Chevrolet Silverado / GMC Sierra. Service manual — part 838

FLUID LEAKS FROM FLUID FILL TUBE AND/OR VENT

FLUID LEAKS FROM TRANSMISSION INPUT

Low and Reverse clutch slipping, leaks at
piston seals, Low and Reverse clutch plates
worn

Inspect the Low and Reverse clutch plates and
piston seals. Replace/rebuild as necessary.

Condition

Action

Dipstick loose

Tighten the cap. Replace the cap if necessary.

Fluid level too high

Drain the fluid to the proper level. Refer to
Transmission Fluid Check.

Fluid level too low

Add fluid to the proper level. Refer to
Transmission Fluid Check.

Breather stopped up - clogged

Clean or replace the breather.

Dipstick or fill tube seal worn

Replace the seals or dipstick.

Incorrect dipstick marking

Calibrate the dipstick.

Fluid contaminated with engine coolant or
water

Drain and replace fluid. Locate and fix source
of additional fluid. Refer to Transmission
Fluid Check andAutomatic Transmission
Fluid and Filter Replacement.

Condition

Action

Torque converter seal leaks

Replace the torque converter seal. Refer to
Torque Converter Fluid Seal Replacement.

Front support bolt seals leaking

Replace the bolt seals. Refer to Torque
Converter Housing Bolt Seal Replacement.

Converter leaks

Inspect the converter seals, cracked converter
pump tangs, converter cover, or converter
housing porosity. Replace the parts as
required.

Spin-on filter leaking

Replace the filter. Refer to Automatic
Transmission Fluid and Filter
Replacement.

Main pressure plug leak

Replace or torque the main pressure plug.
Refer to Automatic Transmission Fluid
Pressure Test Hole Plug Replacement.

2008 Chevrolet Silverado 1500

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

Silverado

FLUID LEAKS FROM TRANSMISSION OUTPUT

INTERMITTENT BUZZING NOISE

Pump bushing shows excessive wear

Rebuild and repair the pump.

Condition

Action

Faulty or missing seal at output flange/yoke Install a new seal assembly in the transmission

rear cover. Refer to Rear Propshaft Shaft
Seal Replacement.

Machine lead on output flange/yoke seal
surface

Replace the flange/yoke. Refer to Output
Flange/Yoke Replacement.

Rear cover porosity

Repair or replace the cover.

Flange/yoke worn at seal surface

Replace the flange/yoke. Refer to Output
Flange/Yoke Replacement.

Insufficient sealant around seal OD

Install a new seal assembly in the transmission
rear cover. Refer to Rear Propshaft Shaft
Seal Replacement.

Damaged or missing output bolt washer seal Replace the output bolt sealing washer. Refer

to Output Flange/Yoke Replacement.

Damaged, missing, or loose output flange
bolt

Replace and/or torque the output flange bolt.
Refer to Output Flange/Yoke Replacement.

Condition

Action

Low fluid level

Add fluid to the proper level. Refer to
Transmission Fluid Check.

Air leak in oil suction filter canister

Replace the oil suction filter. Refer to Oil Pan
Replacement.

Clogged suction filter

Replace the filter. Refer to Oil Pan
Replacement.

Aerated fluid causes noisy pump

Correct the fluid level. Refer to Transmission
Fluid Check.

Low main pressure causes main regulator
valve to oscillate

Refer to Low Main Line Pressure in All
Ranges and Low Main Line Pressure in
Specific Ranges, Normal Pressure in Other
Ranges.

2008 Chevrolet Silverado 1500

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

Silverado

LOW MAIN LINE PRESSURE IN ALL RANGES

LOW MAIN LINE PRESSURE IN SPECIFIC RANGES, NORMAL PRESSURE
IN OTHER RANGES

LOW LUBRICATION PRESSURE

Condition

Action

Incorrect fluid level

Correct the fluid level. Refer to
Transmission Fluid Check.

Plugged or faulty suction filter

Clean or replace the oil suction filter element.
Refer to Oil Pan Replacement.

Main pressure regulator valve sticking

Overhaul the control module assembly.

Leaking solenoids in control valve body
assembly

Replace the solenoids. Refer to Control
Valve Solenoid Replacement (SS1, SS2,
SS3, TCC, and MAIN MOD) or Control
Valve Solenoid Replacement (PCS1 and
PCS2).

Main pressure regulator valve spring weak,
broken, or missing

Inspect the spring and replace, if necessary.

Control module body leakage - separator
plate not flat, loose control valve body bolts

Replace or rebuild the control module
assembly. Care should be taken when
removing and labeling shift springs.

Faulty or incorrect fluid pressure gage

Repair or replace the gage.

Oil pump worn or damaged

Replace or rebuild the oil pump.

Leak in suction circuit

Inspect the suction circuit for leaking seal,
gasket, or mating surface.

Condition

Action

Seal leak

Replace the seals that are causing low
pressure in a particular range.

Condition

Action

Incorrect fluid level

Correct the fluid level. Refer to
Transmission Fluid Check.

Plugged suction filter

Clean or replace the oil suction filter. Refer to
Oil Pan Replacement.

2008 Chevrolet Silverado 1500

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

Silverado

CONTAMINATED TRANSMISSION FLUID

EXCESSIVE FLARE - ENGINE OVERSPEED ON WIDE-OPEN THROTTLE

Plugged control main filter

Replace the filter.

Excessive internal fluid leakage

Inspect other pressures. Refer to Low
Main Line Pressure in All Ranges and
Low Main Line Pressure in Specific
Ranges, Normal Pressure in Other
Ranges.

Inspect the control module mounting
bolts.

Inspect the lubrication valve and spring.

Inspect the converter housing to
separator plate gasket.

Cooler lines restricted or leaking

Inspect for kinks and leakage. Reroute or
replace lines as necessary.

Lubrication regulator valve sticking

Clean or replace the regulator valve.

Converter relief valve sticking

Clean or replace the converter relief valve.

Cooler plugged

Clean or replace the cooler.

Faulty gage

Repair or replace the gage.

Condition

Action

Failure to change fluid and filters

Change the fluid and install new filters. Refer
to Automatic Transmission Fluid and
Filter Replacement.

Excessive heat

Inspect the cooling system for restrictions and
proper capacity.

Substandard fluid

Use recommended fluid. Refer to
Transmission General Specifications .

Clutch/transmission failure

Overhaul the transmission.

Condition

Action

Incorrect fluid level

Add fluid to the proper level. Refer to
Transmission Fluid Check.

Sticking valves in control valve body
assembly

Rebuild the control valve body assembly.
Refer to Control Valve Body Replacement.

2008 Chevrolet Silverado 1500

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

Silverado