Ford Explorer, Руководство по техническому обслуживанию и ремонту

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MANUAL TRANSMISSION
Understanding the Manual Transmission
Because of the way an internal combustion engine breathes, it can produce torque (or twisting force) only
within a narrow speed range. Most overhead valve pushrod engines must turn at about 2500 rpm to produce
their peak torque. Often by 4500 rpm, they are producing so little torque that continued increases in engine
speed produce no power increases.
The torque peak on overhead camshaft engines is, generally, much higher, but much narrower.
The manual transmission and clutch are employed to vary the relationship between engine RPM and the speed
of the wheels so that adequate power can be produced under all circumstances. The clutch allows engine
torque to be applied to the transmission input shaft gradually, due to mechanical slippage. The vehicle can,
consequently, be started smoothly from a full stop.
The transmission changes the ratio between the rotating speeds of the engine and the wheels by the use of
gears. 4−speed or 5−speed transmissions are most common. The lower gears allow full engine power to be
applied to the rear wheels during acceleration at low speeds.
The clutch driveplate is a thin disc, the center of which is splined to the transmission input shaft. Both sides of
the disc are covered with a layer of material which is similar to brake lining and which is capable of allowing
slippage without roughness or excessive noise.
The clutch cover is bolted to the engine flywheel and incorporates a diaphragm spring which provides the
pressure to engage the clutch. The cover also houses the pressure plate. When the clutch pedal is released, the
driven disc is sandwiched between the pressure plate and the smooth surface of the flywheel, thus forcing the
disc to turn at the same speed as the engine crankshaft.
The transmission contains a mainshaft which passes all the way through the transmission, from the clutch to
the driveshaft. This shaft is separated at one point, so that front and rear portions can turn at different speeds.
Power is transmitted by a countershaft in the lower gears and reverse. The gears of the countershaft mesh with
gears on the mainshaft, allowing power to be carried from one to the other. Countershaft gears are often
integral with that shaft, while several of the mainshaft gears can either rotate independently of the shaft or be
locked to it. Shifting from one gear to the next causes one of the gears to be freed from rotating with the shaft
and locks another to it. Gears are locked and unlocked by internal dog clutches which slide between the center
of the gear and the shaft. The forward gears usually employ synchronizers; friction members which smoothly
bring gear and shaft to the same speed before the toothed dog clutches are engaged.
Identification
The Ranger and Explorer trucks had two manual transmission available, depending on the engine. The Mazda
M5OD 5−speed overdrive transmission came equipped on both the 4x2 and 4x4 versions. The Mitsubishi
5−speed overdrive transmission only came on the 2.9L equipped 4x4 Ranger vehicles from 1991−92.
Adjustments
MANUAL TRANSMISSION 755