Chevrolet Silverado / GMC Sierra. Service manual — part 739

IF SHUDDER OCCURS AFTER TCC HAS APPLIED

If shudder occurs after the TCC has applied, most of the time there is nothing wrong with the
transmission.

The TCC is not likely to slip after the TCC has been applied. Engine problems may go unnoticed
under light throttle and load, but they become noticeable after the TCC apply when going up a
hill or accelerating. This is due to the mechanical coupling between the engine and the
transmission.

Once TCC is applied, there is no torque converter (fluid coupling) assistance. Engine or driveline
vibrations could be unnoticeable before TCC engagement.

Inspect the following components in order to avoid misdiagnosis of TCC shudder. An inspection
will also avoid the unnecessary disassembly of a transmission or the unnecessary replacement of a
torque converter.

Spark plugs-Inspect for cracks, high resistance or a broken insulator.

Plug wires-Look in each end. If there is red dust (ozone) or a black substance (carbon)
present, then the wires are bad. Also look for a white discoloration of the wire. This
indicates arcing during hard acceleration.

Coil-Look for a black discoloration on the bottom of the coil. This indicates arcing while
the engine is misfiring.

Fuel injector-The filter may be plugged.

Vacuum leak-The engine will not get a correct amount of fuel. The mixture may run rich or
lean depending on where the leak occurs.

EGR valve-The valve may let in too much or too little unburnable exhaust gas and could
cause the engine to run rich or lean.

MAP/MAF sensor-Like a vacuum leak, the engine will not get the correct amount of fuel for
proper engine operation.

Carbon on the intake valves-Carbon restricts the proper flow of air/fuel mixture into the
cylinders.

Flat cam-Valves do not open enough to let the proper fuel/air mixture into the cylinders.

Oxygen sensor-This sensor may command the engine too rich or too lean for too long.

Fuel pressure-This may be too low.

Engine mounts-Vibration of the mounts can be multiplied by TCC engagement.

Axle joints-Check for vibration.

TP Sensor-The TCC apply and release depends on the TP Sensor in many engines. If the TP

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Sensor is out of specification, TCC may remain applied during initial engine loading.

Cylinder balance-Bad piston rings or poorly sealing valves can cause low power in a
cylinder.

Fuel contamination-This causes poor engine performance.

Replace the torque converter if any of the following conditions exist:

External leaks appear in the hub weld area.

The converter hub is scored or damaged.

The converter pilot is broken, damaged, or fits poorly into the crankshaft.

You discover steel particles after flushing the cooler and the cooler lines.

The pump is damaged, or you discover steel particles in the converter.

The vehicle has TCC shudder and/or no TCC apply. Replace the torque converter only after
all hydraulic and electrical diagnoses have been made. The converter clutch material may be
glazed.

The converter has an imbalance which cannot be corrected. Refer to Flexplate/Torque
Converter Vibration Test.

The converter is contaminated with engine coolant which contains antifreeze or water.

An internal failure occurs in the stator roller clutch.

You notice excessive end play.

Overheating produces heavy debris in the clutch or converter ballooning.

You discover steel particles or clutch lining material in the fluid filter or on the magnet,
when no internal parts in the unit are worn or damaged. This condition indicates that lining
material came from the converter.

Do not replace the torque converter if you discover any of the following symptoms:

The oil has an odor or the oil is discolored, even though metal or clutch facing particles are
not present.

The threads in one or more of the converter bolt holds are damaged. Correct the condition
with a new thread inset.

Transmission failure did not display evidence of damaged or worn internal parts, steel
particles or clutch plate lining material in the unit and inside the fluid filter.

The vehicle has been exposed to high mileage only. An exception may exist where the lining
of the torque converter clutch dampener plate has seen excess wear by vehicles operated in
heavy and/or constant traffic, such as taxi, delivery, or police use.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

FLEXPLATE/TORQUE CONVERTER VIBRATION TEST

ISOLATING VIBRATION

To isolate and correct a flywheel or torque converter vibration, separate the torque converter
from the flywheel to determine if vibration is in the engine or transmission.

1. With the engine at idle speed and the transmission in PARK or NEUTRAL, observe the

vibration.

2. Turn the engine OFF.

3. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle .

4. Remove the transmission converter cover bolts and the cover.

5. Mark the relationship of the converter to the flywheel.

6. Remove the bolts attaching the converter to the flywheel.

7. Slide the torque converter away from the flywheel.

8. Rotate the flywheel and torque converter to inspect for defects or missing balance weights.

9. Lower the vehicle.

10. With the engine at idle speed and the transmission in PARK or NEUTRAL, observe the

vibration. Refer to Diagnostic Starting Point - Vibration Diagnosis and Correction .

11. Turn the engine OFF.

INDEXING TORQUE CONVERTER

To determine and correct a torque converter vibration, the following procedure may have to be
performed several times to achieve the best possible torque converter to flywheel balance.

1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle .

2. Rotate the torque converter one bolt position.

NOTE:

Some engine/transaxle combinations cannot be balanced in this
manner due to restricted access or limited clearances between the
torque converter bolts and the engine. Ensure that the bolts do not
bottom out in the lug nuts or the torque converter cover which
could dent and cause internal damage.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 7: View Of Torque Converter Hub In Engine Crankshaft
Courtesy of GENERAL MOTORS CORP.

3. Align the torque converter hub (2) in the engine crankshaft (3) and install the torque

converter to flywheel bolts.

4. Lower the vehicle.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado