M/T - Cyclic Droning Noise
90isuzu05 BULLETIN NUMBER SB90-05-005ISSUE DATE November 8, 1990
GROUP TRANSMISSION
TROOPER II (KT) MUA CYCLIC DRONING NOISE
AFFECTED VEHICLES
Trooper II (KT) models equipped with MUA manual transmission.
SERVICE INFORMATION
Affected vehicles may experience a cyclic (harmonic, varying level) droning noise when traveling at steady throttle at 45-50 mph in 4th or 5th gear. The noise may be caused by an improperly adjusted driveline angle, improperly balanced transfer case countershaft, or worn transfer case countershaft bearings.
This Service Bulletin contains procedures for eliminating the noise by adjusting the driveline angle and/or replacing the countershaft and countershaft bearings.
Figure 1:
SERVICE PROCEDURE
1. Check the driveline angle as follows:
NOTE:
Ensure that the vehicle is level, in order to obtain an accurate driveline angle reading.
a. Measure the vehicle angle by using a magnetic base universal protractor attached to the frame rail. Record this reading.
b. Place the protractor on the front propeller shaft behind the transmission (Figure 1). Record this reading.
c. Subtract the first reading (frame rail) from the second reading (propeller shaft), to obtain the driveline angle. Driveline angle should be no greater than 5 degrees +/- 1/2 degree.
2. If driveline angle is greater than 5 degrees +/- 1/2 degree, install a shim (listed in the "Parts information" section of this Service Bulletin) between the vehicle frame and transmission crossmember, on both sides of the vehicle, as follows (Figure 1):
a. Support the transmission, using appropriate transmission hoist.
b. Remove the skid plate.
c. Remove eight bolts securing the transmission crossmember to the frame.
d. Install a shim between the frame and the transmission crossmember.
e. Reinstall eight bolts to secure the transmission crossmember to the frame. Torque bolts to 45-67 ft. lbs. (6.2-9.3 kg/m).
f. Reinstall skid plate. Torque four fixing bolts to 20-34 ft. lbs. (2.8-4.7 kg/m).
3. Test drive vehicle and note any cyclic droning noise in 4th or 5th gear. If noise continues, replace the transfer case countershaft and countershaft bearings as follows.
4. Remove the transfer case countershaft as described in the appropriate Workshop Manual.
5. Examine the bearings supporting the countershaft. If they have an unusual wear pattern, replace the bearings, using those listed in the "Parts Information" section of this Service Bulletin.
6. Install a new balanced countershaft, as described in the appropriate Workshop Manual. See the "Parts Information" section of this Service Bulletin.
PARTS INFORMATION
Part No. Description Quantity
Required
8-97025-119-0 Balanced Countershaft 1
8-94422-054-0 Rear Output Shaft Bearing (Front) 1
8-94422-050-0 Countergear Bearing (Front) 1
8-94422-058-1 Countergear Bearing (Rear) 1
8-94325-131-0 Shim 2
FLAT RATE MANUAL UPDATE INFORMATION
OPERATION ADDITIONAL
OPERATION NUMBER TASK TIME INSTRUCTIONS
Countershaft 050575 Replace 4.0 Includes: 050595 R&R Transmission
Includes: Replace bearings if necessary
Includes: 115107 Adjust Driveline Angle
Driveline Angle 115107 Adjust 1.0 Includes: R&R skid plate and
crossmember
Includes: Install shim on both sides