Steering Shimmy - Diagnostic Procedure
Article No.96-7-20
03/25/96
STEERING - SHIMMY - DIAGNOSTIC PROCEDURE - F-350 (4X4), F-SUPER DUTY AND CHASSIS CAB (F-47) VEHICLES
LIGHT TRUCK:
1988-96 F SUPER DUTY, F-350, F-47
This TSB is being republished in its entirety to include 1992-96 model year vehicles.
ISSUE:
Front end shimmy may occur at various driving speeds and is usually induced when hitting bumps such as large potholes or rough railroad crossings. Shimmy is not always verified during the road test.
ACTION:
Check all the systems that can cause shimmy. After a general review of the front suspension and steering systems, make the necessary adjustments as noted in the following diagnostic procedure. The review should include bolt and nut torques to insure they are to specified torques. When encountering excessively worn tires, shackle bushings and out-of-balance wheel or tire assemblies. Refer to the 1991 Light Truck Service Manual, Pages 04-00-7 and the inspection procedures beginning on Page 04-00-8.
NOTE:
FOR INFORMATION ON F-SUPER DUTY MOTORHOME CHASSIS (F-53), SEE TSB 90-23-12.
Shimmy as observed by the driver is defined as large amplitude, rotational oscillations of the steering wheel resulting from large, side-to-side (lateral) tire/wheel movements. Shimmy should not be confused with nibble, a condition resulting from the tire interaction with various road surfaces and observed by the driver as small amplitude, rotational oscillations of the steering wheel. To diagnose nibble and other vibrations, which are sometimes confused with shimmy, such as steering column shake, wheel/tire imbalance, consult the Noise/Vibration/Harshness (NVH) diagnostic, Brake NVH and Tire NVH sections in the Light Truck Service Manuals.
The following items will contribute to the "shimmy" condition and should be inspected and repaired as required to assure the total repair effectiveness. After all components have been reviewed and repaired, install the appropriate steering damper kit.
STEERING LINKAGE
With the vehicle weight on the front wheels, observe the steering linkage joints while someone else turns the vehicle steering wheel from side-to-side.
^ (RBS) RUBBER BALL SOCKET LINKAGE
Observe if the ball stud makes contact with the window opening in the socket bowl, refer to Figure 1. Then remove the linkage and determine if the rubber is torn. If contact is made with the window opening or the rubber is torn, replace with a greaseable, steel socket. Refer to Figure 2 for applicable replacement parts.
^ (GREASEABLE) STEEL LINKAGE
For steel (greaseable) joints, measure and observe lateral (side-to-side) lash in the joint. If the lash exceeds 1.5 mm (0.060"), the joint should be replaced. Refer to Figure 3. With the linkage removed, check the vertical end play. If the end play is greater than 2.3 mm (0.090"), replace the joint, Figure 3. Also, determine if the steel joint spins freely. If the joint spins freely by hand, the joint should be replaced. Refer to Figure 2 for applicable replacement parts.
STEERING GEAR AND FRAME
Inspect the mounting surface of the gear and the mounting area of the frame, shown in Figure 4, for signs of motion, for loose rivets, and for cracks. Removal of the gear from the frame may be required. All damages must be repaired. Refer to the Light Truck Service Manual, Section 02-01 for service procedures.
INSPECT THE FRAME IN THE FOLLOWING AREAS:
^ Frame rail near the steering gear top and bottom flanges
^ Frame rail at the steering bolt heads
^ Frame rail at or near the leaf spring mounting brackets
^ Front crossmember where the track bar mounting bracket mounts
If shimmy has been experienced, replace the steering gear sector shaft with repair kit (EOAZ-3575-A) as outlined in the 1991 Light Truck Service Manual.
Check the steering gear for presence of meshload. With the front wheels off the ground, hold the tire and turn the tire side-to-side slowly. The effort should increase when turning the tire straight ahead. If no increase in effort is noted, perform the Service Manual procedure as outlined on Page 11-020-06 in Volume 1 of the 1991 Light Truck Service Manual to check and adjust the meshload.
BALL JOINTS OR WORN KING PIN
For proper diagnosis and replacement of king pins and ball joints, refer to the 1991 Light Truck Service Manual, Volume 1, Page 04-00-09.
WHEEL BEARING END PLAY
For proper diagnosis, adjustment or replacement of the wheel bearing, refer to the 1991 Light Truck Service Manual, Volume 1, Pages 04-00-09 and 04-01 A-5.
ALIGNMENT
All alignment adjustments should be measured and set to the recommended specifications as stated in the 1991 Light Truck Service Manual, Volume 1, Page 04-00-13.
WHEEL/TIRE SIZE AND BALANCE
Compare tire size and wheel size with sizes and pressures on the certification label. Inflate to the specified pressure. Assure correct balance of the front wheels.
STEERING DAMPER
A steering damper kit should be installed when shimmy is experienced. Install the following Service Kits: F-350 4X4 SRW and DRW vehicles (E7TZ-3E651-C); F-Super Duty Chassis Cab (F-47) (E8TZ-3E651-B). Steering damper installation sketches are shown in the 1991 Light Truck Service Manual, Volume 1, Section 04-00, Pages 8 and 10.
Install the mounting brackets and the damper as shown in Figures 5, 6, and 7.
1. When locating the mounting bracket on the steering linkage, turn the wheels to either a full LH or RH lock position.
2. Locate the mounting bracket so the damper has approximately an additional 12.7 mm (0.5") of travel before the damper's maximum amount of travel, as shown in Figure 5.
3. Turn the wheels to the opposite lock position and check the damper travel to ensure the maximum amount of travel has not been reached. The damper should not prevent the wheels from reaching their lock-to-lock turning positions.
4. Tighten all bolts as shown in Figures 6 and 7, depending on which vehicle you are repairing.
ROAD TEST
After repairs or adjustments have been made, road test the vehicle to ensure that shimmy it' not present.
Parts Block
OTHER APPLICABLE ARTICLES: 90-23-12
SUPERSEDES: 92-4-11
WARRANTY STATUS: Eligible Under Basic Warranty Coverage
OPERATION DESCRIPTION TIME
960720A Inspect Steering Linkage, 0.6 Hr.
Frame Ball Joints Or King Pins
960720B Replace Tie Rod, Tie Rod 0.3 Hr.
End And/Or Drag Link
Assembly - One Or Two
960720C Replace Tie Rod, Tie Rod 0.5 Hr.
End And/Or Drag Link
Assembly - Three Or More
960720D Inspect Wheel Bearing End 0.2 Hr.
Play And Presence Of
Steering Gear Meshload
960720E Adjust Both Front Wheel 0.5 Hr.
Bearings
960720F Adjust Steering Gear Only 0.4 Hr.
- In Chassis
960720G Replace Steering Gear 1.3 Hrs.
Sector Shaft
960720H Check Front Tire Balance 0.6 Hr.
960720I Check Tire Size And 0.8 Hr.
Pressure, Measure
Alignment Settings
960720J Reset Alignment To 0.9 Hr.
Specifications
960720K Install Steering Damper Kit 0.6 Hr.
DEALER CODING
CONDITION
BASIC PART NO. CODE
3E651 33
OASIS CODES: 303000, 304000, 306000