Honda Acura NSX 1991 Service Manual page 394

Description
The Acura four speed automatic transmission uses hydraulically actuated clutches to engage or disengage the transmission
gears. When clutch pressure is introduced into the clutch drum, the clutch piston is applied. This presses the friction
discs and steel plates together, locking them so they don't slip. Power is then transmitted through the engaged clutch
pack to its hub-mounted gear.
Likewise, when clutch pressure is bled from the clutch pack, the piston releases the friction discs and steel plates, and
they are free to slide past each other while disengaged. This allows the gear to spin independently of its shaft, transmitting
no power.
[I st Clutch1
The first clutch engages/disengages first gear, and is located at the end of the mainshaft, just behind the end cover.
The first clutch is supplied clutch pressure by its oil feed pipe within the mainshaft.
[I St-Hold Clutch]
The first hold clutch engages/disengages low hold or 1 position, and is located at the end of the countershaft, just behind
the end cover. The 1st hold clutch is supplied clutch pressure by its oil feed pipe within the countershaft.
Clutch1
The second clutch engages/disengages second gear, and is located on the secondary shaft. The second clutch is supplied
clutch pressure through the secondary shaft by a circuit connected to the 2nd accumulator body.
Clutch1
The third clutch engages/disengages third gear, and is located at the end of the countershaft, opposite the end cover
The third clutch is supplied clutch pressure by its oil feed pipe within the countershaft.
The fourth clutch engages/disengages fourth gear, as well as reverse gear, and is located at the center of the mainshaft.
The fourth clutch is supplied clutch pressure by its oil feed pipe within the mainshaft.
[One-way Clutch1
The one-way clutch is positioned between the parking gear and first gear, with the parking gear splined to the countershaft.
The first gear provides the outer race surface, and the parking gear provides the inner race surface. The one-way clutch
locks up when power is transmitted from the mainshaft first gear to the countershaft first gear.
The first clutch and gears remain engaged in the 1 st, 2nd, 3rd, and 4th gear ranges in the
one-way clutch disengages when the 2nd, 3rd, or 4th clutches/gears are applied in the IDI position. This is because the
increased rotational speed of the gears on the countershaft over-ride the locking "speed range" of the one-way clutch.
Thereafter, the one-way clutch freewheels with the first clutch still engaged.
COUNTERSHAFT IST GEAR
L O C K S
FREE
PARKING GEAR
q
position. However, the