Chevrolet Silverado / GMC Sierra. Service manual — part 833

You may notice a torque converter whine when the vehicle is stopped and the transmission is in
DRIVE or REVERSE. This noise will increase as you increase the engine RPM. The noise will
stop when the vehicle is moving or when you apply the torque converter clutch, because both
halves of the converter are turning at the same speed.

Perform a stall test to make sure the noise is actually coming from the converter.

1. Bring the vehicle to a complete stop using the service brake.

2. Ensure that the engine is at low idle RPM.

3. Put the transmission in P, PARK.

4. Engage the P, PARK, range by slowly releasing the service brake.

5. Apply the emergency brake and/or parking brake, if present, and ensure it is properly

engaged.

6. If the vehicle will be unoccupied with the engine running, chock the wheels and take any

other steps necessary to keep the vehicle from moving.

7. Place your foot on the brake.

8. Place the range selector in DRIVE.

9. Depress the accelerator to approximately 1,200 RPM for no greater than 6 seconds. Listen

for torque converter noise. A torque converter noise will increase under this load.

TORQUE CONVERTER CLUTCH SHUDDER

The key to diagnosing TCC shudder is to note when it happens and under what conditions.

TCC shudder which is caused by the transmission, should only occur during the apply or release
of the converter clutch. Shudder should never occur after the TCC piston is fully applied.

If the shudder occurs while the TCC is applying, the condition could be within the transmission or
the torque converter. Something is causing one of the following conditions to occur:

Something is not allowing the clutch to become fully engaged.

Something is not allowing the clutch to release.

usually noticeable in PARK, NEUTRAL and all other gear ranges.
Pump whine will vary with line pressure.

NOTE:

You may damage the transmission if you depress the
accelerator for more than 6 seconds.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

The clutch is releasing and applying at the same time.

One of the following may be causing the conditions to occur:

Leaking turbine shaft seal rings

A restricted release orifice

Defective friction material on the TCC piston

IF SHUDDER OCCURS AFTER THE TCC HAS APPLIED

As mentioned above, the TCC is not likely to slip after the TCC has been applied. Engine
conditions 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 the 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
also avoids 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 ozone dust or a black carbon substance present, the wires
are bad. Also, inspect for a white discoloration of the wire. This indicates arcing during
hard acceleration.

Coil

Inspect for black discoloration on the bottom of the coil. This indicates arcing while the
engine is misfiring.

Fuel injector

IMPORTANT: If shudder occurs after the TCC has applied, most likely there is

nothing wrong with the transmission.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

The filter may be plugged.

Vacuum leak

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

Exhaust gas recirculation (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.

Manifold absolute pressure (MAP) or mass air flow (MAF) sensor - possibly a vacuum leak

The engine will not receive 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 far enough to let the proper fuel/air mixture into the cylinders.

Oxygen sensor

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

Fuel pressure

Fuel pressure may be too low.

Engine mounts

Vibration of the mounts can be multiplied by TCC engagement.

Axle joints

Inspect for vibration.

Throttle position (TP) sensor

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

The TCC apply and release depends on the TP sensor in many engines. If the TP sensor is
out of specification, the TCC may remain applied during initial engine loading.

Cylinder balance

Malfunctioning piston rings or poorly sealed valves can cause low power in a cylinder.

Fuel contamination

Fuel contamination causes poor engine performance.

TORQUE CONVERTER EVALUATION AND DIAGNOSIS

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

An internal failure occurs in the stator race

Overheating produces heavy debris in the clutch

You discover steel particles or clutch lining material in the control main filter or suction
filter, or on the magnets, 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

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado