PL720 2WD L4-2488cc 2.5L DSL (SD25) (1985)
Technical Service Bulletin # TS85096
Date: 850827
Driveline - High/Low Speed Vibration
TS85-096
August 27, 1985
Propeller Shaft & Differential
DRIVELINE VIBRATION, 4X4 TRUCK
APPLIED MODEL
1983.5 - 1986 4x4 720 Truck
SERVICE INFORMATION
Some 4X4 Trucks may exhibit a vibration at two different speed ranges.
A.
HIGH SPEED VIBRATION
The high speed vibration, which may be accompanied by booming noise, occurs at 50-60 MPH. This vibration can be described as a continuous
buzz in the seat, steering wheel and floor. A rapidly vibrating transfer case lever may also indicate driveline imbalance.
B.
LOW SPEED VIBRATION
The low speed vibration occurs at 20-40 MPH. The low speed vibration is similar to the high speed, but with less intensity. Vibration caused by tire
imbalance resembles a shaking sensation and should not be confused with driveline vibration. Additional vibration may be caused by having the
transfer case in the 4H position or the 2H position with the hubs locked.
Use the following Service Procedure to reduce driveline vibration in incident vehicles. This procedure incorporates portions of, and replaces, the
previous driveline vibration bulletin PD84-001 (TS84-001).
NOTE:
Any testing or high speed evaluation should be done with the transfer case lever in the 2H position and the hubs unlocked.
Service Procedure
A.
HIGH SPEED VIBRATION (50 - 60 MPH)
1.
Road test the vehicle between 50 and 60 MPH to determine the speed at which the vibration is most noticeable. Record this speed.
2.
Support vehicle on an axle hoist at points suitable for a safety stand (Figure 1).
3.
Remove both rear tire/wheel assemblies and securely install two (2) nuts to each brake drum (opposite studs) to hold brake drums on axle
(Figure 2).
4.
With the engine running, place the gear shift lever into fifth gear and have one person slowly bring the indicated speed to that speed noted in
Step 1 (or the worst condition speed in the 50-60 MPH range). EXTREME CAUTION should be exercised at this point due to all the rotating
surfaces. Stand clear of the rotating brake drums and driveshafts.