24-NA-262 Service Bulletin/Repair Instructions

Bulletin No.: 24-NA-262
Service Bulletin
Date: November, 2024
INFORMATION

Subject:
Diagnostic Tip for 10L1000 Transmission Noise
Brand:
Model:
Chevrolet
Silverado 2500HD/

3500HD
GMC
Sierra 2500HD/

3500HD
Model Year:

from
to
2020
2025
VIN:

from
Engine:
Transmission

:
L5P, L8T
MGM, MGU,

MKM
to
Involved Region or Country
United States, Canada, Middle East, Israel, Palestine, Australia/New Zealand
Condition
Some customers may comment on whine noises from the automatic transmission.
Information
To aid in transmission diagnosing, refer to the noise examples below.
Important: Service agents must comply with all International, Federal, State, Provincial, and/or Local laws

applicable to the activities it performs under this bulletin, including but not limited to handling, deploying,

preparing, classifying, packaging, marking, labeling, and shipping dangerous goods. In the event of a

conflict between the procedures set forth in this bulletin and the laws that apply to your dealership, you

must follow those applicable laws.
Potential Noises Found in Park

Park-Transmission Oil Pump Aeration/Cavitation

Aeration is the introduction of air into the transmission fluid (pump inlet).

Erratic whining sound due to uneven distribution of air.

Cavitation occurs when cavities are formed due to a drop in fluid pressure (outlet).

Rattling, whirling/roaring or grinding sounds are all possible.

• 75°C (167°F) Pump Aeration Cavitation 900 RPM Steady State

• 75°C (167°F) Pump Aeration Cavitation 650-1500 RPM Sweep
Common Causes:

• Low fluid level

• Plugged/mis installed filter
Copyright 2024 General Motors. All Rights Reserved.
Page 2
November, 2024
Bulletin No.: 24-NA-262
6769556
• Torn/damaged filter O-ring

• Transmission running max line pressure due to DTCs

Park Transmission Oil Pump Gear Mesh Whine

Unlike previous generation HD transmissions (6 speed), the 10 speed Allison model transmission utilizes a (3) spur

gear design (driven off of the torque converter) to drive the transmission oil pump.

Due to the 3–spur gear design, some transmissions may exhibit a whine noise while in park or driving and may get

louder as engine speed or transmission temperature increases.

Isolating the whine to the oil pump gears can often be done by replicating the complaint in park and sweeping engine

speed slowly from base idle to 2500 RPM.

If whine can be reproduced in park, replacement of the transmission front support and/or transmission oil pump often

corrects the whine complaint.

Start Up/Garage Shift Clunk

Described as an infrequent audible thud that delayed 400–700ms after either a key start or garage shift event.

Severity of thud depends on the load that's placed on the driveline.

Previous root cause work determined noise is related to the C2 clutch application at high line pressure causing the

rotating components in park to stop too quickly.

C2 clutch calibration has been modified to assure the C2 knockdown area is pressurized in park and neutral when

C2 is being applied.
Bulletin No.: 24-NA-262
November, 2024
Page 3
6769524
• Key Start

• Garage Shift
Common Complaints in Drive

Reaction Gearset Whine (Gearset One)

With variation in gear tooth finish and positional control, some customers may experience whine from the reaction

planetary gearset during light to moderate driving conditions.

Most common conditions to hear whine from the reaction gearset is in 4th and 5th gear (20-35 MPH) (32-56 KPH).

Reaction gearset is active in gears 3-6 and 8-10 so depending on severity it may be possible to hear in gears other

than 4/5.

Frequency of whine will change as transmission shifts gears due to component rotation speeds being changed.

Utilizing manual tap to shift through gears is a good way to verify what gears whine in present in.

Note: Whine from the reaction gearset should not be present in 7th gear due to the 1:1 ratio and gears being locked.

If whine is present in 7th gear, issue likely lives with some other component.
Page 4
November, 2024
Bulletin No.: 24-NA-262
Underbody Gear Rattle (7th Gear Only)
6769588
While rare, rattle during light acceleration (10–15% throttle) in 7th gear only may be observed.

Size of the idler gear inner diameter can affect the interference fit of the pressed in bearing reducing the overall

axial/radial clearance of the bearing balls.

The gear free lock will increase or decrease depending on that interference fit:

-
High interference fit can create gear rattle
-
Low interference fit does not produce rattle
Increasing line pressure can reduce rattle by overcoming the drag torque.

Note: The feature to change line pressure using Techline Connect is not active, otherwise that would be a means to

verify.
Version
1
Modified
Released November 25, 2024
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these

technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper

service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job

properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your

vehicle will have that condition. See your GM dealer for information on whether your vehicle may beneﬁt from the

information.
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