San Diego Engine Balancing
215 Denny Way #C
El Cajon, Ca 92020
Vibration
Diagnosis
Know the history of the condition. Did it
start all of a sudden? Was it related to some occurrence like an accident or previous part replacement? Know how the condition
made itself known, it may be an important clue to the cause.
Terms
Boom: A cycling, rhythmic noise
often accompanied by a sensation of pressure on the ear drums.
Bound
Up:Refers to a stressed, rubber-mounted component that transmits any NVH which would normally be absorbed
by the mount (see neutralize).
Cps: Cycle Per Seconds. (HZ)
Controlled Rear Suspension Height:The height at
which the components of a particular vehicle should be set when drive-line angle measurements are made.
Drive-Line Angles:Difference of alignment between the transmission
output shaft, drive-shaft, and rear axle pinion centerline.
Engine Run Up Test: Operation
of engine through normal RPM range while vehicle is sitting still. Used for engine vibration check.
Extension Housing Damper:A
counterweight attached to the rear of the transmission extension housing and designed to "soak up" or damp unwanted
drive-line or power-train vibrations.
Engine
Imbalance: Some component in the engine which is normally smoothly balanced now causing a perceptible
vibration in the vehicle.
Imbalance
also Unbalance:Out of balance; more weight in one side of a rotating component causing shake or vibration.
NVH, Noise, Vibration, Harshness.
Neutralize
or Normalize: To return to unstressed position. Used to describe mounts.
Shake: Low frequency vibration, usually results
in visual movement of components.
Tire
Force Vibration: Tire vibration caused by vibration in the construction of the tire resulting in a vibration
when the tire rotates against the pavement. This condition may be present on perfectly round tires because of vibrations in
the inner construction. May occur at wheel rotation frequency or twice rotation frequency.
Vibration:Cyclic movement of a component that results
in a sound or feel of movement.
Identifying the Condition
High Speed
Shake:(50 mph and up) This condition produces a VISIBLE shake and pumping feel in the steering column,
seats or floor pan. It is a low frequency vibration (9-15 cps). It may be or may not be increased by applying brakes lightly.
TIP-in-MOAN (15-50 mph) when accelerating between 15-50 mph, this vibration produces a "moan" or high frequency
feel in the floor pan. It is usually worse at particular engine speed and at a particular throttle setting during acceleration
at that speed. It may also produce a moaning sound depending on what component is causing it.
Drive-Line Vibration:(50 mph
and up) This is not a visible vibration, but can be felt in the floor pan as a rumble, buzz, hum, drone or boom. It is independent
of engine speed, and will occur at the same speed in any gear. It will exist in all drive modules, but may vary somewhat in
acceleration, deceleration, float, or coast modes. In some cases the drive-line vibration is eliminated in the float mode.
Incorrect Drive-Line Angle:(25-40
mph) This vibration, a shuddering feel or audible rumble, occurs during the acceleration and/or deceleration with the degree
of vibration depending on the amount of torque applied to the drive-shaft. It is very intense during heavy acceleration or
deceleration and very light during cruise or neutral coast. The vibration is hard to duplicate with vehicle support on
a hoist, since wheels are coasting free.
Engine
or Accessory Vibration: (all speeds) This vibration occurs at any vehicle speed, but always at the same
engine rpm. It will disappear in neutral coast. The vibration can be duplicated by operating the engine at the problem rpm
while the vehicle is sitting still. It can be caused by any component from the fan back to the clutch or torque converter
and by anything that turns at engine speed when the vehicle is stopped.
High Speed Shake Diagnosis
1. Accelerate to the speed which the shake occurred
and note.
2. Inspect
tires: Raise vehicle on hoist. Inspect tires for extreme wear or damage, cupped or flat spots. Check suspension
components for misalignment abnormal wear, or damage that may contributed to the tire wear. Correct suspension problems, replace
damaged tires, and road test.
3. Inspect wheel bearings: Spin tires by hand to check for wheel bearing roughness. Check
bearing end play. Adjust or replace.
4.
Wheel/Tire-Run-Out:Spin front wheels at low speed with a wheel balance
spinner, observing wheel/tire run-out. Balance wheels.
5.
Drive Train: Engage drive train and carefully accelerate the drive wheels.
6. Drive Wheels:
Remove rear wheels. Secure brake drums, if so equipped, by installing the lug nuts reversed. Carefully accelerate the drive
wheels. Balance rear wheels.
7. Rear Drum of Rotors: Remove the brake drums or rotors. Carefully accelerate the drive
wheels. Replace the drums or rotors.
8. Axle Run-Out: With drum or rotor removed, check axle flange face run-out,
lug bolt circle radial run-out, drum/rotor pilot radial run-out. Replace axle shaft or hub.
9. Wheel Run-Out:
Install wheels and tires in original positions. Check all wheels for total radial and lateral tire run-out (0.070 in). Check
wheel rim run-out, radial and lateral. If either exceeds (0.045 in) replace.
10. Tire Run-Out: Check total lateral
and radial run-out (0.070 in).
11. Wheel Balance: Balance all wheels not previously balanced tested.
12. Substitute Wheels and Tires:
Substitute a known good set or wheels and tires.
Tip-In Moan Diagnosis
1. Air Cleaner: Check air
cleaner for proper installation of base gasket, lid element, and air inlet duct assembly.
2. Power-Train resonance: Loosen all
converter or clutch housing-to-engine attaching bolts 3/4 turn and road test. Re-tighten bolts. Check for presence of transmission
extension damper and that it is installed as required.
3.
Engine Mounts:Normalize engine mounts by loosening them, and with engine running, shifting
transmission from neutral to drive and back to neutral. With manual transmission, load engine by slipping clutch in gear.
Re-tighten and road test.
4. Exhaust
System:Warm up system to normal operating temperature. Loosen all hanger attachments and reposition hanger
until they hang free and straight. Then loosen all flange joints, and with engine running shift transmission from neutral
to drive and back to neutral (or load engine with clutch), and re-tighten all hangers clamps and flanges. Road Test.
Drive-Line Vibration Diagnosis
1. Wheels and Tires:
Verify that the observed condition is not a high speed shake caused by wheels/tires.
2. Drive-shaft: Inspect drive-shaft for physical damage undercoating,
or improperly seated, worn or binding universal joints. Check index marks (paint spots) on rear of shaft and pinion yoke or
companion flange. If these marks are more than 90 degrees apart, re-index and align marks.
3. Drive-Shaft Run-Out: With vehicle on hoist measure
run-out at front, center, and ear of drive-shaft (0.035 in).
4.
Drive-Shaft Vibration: The drive-shaft can be re-index to any eight positions to minimize imbalance.
Balance drive-shaft if vibration still exists. After balancing install an axle pinion damper.
Engine Accessory Vibration Diagnosis
1. Engine Run-Up:
Run-up to problem rpm with vehicle stationary. If vibration occurs see below.
2. Drive Belts and Pulleys: With engine stopped, inspect all
engine accessory drive belts and pulleys for wear or damage. Check belt tension.
3. Mounting Hardware: Inspect mounting brackets and adjusting
hardware for proper alignment and tightness. Run-up to problem rpm and with a stethoscope type device, check each component.
If the source cannot be detected, remove each belt at a time.
