Excessive Steering Wheel Shimmy Or Chassis Vibration (JA02922)

EXCESSIVE STEERING WHEEL SHIMMY OR CHASSIS VIBRATION

TECHNICAL SERVICE BULLETIN

AFFECTED VEHICLES

General Information

INTRODUCTION

Do you have a vehicle with a steering wheel shimmy or chassis vibration that you feel at highway speeds and you know it is not  a normal characteristic of the vehicle? Many things can cause this problem, for example:

• Out-of-balance tires, rims, front wheel hubs, or front brake discs
• Wrong tire pressures
• Tire(s) that are not fully seated on the rim(s)
• Excessive tire runout under load
• Damaged tires (cuts, missing rubber, etc.)
• Use of aftermarket parts (tires, rims, steering components, or suspension components)
• Damage

This job aid looks at the entire issue of steering wheel shimmy and chassis vibration and what it takes to fix the problem. It includes these topics:

• Test-Driving the Vehicle
• Interpreting the Vibration
• Understanding Phase Matching
• Balancing the Wheels
• Matching the Wheels to the Hubs
• Calibrating the Wheel Balancer
• Reading Tire/Rim Runout with a Hunter GSP9700 Wheel Balancer

TEST-DRIVING THE VEHICLE

Follow these steps and answer the questions in the order they are asked. If possible, have someone along to record your answers.

1. Test-drive the vehicle exactly as described on your RO.
2. Describe the vibration.
   NOTE: If the vibration is caused by something other than the wheels (transmission, engine, exhaust, etc.), end your test-drive right now. Check SIS for applicable service information.
   • Where do you feel the vibration is coming from? 
   • Does the vibration go away after a few minutes of driving? Does it come and go? 
   • Does the steering wheel shimmy? (It feels like it is shaking left and right.) 
3. Slow down until the vibration goes away. Now, speed up in 5 mph  increments, holding that speed for 15 seconds  or more before speeding up again. At what speed do you start to feel the vibration again? As you continue speeding up, does the vibration get stronger, weaker, or does it just stay the same? 
4. Drive for about 2 miles  on straight and curved roads at the speed where you felt the vibration strongest in step 3.
   • When driving straight ahead, is the vibration constant or does it come and go? 
   • When following a curve, is the vibration constant or does it come and go? 
5. Shift into Neutral. Does the vibration go away?
6. Drive under the conditions that you feel the vibration the most. Speed up, applying different foot pressure to the accelerator pedal (gentle, medium, and hard). Does the vibration stay the same or is there a specific foot pressure where it changes? 
7. Climb a hill at a steady speed. Does the vibration stay the same or does it get stronger as you climb? Apply different pressures like you did in step 6. Does the vibration stay the same or does it get stronger when you apply a particular foot pressure? 
8. Test-drive a known-good vehicle that is the same model, year, and trim level as your customer's vehicle and is completely stock. Drive it exactly as you did in steps 2 thru 7. Now, compare your two test-drives.
   • If your customer's vehicle is similar or better than the known-good vehicle, the vibration is a normal characteristic of the vehicle.
   • If your customer's vehicle is noticeably worse than the known-good vehicle, you need to interpret the vibration before moving ahead.

INTERPRETING THE VIBRATION

UNDERSTANDING PHASE MATCHING

The most critical speed for tire-induced vibration is from 55 to 65 mph  . At those speeds, a tire spins at a rate of anywhere from 10 to 15 times per second  .

When two out-of-balance tires are spinning so their heavy spots hit the road at different times  , they are said to be out of phase  and, at a certain point, their vibrations can actually cancel each other out. But if both tires are spinning so their heavy spots are now hitting the road at the same time  , they are said to be in phase  and their vibrations can actually add together.

When those vibrations cancel each other out, you get steering wheel shimmy. When they add together, you get chassis vibration (floorboard shake), although in some vehicles, the steering wheel can be more sensitive than the floor.

As the tires continually come into and out of phase, the steering wheel shimmy continually comes and goes. You feel it increase, reach a peak, then diminish over and over again.

And when you drive on a curved road or change lanes, that shimmy will happen even more often. For instance, when you turn to the left, the outside tire must travel farther than the inside tire, so it spins faster  . This constant changing in spin rate while making turns results in more frequent vibration cancelling and adding action than you would get just cruising down a straight road.

