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Flashcards in Powershift Control and Shifting Deck (31):

Typical clutch application pressures range from

100 - 500 PSI


Typical Lube pressure

30-50 PSI


TC relief valve

Located in parallel to the inlet of the TC, dumps directly bank to sump
Used to limit max pressure in the TC


Typical TC charge presure

50-125 PSI


Lube relief valve

Controls the max lube pressure, usually located after cooler and before oil get to lube components


What are the 4 pumps located in the powershift oil pump group

Transmission scavenging pump
TC/TD scavenging pump
Transmission charging pump
Steering and Brake lube pump


Trans Shift Selector - Load piston

Controls the rate of pressure rise in the clutch pistons
Called shift modulation and is done to prevent shift shock, and clutch slippage


Trans Shift Selector - Pressure differential valve

Controls which clutch will apply first (F/R or 123)


TC outlet relief valve

Limits the maximum working pressure in the TC. Spool is usually identical in size on both sides, so it has a pilot drilling to allow oil to enter opposite side of spring to create pressure diff.


Valve spring cavities

Almost all control spring cavities have a drain back to tank to prevent oil from getting trapped


Trans oil cooler

Long tubes inside for coolant to travel through is called straw type cooler
located following TC


The 3 hydraulic circuits in a basic shift control system are

Clutch application circuit
Converter charging circuit
Trans lube circuit


Oil flow for trans control system operation is supplied by

Charging pump driven at engine speed


In a basic hydraulic shift control system, speed and direction changes are made by the

Shift selector valve


The function of the clutch pressure regulator valve is to

Limit the application pressure applied to the clutch pistons


The circuit that receives oil flow after the clutch application circuit has been satisfied is the

Converter charging circuit


Maximum pressure in the TC is controlled by

TC relief valve


What is the function of a trans scavenge pump (if equipped)

Remove leakage oil from the trans case


Clutch modulation refers to

Controlling the build up of pressure in the clutch piston allowing controlled slippage of the clutch discs


The factors that influence the point at which an automatic transmission shift are

Machine ground speed
Operator demand for power


Modulator circuit

Is used to alter the shift points of the transmission in relation to the operator demand for power


Modulator valve operation

When greater power demand is called for the cable moves tapered end reducing the spring pressure created in valve, this means instead of adding 50 psi (EX) to help governor it adds closer to zero meaning that vehicle speed has to be increased to raise governor pressure to make next upshift


4 types of shift dampening devices

orifice control


Orifice control shift dampening

Commonly used to control clutch release rates
placed in line between relay valve and sump to slow the rate at which springs push oil back


Trimmer valve shift dampening

When pressure starts to develop in clutch a piston in valve moves allowing some oil to go to sump, as pressure move through orifice in piston, piston is pushed back up and sump port is blocked again continuing to fill clutch


The function of the governor circuit in auto trans is

Provide a hydraulic signal that is proportional to machine ground speed


Governor flyweights balance against what

Governor pressure


How are shift point normally adjusted in auto trans

By varying the shift signal valve spring force


The function of the modulator circuit is what

Provide a hydraulic signal that is proportional to the position of the engine throttle, this pressure is used to delay shift points when throttle is wide open


4 functions of the ECU in an electronically controlled shift system

Control up and down shifts
Control clutch modulation
Provide diagnostic info
Provide warning to operator when malfunction occurs


What output device is responsible for causing speed and direction changes

Shift solenoids