303F: Powertrain & Automatic Trans. Testing & Service Flashcards
What are the five basic steps to trouble shooting a power shift or automatic transmission?
- Gather information
- Talk to the operator
- Visual inspection
- Perform operational tests
- Testing using specialized test equipment
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What are three sources you can gather troubleshooting information from?
- Service manuals
- Service bulletins
- Operator’s manuals
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What is some typical information you can gather from talking to the operator as a step in the troubleshooting process?
- Working environment conditions
- Modifications to machine
- Repairs to machine
- Noises or erratic movements or other failures
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When performing operations tests, what is the first step that must be done to get an accurate assessment?
Oil must be at normal operating temperature.
150-180F
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How do you perform a torque converter stall test to help warm up oil?
- Lock the service and park brake
- Select highest possible speed range
- Run the engine at wide open throttle
- Record engine RPM on tachometer
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When warming up the oil prior to operational testing, how long should a stall test run for before cycling into neutral for cool down?
30 seconds to prevent overheating
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What can cause a low stall speed during a torque converter stall test?
- The engine is not producing sufficient power
- Torque converter stator is slipping
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What can cause high stall speed during a torque converter stall test?
- Engine is producing excessive power (over fuel)
- Clutches are slipping inside transmission
- Torque converter is cavitating (insufficient TC charge oil flow)
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When pressure testing a hydraulic system, what range should your gauges be?
Two times the expected pressure
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What are the hydraulic circuits in a powershift or automatic transmission shift system?
- Clutch application circuit
- Torque converter charge circuit
- Transmission lubrication circuit
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What would an extremely low transmission charge pump inlet pressure below 12 psia would mean?
A restriction on the pump inlet side
May result in cavitation
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How is cavitation in the transmission charge pump caused?
Restriction on the pump inlet line causing low pump inlet pressure
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Pressure readings at the transmission charge pump inlet are higher than normal. What could be the cause?
Air is being drawn into the pump inlet.
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Where do you have to place a pressure gauge to read available clutch application pressure in the transmission circuit?
Between the charge pump and clutch pressure regulator valve.
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How can you check for large internal leakage in the transmission clutch application circuit?
With engine running at high and low idle, clutch application pressure should be maintained.
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What could cause low pressure reading on the transmission torque converter charging circuit?
- Insufficient charge pump flow
- Excessive leakage in the clutch application circuit
- Excessive leakage in the torque converter circuit
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What could cause low transmission lubrication circuit pressure?
- Insufficient charge pump flow
- Excessive leakage in the clutch application circuit
- Excessive leakage in the lubrication circuit
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What two circuits provide the transmission with pressure signals which are used to control shift points?
Governor Circuit: Ground speed
Modulator Cicuit: Operator’s demand for power
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How are shift points manually adjusted in an automatic transmission?
Adjusting the spring tension on the shift signal valves
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How can the ECU be protected from high voltage or surges?
- Unplug the ECU while welding
- Do not use fast charges to start the engine
- Remove batteries to use fast charges
- Never disconnect the battery while engine is running
- Do not open electrical connections when system is operational or running
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What are some conditions that can be checked on transmission bearings and cast components durring dissasembly?
- Rough rotation
- Chipped races
- Defective bore mating surface
- Scoring
- Pitting
- Wear
- Cracks
- Damaged threads
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What should clutch friction discs be inspected for?
- Burrs
- Embedded metal particles
- Severely pitted friction materials
- Cracks and distortion
- Flaking friction material
- Damaged spline teeth
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What should clutch friction discs be measured for?
- Wear
- Warpage
- Cone
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How can you measure warpage and cone on a clutch friction disc?
Measured at three locations with a feeler blade while laying flat on a known flat surface
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Clearance between clutch discs can be altered by: (2)
- Installing a selective steel reation disc
- Installing a clutch piston of the correct thickness
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What important final check should be done after installing an engine mounted transmission?
Check crankshaft endplay
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