CAMPAIGN-FLEX PLATE CRACKING (INSPECT/REPAIR PROC.)
Subject: AUTOMATIC TRANSMISSION FLEX PLATE CRACKING
Models: Certain 1991 B6/C5-7H With Gasoline Engines (RPO LR0 and LS0)
General Motors of Canada has determined that certain 1991 GMC School Bus Chassis and C5-7H TopKick medium duty trucks equipped with 6.0L (LR0) or 7.0L (LS0) gasoline engines and AT545 Allison automatic transmissions may exhibit cracking of the flex plate around the bolt circle where it attaches to the crankshaft. The cracking results from excessive stress induced by the misalignment of the transmission centerline with the crankshaft centerline. The misalignment is caused by improper machining or the flywheel housing. The cracking will be made apparent by a noise noticeable to the driver. Eventually, if the noise were to go unheeded, the flex plate will completely separate from the crankshaft resulting in loss of power to the driveline and/or possible transmission damage.
To correct this condition, dealers will check the flywheel housing for eccentricity and replace the housing and flex plate as necessary.
VEHICLES INVOLVED:
Involved are certain 1991 GMC B6 School Busses and C5-7H TopKick medium duty trucks equipped with 6.0L and 7.0L gasoline engines and AT545 Allison automatic transmissions built within the following VIN breakpoints:
Make Model From Through ---- ------- -------- -------- GMC TopKick MJ500018 MJ520954 GMC B6 Bus MV500001 MV501905
All affected vehicles have been identified by the VIN listing provided to involved dealers with this bulletin. Any dealer not receiving a listing was not shipped any of the affected vehicles.
DEALER CAMPAIGN RESPONSIBILITY:
Dealers are to service all vehicles subject to this campaign at no charge to owners, regardless of mileage, age of vehicle, or ownership, from this time forward.
Whenever a vehicle subject to this campaign is taken into your new or used vehicle inventory, or it is in your dealership for service in the future, you should take the steps necessary to be sure the campaign correction has been made before reselling or releasing the vehicle.
Owners of vehicles recently sold from your new vehicle inventory are to be contacted by the dealer, and arrangements made to make the required modification according to instructions contained in this bulletin.
CAMPAIGN PROCEDURE:
Refer to Section 4 of the Service Policies and Procedures Manual for the detailed procedure on handling Product Campaigns. Dealers are requested to complete the campaign on all transfers as soon as possible.
OWNER NOTIFICATION:
All owners of record at the time of campaign release are shown on the attached computer listing and have been notified by first class mail from General Motors. The listings provided are for campaign activity only and should not be used for any other purpose.
PARTS INFORMATION:
Parts required to complete this campaign should be ordered through regular channels, as follows:
Part Number Description Quantity/Vehicle ----------- ------------ ---------------- 15647398 Housing 1 10114196 Flex Plate 1 462619 Retainer 2
PARTS AND LABOUR CLAIM INFORMATION:
Credit for the campaign work performed will be paid upon receipt of a properly completed campaign claim card or DCS transmission in accordance with the following:
Repair Code Description Time Allowance ----------- ------------------------ -------------- 2A C5-7H R&R Flywheel (Flexplate) 3.6 Hrs. and Measure Eccentricity (within specs)
3A C5-7H R&R Flywheel (Flexplate) 4.0 Hrs. and Measure Eccentricity (not within specs)
4A B6 R&R Flywheel (Flexplate) 4.3 Hrs. and Measure Eccentricity (within specs) 5A B6 R&R Flywheel (Flexplate 4.9 Hrs. and Measure Eccentricity (not within specs)
Time allowance includes 0.1 hour for dealer administrative detail associated with this campaign. Repair codes 2A, 3A, 4A and 5A include $5.95 for 2 litres of Dexron II Automatic Transmission Fluid (part number 993296). Parts credit will be based on dealer net plus 30% to cover parts handling.
SERVICE PROCEDURE:
REMOVAL
1. Block rear wheels.
2. On School Bus only: remove transmission access cover from floor of vehicle.
3. Remove negative (-) battery cable from battery.
4. Raise and support front axle.
5. Drain transmission oil.
6. Disconnect prop shaft at transmission, centre support and on school bus only, disconnect the two (2) safety loops.
7. Disconnect dipstick.
8. Disconnect electrical, vacuum, shift linkage connections, and on school bus only, speedometer cable connection.
9. Disconnect transmission cooler lines and retainers.
10. Disconnect parking brake cable and bracket.
11. Unfasten the starter motor from the flywheel housing.
12. Remove access cover from the bell housing.
13. Disconnect the torque converter fasteners.
14. Install transmission jack and support transmission while removing engine mount fasteners.
15. Support rear of engine and remove the transmission case fasteners.
16. Remove transmission.
17. Remove flywheel fasteners and flywheel (flex plate).
18. Perform measurement of eccentricity of the flywheel housing using a dial indicator, refer to Figure 1.
Note: If the flywheel housing is within specifications, continue to INSTALLATION procedures. If the flywheel housing is NOT within specifications, continue to Step 19.
