Know the Real Causes of Vibration related comebacks, GM Bulletin does not fully explain the importance.
Condition 1: 1st Order Tire Suggestions (Freq 11-14 hz at 60 mph or 97 km/h)
Measurements
Remove the tire and wheel assemblies from the vehicle and perform the Road Force Variation (RFV) measurement.
Important: Prior to taking any measurements, the assemblies MUST all pass a center check.
Note: Rule of Thumb for vibrations.
Use a Low Taper Collet that fits correctly in back side of wheel and back cone assembly. Use a finger plate that uses lug holes in wheel to mount wheel to balancer. This mounting process will help ensure wheel is properly mounted before balancing assembly. (Mounting errors are the cause of 60% vibration related comebacks.
Steering Wheel = Front Wheels
Floor/Seat Track/Body = Rear Wheels
Document the before and after Road Force Variation (RFV) numbers.
Road Force Specifications
P-Metric tires on passenger cars
15 lbs (6.8 kg) or less
P-Metric tires on light trucks
15 lbs (6.8 kg) or less
LT – tires on light trucks
15 lbs (6.8 kg) or less
Note: These numbers are lower than what is currently published in service information as some vehicles react to parts that are near the high limit. These numbers SHOULD NOT be used if you do not have a tire speed related disturbance.
Repair:
For any assembly that has an out of balance condition (greater than 0.25 oz), remove the weights and correct the condition utilizing normal balancing techniques.
For any assembly having RFV measurements beyond the specification above, vectoring the tire on the rim should be utilized prior to tirereplacement. If this does not bring the assembly within specification, the tire should be replaced.
If assembly is calling for more than 3oz Static while balancing, deflate tire and spin tire 180 degrees on wheel and reinflate. Re-Check Static reading and if under 3oz proceed to ProBalance.
Additional Notes on Balancing:
Use a COATS Direct Drive Balancer with ProBalance Technology for smoothest ride. ProBalance ensures ALL Residual unbalance vibrations are reduced to under .10oz Static (Hop or up and down vibration) and Dynamic (Shimmy or wobble side to side vibration).
Always perform a centering check.
A Hunter Balancer/Road Force Balancer should not be set to “Smart Weight.”
All tires need to be balanced under 0.25 oz (both static and dynamic).
When using the Hunter – Balancer/Road Force Balancer, removal and remounting to the tire balancer should be performed to re-check balance and verify that results are repeatable to 0.25 oz or less.
Check Wheel Runout.
Important: When replacing tires, the road force should be checked before a test drive and after a test drive (min of 10-15 miles or 16-24 km/h). Road force on new tires will change dramatically after being warmed up (as much as a 20 lb reduction). After the test drive, the tire’s road force should be checked. If acceptable RFV cannot be achieved, first try vectoring the tire on the rim before an alternate tire is utilized. Also refer to the Information in the latest version of Corporate Bulletin Number 13-03-10-002: Diagnostic Tips for Difficult to Resolve Tire/Wheel Vibration Concerns. Some more information is needed on how to check the assemblies for 2nd, 3rd, and 4th order RFV.