THE LABOR OPERATION NUMBERS HAVE BEEN CORRECTED. ALL COPIES OF 92-190A-4A SHOULD BE DISCARDED.

Various concerns related to vehicle vibration in 1985-1992 M/L vans have been studied and analyzed. Contributors to vibration can come from the engine, driveline, or wheel/tire systems which makes an accurate diagnosis difficult.

To aid the service technician with a systematic approach to diagnosis and correction, GM service worked with Kent Moore to develop and release the Electronic Vibration Analyzer (EVA) (J 38792). By using EVA on a road test, the technician now has the ability to use the frequency of the vibration to identify the source of the vibration. This tool, along with a complete understanding of the STG Vibration Correction booklet 13002.02 dated August 1990, is necessary in determining the cause and correction of vibration conditions in a vehicle. The EVA tool is available through Chevrolet Motor Division's Tool Loaner Program as outlined in R. W. Starr's letter to all dealers dated January 24, 1992, Subject: Chevrolet Service Tool Loaner Pilot Program, the procedure of which is attached. You may also call Kent Moore's toll free number (1-800-345-2233) for complete details. The tool is shipped on consignment with an instruction manual, STG Vibration Correction Booklet and Tire Rotational Order Charts.

GM service has made available a program for the dealers to address disturbances by installing "qualified components" into a problem vehicle. These qualified parts are:

a. Tires

b. Front propshaft (L vans)

c. Rear propshafts (M/L vans)

d. Tuned damper, rear axle pinion nose

These parts can only be obtained by establishing a case with Chevrolet Technical Assistance. To identify the correct system, it is important that the technician follow the flow chart contained in this bulletin (Figure 1 for M Van and Figure 2 for L Van) to obtain the necessary vibration frequencies prior to calling the Technical Assistance Network. Chevrolet Technical Assistance will then authorize shipment of the needed part(s) to your dealership.

SERVICE PROCEDURE:

1. Road test the vehicle on a smooth surface (preferably asphalt). Use the Electronic Vibration Analyzer (EVA) (J 38792) to obtain the frequencies/RPM's at points of disturbance. A passenger should be present during the road test to read and record the information.

2. Use the recorded frequencies/RPM's from the road test to fill in the information on Figure 3.

3. Follow the EVA BALANCE PROCEDURES below to reduce the vibration complaint.

EVA BALANCE PROCEDURES

1. Raise the vehicle on a hoist and support it with safety stands. Support the rear axle at the outer most part of the axle tube. Keep the vehicle supported at curb height.

2. For reference, mark the propshaft at 90 degree intervals (four locations) with white paint or chalk. These marks will be used for the strobing function.

3. L-vans only: remove the front propshaft.

4. M/L vans: remove the rear tire/wheel assemblies and brake drums.

5. Inspect the propshaft and U-joints for undercoating. If undercoating is present, it must be removed.

6. Measure the runout on the rear propshaft and companion flange. There must be no more than 0.025 in. (0.63 mm) runout on the rear propshaft and no more than 0.015 in. (0.38 mm) runout on the companion flange.

7. Inspect the rear propshaft and U-joints for any possible damage.

8. If the runout IS UNACCEPTABLE AND/OR THERE IS DAMAGE, call Chevrolet Technical Assistance for further instructions.

If the runout IS ACCEPTABLE AND THERE IS NO DAMAGE:

a. Use EVA to system balance the rear propshaft to the rear axle by attaching the accelerometer to the bottom of the pinion nose with the word "UP" facing UP.

b. Clip the inductive pickup of an inductive type timing light to EVA's timing light loop and connect the timing light to a 12 volt source.

c. System balance the rear propshaft to the rear axle using the instructions contained in the Electronic Vibration Analyzer Manual in Appendix Three.

CAUTION:

DO NOT USE THE CRUISE CONTROL TO MAINTAIN A STEADY SPEED.

Important: DO NOT depress the brake pedal with the rear brake drums removed.

9. Road test the vehicle. If the vibration is not noticeable, the vehicle is repaired. If the vibration is still present, contact Chevrolet Technical Assistance for further instructions.

WARRANTY INFORMATION:

For vehicles repaired under warranty use:

Labor Op. Description Labor Time --------- ----------- ---------- T1860 Road Test Actual Time up to 0.9 hrs.(*)

T7338 Rear Propshaft Runout Check 0.2 hrs.

T7339 System Balance 0.7 hrs.

(*)For proper claims documentation, refer to the Claims Processing Manual.

TOOL LOANER PROCEDURE

o Dealer calls Kent-Moore's toll free phone number 1-800-345-2233.

o Dealer states desire to be sent J 38792-CL Vibration Analyzer as a loaner.

o Tool order initiated by Order Department and processed through regular business.

o Tool shipment to be made via "UPS Ground Service", but at request of dealer will be made via "Overnight Express" (at dealer's expense).

o Tool sent to dealer in protective padding in reusable cardboard shipping carton. Carton specially marked to denote loaner tool enclosed and advises that carton be retained for return shipment. Return address with prepaid postage included.

o Tool includes descriptive operating and diagnostic instructions.

o Literature instructing dealer on return procedure and optional purchase of tool is included in carton.

o Initial loan period is five business days. Extensions are available in two day increments by calling Kent-Moore Customer Service at 1-800-345- 2233. A maximum of two extensions allowed (unless extenuating circumstances are involved).

o Loan period to start at anticipated date of dealer receipt of tool (three day grace period allowed for shipping).

o Dealer has option to purchase loaner analyzer at discounted price (1992 catalog price: $995, option to purchase price: $695).

o Returned tools are inspected for damaged or missing parts by Kent-Moore Returned Goods Department. In the event a tool is damaged during use, Customer Service is notified of damaged or missing parts and then assesses cost of repairs. Kent-Moore Customer Service calls dealership Service Manager to advise of forthcoming parts account invoice for repair charges. Kent-Moore, Accounting notifies Chevrolet Dealer Accounting of repair charges. Dealer parts account is invoiced accordingly by Chevrolet.

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.