One final note: The cause of each tire-induced vibration does not need to be the same for phase matching to happen. It is entirely possible to have one tire with a poorly seated bead while the other one has a heavy spot.

BALANCING THE WHEELS

1. Before you start, drive the vehicle to heat up the tires. Then, raise the wheels on a lift within 10 minutes  of completing your drive. You must do this to avoid temporary flat spots that could affect the wheel balance.
2. Use the proper centering cone attachment for the wheel that you are balancing. The centering cone must have a low taper  and fit inside the hub bore.
3. Mount the wheel onto the wheel balancer shaft and secure it in place using the proper attachments. If the wheel has a lot of flat surface around its hub bore, a rubber cup attachment works well. But if it has a lot of uneven surfaces (some wheels do because of their elaborate design), you must use a flange plate with studs like the one shown here to ensure accurate center mounting.
4. Make sure the wheel balancer is calibrated. If it needs calibration, go to CALIBRATING THE WHEEL BALANCER .
5. Set the wheel balancer to dynamic balance  .
6. Turn off the measurement rounding feature (you want the measurements to read in 1-gram increments  ).
7. Balance the wheel until its total imbalance reads less than 5 grams  on each side.
8. Set the wheel balancer to static balance  .
9. Turn off the measurement rounding feature (you want the measurements to read in 1-gram increments  ).
10. Measure the imbalance of the wheel, but do not  add any weight. Use chalk for the tire and a permanent marker for the inner rim flange to mark where the weight should go. This is the lightest  spot of the wheel. The light spot should be less than 5 grams  . When you are done, go to MATCHING THE WHEELS TO THE HUBS .

MATCHING THE WHEELS TO THE HUBS

1. Match the light  spot on the wheel to the heavy  spot on the front brake disc and hub assembly. The heavy spot is that ground-off area on the edge of the disc, although not all vehicles have these markings.
2. Turn the brake disc by hand so the heavy spot is facing straight up.
3. Mount the wheel to the hub with the light spot (chalk mark) facing straight up. You want to get the heavy spot on the disc and the light spot on the wheel to line up as closely as possible. The wheel studs may keep you from getting a perfect match, but that is OK. Then, test-drive the vehicle. If the vibration goes away, you are done with this repair. If it is still there, you may need to measure the tire/rim runout with a Hunter GSP9700 wheel balancer and do tire/rim matching.
4. If you cannot find the heavy spot on the disc, mount the wheel and test-drive the vehicle. If you notice there is still too much vibration, remove the wheel, mark one of the studs with a felt-tip pen for reference, then remount the wheel onto the next stud to the right of your reference. Test-drive the vehicle. If the vibration goes away, you are done with this repair; otherwise, repeat this process until you find the ideal mounting location. If the vibration still will not go away, you may need to measure the tire/rim runout with a Hunter GSP9700 wheel balancer and do tire/rim matching.

CALIBRATING THE WHEEL BALANCER

Do this procedure when you are balancing a wheel type or size that you have never balanced before, when you suspect there is a problem with your wheel balancer, or after you have done about 100 wheel balances.

1. Turn off the measurement rounding feature (you want the measurements to read in 1-gram increments)  .
2. Balance a damage-free alloy wheel and tire assembly until both the inner and outer rims read zero  imbalance.
3. Loosen the wing nut attachment, turn the wheel half a turn (180°  ), retighten the wing nut, and recheck the balance.
   • If the imbalance reads 5 grams or less  , the zero calibration is OK. Rebalance the wheel to read zero, then go to step  5 to check the static balance.
   • If the imbalance reads more than 5 grams  , go to step 4.
4. Loosen the wing nut attachment, turn the wheel a quarter turn (90°  ), retighten the wing nut, and recheck the balance.
   • If the imbalance now reads 5 grams or less, the wheel is not centered on the wheel balancer. Make sure you are using the proper centering cone, cup, and wing nut for the wheel you are balancing. If you are not sure, check out the operator's manual or ask the manufacturer what attachments you need. When you have the proper attachments, go back to step  1.
   • If the imbalance still reads more than 5 grams, the wheel balancer needs calibrating, repair, or both. Call the manufacturer for the nearest repair representative.
5. Mount a 5-gram weight to the outer  rim and recheck the balance. The wheel balancer should read 5 ± 2 grams  of imbalance that is 170° to 190°  from that 5-gram weight.
   • If 5 ±  2 grams of imbalance was read, the static balance calibration is OK. Go to step 6 to check the dynamic balance.
   • If 5 ±  2 grams of imbalance was not read, the wheel balancer needs calibrating. Call the manufacturer for the nearest repair representative.
6. At 180°  from the weight you added to the outer rim, mount a 5-gram weight to the inner  rim and recheck the balance. The wheel balancer should read 5 ±  2 grams of imbalance 170° to 190°  from both of the weights you mounted.
   • If 5 ±  2 grams of imbalance was read, the dynamic balance calibration is OK and the wheel balancer is ready to use.
   • If 5 ±  2 grams of imbalance was not  read, the wheel balancer needs calibrating. Call the manufacturer for the nearest repair representative.

