1956 AMC Hudson Technical Service Manual Supplement

HYDRA-MATIC TRANSMISSION 101
TESTING AND DIAGNOSIS
"STALL" OR TORQUE TEST
A "Stall" or Torque test may be made to determine
engine and transmission performance. This test must be
used with moderation because considerable strain is
exerted on the drive line, differential gears, and axles.
To perform "Stall" test, proceed as follows:
Start engine and warm up to operating temperature.
Connect electric tachometer.
Set hand brake lever tightly and apply foot brake
firmly.
Place selector lever in "D" position.
Depress accelerator pedal to floor.
Action has placed transmission in first speed. Brakes
are applied, therefore the car cannot move. Opening the
throttle and speeding up the engine is comparable to
slipping a mechanical clutch, as the driving torus is
turning and trying to turn the driven torus which is held
stationary by the transmission being in first speed and
brakes locked.
The engine will speed up until the friction created
between the torus members equals the power output of
the engine. Engine speed will denote efficiency and
should compare to specifications outlined in Figure 146.
If engine R.P.M. is less than the low limit, the engine
is in need of a tune-up.
If engine continues to speed up to approximately 200
to 350 R.P.M. above the high limit, it indicates that
clutch sprags are not holding properly or that there is
slippage in fluid coupling, damaged torus members, or
defective front pump.
CAUTION: Extreme care must be used in making
this test. DO NOT HOLD THROTTLE OPEN
MORE THAN ONE MINUTE. If engine speeds up
to 350 R.P.M. over specifications, close throttle
immediately to avoid possible damage to transmission.
Sometimes, it is desirable to know which unit is
slipping. After making test with selector lever in "D"
position, place lever in "R" position and test again. If
slippage still occurs, fault is with front unit or both. If
slippage does not occur, then all slippage is in the rear
unit. Since this transmission starts in 1st speed in "L"
range, the stall speed should be exactly the same in "L"
range as it is in Drive and Reverse.
Check Cause for Slipping Under "Stall Test"
Set hand brake lever tightly.
Start engine and run at a speed equivalent to 20 M.P.H
for approximately 11/2 minutes. Then, with engine
IDLING, selector lever in "N" range, check the fluid
level in the transmission.
See that fluid is at the "Full" mark on the indicator.
After level has been checked, shut off engine and
wait 10 minutes. If the fluid level in the transmission
has not raised more than 1/2", the driven torus check
valve is operating satisfactorily.
If check valve is operating satisfactorily, road test
car using Diagnosis Guide.
OIL PRESSURE TEST
Connect oil pressure gauge j-2540 to take-off hole at
bottom of rear pump using hose and fitting.
Start engine and operate for several minutes to warm
transmission oil to normal operating temperature
(approx. 175°F.).
When transmission is thoroughly warm, check pressure
in all ranges. Pressure should be 50 lbs. minimum
in "P," "N," D-4, D-3, and "L" ranges with a maximum
variation of 10 lbs. between ranges. The pressure,
however, may be higher in reverse.
Check pressure in D-3 position at approximately 25
M.P.H. while driving car. Pressure should be 90-100
P.S.I.
NOTE: Pressure at any speed is constant regardless
of throttle position. T.V. pressure is
not used to modulate line pressure.
While driving at 25 M.P.H., move selector lever
back to D-4 position so transmission will shift into
fourth speed. Oil pressure should drop to 60-70 P.S.I.
in fourth speed.
NOTE: To reduce the amount of work done by
the front pump, pressure is directed from the
3-4 shift valve to the pressure regulator to
reduce line pressure in fourth speed when in
D-4 position. In D-3 position, line pressure
remains at 90-100 P.S.I. in fourth speed.
To check pressure in reverse, stop car and set hand
brake firmly. Then place selector lever in "R" range
and apply foot brake and open accelerator to half
throttle. Pressure should increase to 145-190 P.S.I.
Diagnosis of malfunctions can frequently be aided
by noting oil pressure under all operating conditions
while driving on the road.
ROAD TEST
A road test can be made using the shift speed chart in
Figure 146. It will be observed, however, that the
closed throttle downshifts in D-4 and the 3-2 downshift
in D-3 cannot be distinguished. The reason is that in
D-4, the sprags in both