Automatic Transmission/Transaxle: Description and Operation
AUTOMATIC TRANSMISSION COMPONENTSThe automatic transmissions used in Jeep vehicles are fully automatic, three speed, hydraulically operated units with a compound planetary gear system. A three element torque converter is used for all applications. A manually operated floor gearshift linkage is used to select the desired gear range. Transmission shift points are controlled by an externally mounted throttle linkage. The transmission case and converter housing consist of a one-piece aluminum casting. An aluminum adapter housing is used to connect the transmission to the various transfer case models.
CLUTCH-BAND-GEAR SYSTEM
Transmission Model 904 H.D. has two multiple disc clutches, two bands and actuating servos, an overrunning clutch and two planetary gear sets, all of which combine to provide one reverse and three forward gear ranges. The planetary gear sets are connected by a common sun gear. The sun gear is interconnected to the multiple disc clutches through the driving shell which is splined to the sun gear and front clutch retainer.
The Model 904 H.D. transmission has a wide ratio planetary gear set. Ratios are:
^ lst Gear 2.74:1
^ 2nd Gear 1.55:1
^ 3rd Gear 1.00:1
^ Reverse 2.20:1
HYDRAULIC SYSTEM
The hydraulic system consists of a single oil pump, a valve body containing the pressure regulating shift control and lockup control valves, a governor valve assembly, two band actuating servos and an accumulator.
FLUID COOLING AND FILTRATION
The transmission fluid is cooled by circulating the fluid through an external cooler built into the radiator lower tank.
Transmission fluid is filtered by a Dacron element filter attached to the valve body. The filter is a serviceable component and can be replaced whenever diagnosis or service requirements indicate that this should be done.
TRANSMISSION VENTING
The transmission is vented through a passage drilled into the upper portion of the oil pump housing.
TORQUE CONVERTER
The torque converter is a welded assembly and is not serviceable. If diagnosis indicates a malfunction has occurred or if the converter becomes contaminated with foreign material, replace the converter as an assembly only. Do not attempt to repair orflush the unit. In addition, never attempt to interchange lockup and conventional converters. The transmission input shaft and valve body required for lockup operation are markedly different.
TRANSMISSION CODE AND PART NUMBER IDENTIFICATION
Transmission Identification:
A seven-digit transmission part number (1) is stamped on the left side of the case just above the oil pan mating surface. This number is followed by a four-digit code number (2) which indicates date of manufacture.
The final four-digit number group stamped on the case represents the transmission serial number (3).
LOCKUP TORQUE CONVERTER IDENTIFICATION
Because the lockup mechanism is completely enclosed within the converter and not visible, lockup converters have an identifying decal attached to the front cover.
The decal is circular in shape and states converter type and stall ratios, such as Lockup and LS (low stall) or HS (high stall).