Manual Transmission/Transaxle: Technical Service Bulletins
Manual Transmission - M/T Operating Characteristics
Bulletin No.: 03-07-29-004G
Date: December 15, 2010
Subject: Manual Transmission Operating Characteristics
2011 and Prior GM Passenger Cars and Light Duty Trucks (Including Saturn)
2009 and Prior Chevrolet and GMC Medium Duty Trucks
2006-2010 HUMMER H3
with Manual Transmission
This bulletin is being revised to add the 2011 model year and to add Cold Operation information. Please discard Corporate Bulletin Number
03-07-29-004F (Section 07 - Transmission/Transaxle).
Even though this bulletin attempts to cover operating characteristics of manual transmissions, it cannot be all inclusive. Be sure to compare any
questionable concerns to a similar vehicle and if possible, with similar mileage. Even though many of the conditions are described as
characteristics and may not be durability issues, GM may attempt to improve specific issues for customer satisfaction.
The purpose of this bulletin is to assist in identifying characteristics of manual transmissions that repair attempts will not change. The following are
explanations and examples of conditions that will generally occur in all manual transmissions. All noises will vary between transmissions due to build
variation, type of transmission (usually the more heavy duty, the more noise), type of flywheel and clutch, level of insulation, etc.
Many transmission noises are created by the firing pulses of the engine. Each firing pulse creates a sudden change in angular acceleration at the
crankshaft. These changes in speed can be reduced with clutch damper springs and dual mass flywheels. However, some speed variation will make it
through to the transmission. This can create noise as the various gears will accel and decel against each other because of required clearances.
Manual transmission operation will be affected by temperature because the transmission fluid will be thicker when cold. The thicker fluid will increase
the amount of force needed to shift the transmission when cold. The likelihood of gear clash will also increase due to the greater time needed for the
synchronizer assembly to perform its function. Therefore when the transmission is cold, or before it has reached operating temperature, quick, hard shifts
should be avoided to prevent damage to the transmission.
Rattling or grinding (not to be confused with a missed shift type of grinding, also described as a combustion knock type of noise) type noises usually
occur while operating the engine at low RPMs (lugging the engine). This can occur while accelerating from a stop (for example, a Corvette) or while
operating at low RPMs while under a load (for example, Kodiak in a lower gear and at low engine speed). Vehicles equipped with a dual-mass flywheel
(for example, a 3500 HD Sierra with the 6-speed manual and Duramax(R)) will have reduced noise levels as compared to vehicles without (for example,
a 4500 Kodiak with the 6-speed manual and Duramax(R)). However, dual-mass flywheels do not eliminate all noise.
There are often concerns of rattle while idling in neutral with the clutch engaged. This is related to the changes in angular acceleration described earlier.
This is a light rattle, and once again, vehicles with dual mass flywheels will have reduced noise. If the engine is shut off while idling in neutral with the
clutch engaged, the sudden stop of the engine will create a rapid change in angular acceleration that even dual mass flywheels cannot compensate.
Because of the mass of all the components, this will create a noise. This type of noise should not be heard if the clutch is released (pedal pushed to the
Backlash noise is created when changing engine or driveline loading. This can occur when accelerating from a stop, coming to a stop, or applying and
releasing the throttle (loading and unloading the driveline). This will vary based on vehicle type, build variations, driver input, vehicle loading, etc. and
is created from the necessary clearance between all of the mating gears in the transmission, axle(s) and transfer case (if equipped).