M/T - Operational Characteristics
Information IB07-05-S006Issue Date: NOVEMBER 2007
Affected Vehicles:
2007-2008 Isuzu i-290 (TI) with Manual Transmission
2006 Isuzu i-280 (TI) with Manual Transmission
Service Information
This bulletin is being revised to add the 2008 model year.
IMPORTANT:
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 possible, with similar mileage.
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 manual transmissions. 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.
Basic Information
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.
Gear Rattle
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 or while operating at low RPMs while under a load.
Neutral Rattle
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. 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. 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 floor).
Backlash
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).
Shift Effort
Shift effort will vary among different style transmissions and synchronizer designs. Usually the more heavy duty the transmission the higher the shift effort is because of the increased mass of the components. Shift effort can also be higher in cold weather because the fluid will be thicker. To reduce shift effort do not attempt to rush the shift allow the synchronizers to work as designed. Shifting harder will only increase the chance of rushing past the synchronizer leading to grinding while shifting.
Non-Synchronized Gears
Some transmissions in 1st gear and reverse gears in various transmissions may be nonsynchronized. This means there is not a mechanism to match input and output shaft speeds to allow for a smooth shift. This function is left up to the driver. This can be noticed if a shift into 1st or reverse is attempted while the vehicle is rolling or before the input shaft stops rotating leading to a gear grind. The grinding can be reduced by coming to a complete stop and pausing for a moment before shifting into the 1st or reverse gear. Some slight grinding can be expected.
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