19. Remove flywheel housing fasteners and flywheel housing from engine.
20. Transfer parts from the old flywheel housing to the new flywheel housing.
FIGURE 1 - (The following text is associated with figure 1)
MEASUREMENT OF THE ECCENTRICITY OF THE FLYWHEEL HOUSING BORE USING A DIAL INDICATOR
SECURELY FASTEN THE BASE OF THE DIAL INDICATOR SUPPORT EXTENSION TO THE CRANKSHAFT HUB. ROTATE THE CRANK SHAFT SO THAT THE DIAL INDICATOR WILL SWEEP THE ENTIRE FLYWHEEL HOUSING BORE. RECORD THE MAXIMUM AND MINIMUM READINGS. THE DIFFERENCE IN THESE READINGS SHOULD NOT BE GREATER THAN THE TOLERANCES SPECIFIED BELOW.
AT 500
FLYWHEEL HOUSING: 16.125 +0.005 IN. BORE DIAMETER -0.000
(409.58 +0.13 mm) -0.00
BORE ECCENTRICITY (LIMITS ARE 0.020 IN. T.I.R. FOR INSTALLED ENGINES.) (0.51 mm)
INSTALLATION
1. Install the flywheel housing and fasteners. Torque the fasteners to 45 N.m. (33 lbs. ft.).
2. Install flywheel (flex plate) and fasteners, torque the fasteners to 90 N.m. (65 lbs. ft.).
3. Install transmission, align, install fasteners, torque the fasteners to 48 N.m. (35 lbs. ft.).
4. Install the rear engine mount fasteners, torque them to 196 N.m. (145 lbs. ft.). Remove support and transmission jack.
5. Install torque converter fasteners, torque to 56 N.m. (41 lbs. ft.).
6. Install access cover to transmission bell housing.
7. Connect starter motor to flywheel housing, torque to 37 N.m. (27 lbs. ft.).
8. Connect transmission cooler fines and retainers.
9. Connect electrical, vacuum, shift linkage connectors and on school bus only, speedometer cable connection.
10. Connect dipstick.
11. Connect parking brake cable and bracket.
12. Connect centre support, prop shaft and on school bus only, 2 safety loops.
13. Remove supports and lower vehicle.
14. School Bus only: install transmission access cover at floor of vehicle.
15. Connect negative (-) battery cable on battery.
16. Fill transmission with new transmission fluid (P/N 993296) to proper level.
17. Remove blocks from rear wheels.
18. Install "Campaign Identification Label".
INSTALLATION OF CAMPAIGN IDENTIFICATION LABEL
Clean surface of radiator upper mounting panel and apply a Campaign Identification Label. Make sure the correct campaign number is inserted on the label. This will indicate that the campaign has been completed.
Dear General Motors Customer.
Our records show that you own one of our 1991 model General Motors GMC B6 School Bus Chassis or TopKick medium trucks. The rate at which these trucks have been accepted into the stream of commerce has been very gratifying to us. In addition, feedback from customers, dealers and our own tracking systems indicate a very high degree of product reliability thus far.
We have recently become aware of a situation on certain 1991 GMC B6 School Bus Chassis and TopKick with a specific transmission which may reduce your truck's reliability. The flywheel housing of certain vehicles was machined improperly causing excessive stress in the housing. The stress causes cracking of the housing due to misalignment of the transmission centerline with the engine crankshaft centerline. The cracking will manifest itself by a noise noticeable to the driver. Eventually, if this noise goes unheeded, the flex plate win completely separate from the crankshaft resulting in loss of power to the driveline and/or possible transmission damage.
In the interest of maintaining your truck's reliability, we would like to correct this condition by checking the flywheel housing for eccentricity and replacing the housing and flex plate if required.
Please contact your GM dealer as soon as possible to arrange a service date.
If parts are required, ask your dealer for details regarding their availability. If parts are not in stock, they can be ordered before scheduling your service date.
This letter identifies your vehicle. Presentation of this letter to your dealer will assist their Service personnel in completing the necessary correction to your vehicle in the shortest possible time.
Subsequent to contacting your dealer, further assistance, if required, may be obtained from our Customer Assistance Centre, toll free, by calling 1-800-263-3777 (English), or 1-800-263-7854 (French).
We are sorry to cause you this inconvenience; however, we have taken this action in the interest of your continued satisfaction with our products.
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.