   Most steering wheel shimmy or chassis vibration problems can be fixed by balancing the wheels and matching them to the hubs. But if that does not work, you may need to measure the tire/rim runout. Excessive runout under load can cause vibration that wheel balancing will simply not fix.

READING TIRE/RIM RUNOUT WITH A HUNTER GSP9700 WHEEL BALANCER

To reduce the effect of runout, you must find the radial force variation (RFV)  of each tire and rim, then match the tires to the rims by indexing their peak RFV areas. Matching tires to rims this way helps cut down on wheel vibration.

To accurately read tire/rim runout, you need equipment that can simulate road force on a wheel and show you the peak RFV area on the tire and on the rim. The Hunter GSP9700 wheel balancer, besides being a wheel balancer, can accurately calculate peak RFV readings on tires and rims. If your shop does not have a GSP9700, visit Hunter's GSP9700 website at www.GSP9700.com  or find another shop in your area that does.

1. To ensure you are getting the right tire/rim runout readings, raise the vehicle so all four wheels are off the ground within 10 minutes  of completing your test-drive. You must do this to avoid temporary flat spots that could affect the wheel balance.
2. Make sure all four tire pressures read exactly  as listed on the driver's doorjamb label.
3. Mark each tire's position (L/F, R/F, L/R, and R/R).
4. Remove all wheel weights and clean off any mud from the rims. Wheel weights will keep you from reading RFM and any extra weight will cause wheel imbalance.
5. Clean out any pebbles, mud, or other debris trapped between the tire treads. Anything causing a bump on the tires will throw off RFM and balancer readings.
6. Inspect the wheels for damage. Tire or rim damage can cause high RFM readings and wheel imbalance.
7. Make sure the arbor and baseplate threads on the wheel balancer are clean.
8. Make sure all mating surfaces between the wheel and the wheel balancer are clean, then mount the wheel.
   NOTE: Use the GSP9700 centering check feature (it is on software version 2.1 or higher) to check for a possible centering error between the rim and the wheel balancer.
9. Use the wheel balancer to find the initial RFM readings (pounds and peak locations) of the tire, the rim, and the tire/rim combination. For more information, see the operator's manual. If the RFM is higher than 10 pounds,  do the match mounting procedure in the manual. If the RFM is still higher than 10 pounds after doing that, replace the tire.
10. After you have found the problem wheel, remount the tire.
    • Fully deflate the tire and break the bead seal from the rim.
    • Clean off any dirt, tar, or rocks from the rim and inspect the tire bead area for any debris that could keep the bead from properly sealing on the rim.
    • Use tire mounting paste to coat all of the areas where the tire touches the rim (inner and outer tire beads, rim flange, middle of the rim). Never  use soap and water or a silicone spray. If your shop does not have tire mounting paste, there are a number of brands commercially available. If the vehicle has direct TPMS, be careful not to get any of that paste on the tire pressure sensor.
    • Seal the tire beads on the rim by fully inflating the tire to the max pressure shown on the sidewall.
    • Fully deflate the tire, then inflate it to the recommended cold inflation pressure listed on the driver's doorjamb label.
11. Mount the wheel on the vehicle and go for a test-drive. If the vibration is gone, you are done with this repair. If it is still there, then look for other possible causes.