Steering Wheel - Highway Speed Vibration
86subaru1NUMBER 05-19-86
APPLICABILITY: ALL 1985-86 VEHICLES DATE 03-11-86
SUBJECT: Steering Wheel Vibration or "Flutter"
This bulletin has been prepared to assist in the diagnosis and repair of steering wheel vibration or "flutter". This "flutter" is defined as a rapid left to right pulsation of the steering wheel at speeds of 55 to 65 mph on a smooth road surface. It may be accompanied by a "body shake" or vibration in the seat and/or floor at these same speeds. Our investigations have shown that vibrations in the body and steering can be caused by several conditions. However, the single major cause of steering wheel flutter has been wheel imbalance. Steering wheel flutter and accompanying body vibrations can be eliminated through careful vehicle servicing.
PROCEDURE:
1) When this condition is encountered, and verified through a road test, it must be confirmed that all contributing factors have been inspected and repaired as necessary. Items such as wheel bearings, shock absorbers, universal joints, DOJ and CVJ must be in proper operating condition. Rotating parts must be free of rustproofing and/or mud.
2) Next, determine if the vehicle is fitted with the modified steering rack sleeve spring. If not, replace the spring as necessary.
There is an obvious difference in the wire diameter used in the old coil spring compared to the modified ones. The new springs are thicker than the old ones. Actual wire diameters are:
ORIGINAL MODIFIED
Manual Steering - CGR 0.25 cm (0.10 in.) 0.33 cm (0.132 in.)
Power Steering 0.19 cm (0.076 in.) 0.25 cm (0.10 in.)
STEERING RACK SLEEVE SPRING TENSION INCREASE
Starting VIN's:
Sedan 235 157
Station Wagon 449 009 March, 1985 Production
XT Coupe 304 233
PART NUMBERS OF MODIFIED PARTS
S/W and 4-Door Sedan XT Coupe
Power Steering 31263GA760
31260GA291
Manual Steering-CGR 31248GA080 31248GA080
FIGURE 1:
3) All 1985-86 vehicles are fitted with tires marked for radial force variation. Radial force variation (RFV) of a tire is a measurement of the difference in radial runout measured as a force of the tire against a drum. (See Figure 1).
The highest point of radial force variation is noted by a red paint mark on the tire.
OEM Subaru wheels are marked with a gray paint spot at the point of minimum radial runout. To obtain the minimum RFV of a tire and wheel assembly, the maximum RFV of a tire is matched to the point of minimum radial runout of the wheel. An inaccuracy in the RFV matching can be observed as an excessive radial runout of the tire and wheel assembly when rotated on a constant axis. Radial runout of the tire and wheel assembly, measured at the tire tread, should be less than 2.0 mm.
FIGURE 2:
If this inaccuracy is encountered, it can easily be corrected by measuring the radial runout of the wheel (See Figure 2), with a dial indicator and determining the minimum point. This point should then be matched to the red dot on the tire.
Measurement of the actual radial rim runout can be performed at this time using this dial indicator mounting.
NOTE: Maximum acceptable wheel radial runout is 1.0 mm (0.039 in).
4) Once this satisfactory RFV matching has been achieved, the next step is an accurate balancing of the wheels. We cannot over emphasize the necessity for accurate wheel balancing.
FIGURE 3:
The minimum equipment that a dealer should have is an electronic off the car spin balancer. Either stud mount or cone mount adapters are acceptable, but we have found that many stud mount adapters cause the machine to be out of calibration. If a stud mount adapter is used, the non-adjustable type is less likely to contribute to machine inaccuracy. The recommended procedure for mounting a wheel assembly on a balancer is shown in figure 3.
A quick and easy test of machine accuracy can be accomplished by first spinning and balancing a wheel and tire assembly. Next, rotate the tire and wheel assembly by 180~ on the balancer axle. Take care not to reposition the mounting cone, if this is the type of adapter used, then re-spin. If the machine shows the wheel and tire to be out of balance, the machine is inaccurate and must be recalibrated.
The vehicle can now be road tested and its performance compared to that observed during the pre-repair road test.
In most cases, steering "flutter" and resultant body vibration will have now been eliminated. In extreme cases, however, if "flutter" still exists it is recommended at this point to perform a "finish" on the car wheel balancing.
One additional change which FHI has made in production is a modification to increase the dampening ability of the leading rod bushings.
Starting VIN's Using Modified Bushings Are Listed Below:
1986 MODEL YEAR
Sedan 206 675
Station Wagon 408 600 September, 1985 Production
XT Coupe 302 506
Part number for a modified bushing is 21047GA312.
The installation of these bushings to decrease driveline residual vibration should be made, if necessary, only after the procedures described in this bulletin have been performed in the order presented. Their main function is to decrease the transmission of vibration from road irregularities to the passenger compartment.