The HYDRA-MATIC 440-t4 is a fully automatic front wheel drive transaxle. It provides four forward range including overdrive.
The major components of this unit are:
* Torque Converter with converter clutch
* sprocket and drive link assembly
* 1-2 and reverse band assemblies
* Input, 3rd, 2nd, and 4th clutch - multiple disc assemblies
* Input sprag and 3rd roller clutch
* compound planetary gear set
* Differential and final drive assembly
Oil pressure is supplied by a variable vane type oil pump. the oil pressure is regulated by vacuum modulation and shift points are controlled by throttle opening via a throttle valve cable and a governor circuit.
Garage Shift Check
1. Start engine.
2. Depress Brake pedal.
3. Move gear selector:
* "park"(P) to "reverse" (R)
* "Reverse" (R) to "Neutral" (N) to "Overdrive" (D4)
Gear selector should be immediate and not harsh.
IMPORTANT: The torque converter clutch will not engage if engine coolant has not reached a minimum operation temperature of approximately 54 degree C (130 degree F)
UPSHIFTS AND TORQUE CONVERTER CLUTCH (TCC) APPLY
with gear selector in "Overdrive" (D4):
1. Accelerate using a steady increasing throttle pressure.
2. Not the shift speed point gear engagement for:
* 2nd gear
* 3rd gear
3. Not the speed shift point for TCC apply. This should occur while in third gear or Overdrive. If the apply is not noticed, converter may be faulty
PART THROTTLE DETENT DOWNSHIFT
* At vehicle speed of 40-55 mph (64-88 km/h) quickly depressed the accelerator to a half open position and observe:
* TCC releases (engine rev)
* Transaxle downshift to 3rd gear immediately
FULL THROTTLE DETENT DOWNSHIFT
* At vehicle speeds of 40-55mph (64-88Km/h) quickly depress throttle to wide open position and observe:
* TCC releases
* transaxle downshift to 2nd gear immediately
1. At vehicle speed of 40-55 mph (64-88 km/h) release the accelerator pedal while moving the gear selector to "third"(D3) gear and observe:
* TCC release
* Transaxle downshift to 3rd gear should be immediate
* Engine should slow vehicle down
Repeat (1.) for each gear selector and observe the same action.
TRANSAXLE FLUID LEVEL INFORMATION
Check fluid level, color and condition at regular intervals will provide early diagnosis information about the transaxle. This information may the be used to correct a condition that, if not detected early, could result in major transaxle repairs.
When adding or CHANGING FLUID, us only DEXRON II ( i was told type F fluid will give a firmer shift, because Type F fluid has less lube/slipping additive. GM DEXRON II allow slippage of clutches to provide a soft shift) or equivalent.
* fluid level should be check when it reaches normal operation temperature of 88 to 93 degrees C. this temperature is reached after approximately 15 miles of highway driving.
* Fluid color should be dark red (may be dark brown, require fluid and filter change)
NOTICE: Do not overfill. Overfilling will cause foaming, loss of fluid and possible damage to the transaxle.
* Inaccurate fluid level reading will result if checked immediately after the vehicle has been operated:
* in temperature above 90 degrees F (32C)
* at sustained high speeds.
* In heavy city traffic during hot weather.
* as a towing vehicle.
* In commercial service (taxi or police use)
VACUUM MODULATOR SYSTEM
The vacuum modulator system controls shift feel (harshness) by sensing changes in engine load, which is indicated by engine vacuum. the modulator does this by controlling main line pressure boost. the vacuum modulator system may be suspect for harsh or slipping shift condition.
Sources: GM SERVICE MANUAL
Wiki Authors: SteveX
Dates Modified: 4-28-08
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