- Torque converter
- A fluid coupling between the engine and transmission that multiplies engine torque at low speed and contains a lock-up clutch for direct drive at cruise.
- Lock-up clutch
- A clutch inside the torque converter that mechanically couples the impeller to the turbine, eliminating slip to improve fuel economy at cruising speed.
- Impeller (pump)
- The torque converter element driven by the engine that flings fluid outward to drive the turbine.
- Turbine
- The torque converter element connected to the transmission input shaft; fluid from the impeller spins it to transmit power.
- Stator
- The torque converter element that redirects returning fluid to multiply torque; it rides on a one-way clutch.
- Stator one-way clutch
- An overrunning clutch that holds the stator during torque multiplication and lets it freewheel at the coupling point.
- Planetary gearset
- A gear arrangement of a sun gear, planet pinions on a carrier, and a ring gear that provides the transmission's forward, reverse, and reduction ratios.
- Sun gear
- The central gear of a planetary gearset; holding or driving it produces different gear ratios.
- Ring gear (annulus)
- The outer internally toothed gear of a planetary set that meshes with the planet pinions.
- Planet carrier
- The member that holds the planet pinions; output through the carrier yields gear reduction.
- Valve body
- The hydraulic control center of the transmission, containing valves and passages that route fluid pressure to apply clutches and bands for shifts.
- Shift solenoid
- An electrically operated valve that the TCM/PCM uses to direct hydraulic pressure for automatic up- and downshifts.
- Pressure control solenoid (EPC)
- A solenoid that varies line pressure electronically based on throttle load and torque to control shift feel and clutch apply.
- Line pressure
- The base hydraulic pressure produced by the pump and regulated by the pressure regulator valve; it supplies all apply circuits.
- Pressure regulator valve
- The valve that sets line pressure by bleeding off excess pump output back to the sump or converter circuit.
- Governor pressure
- In hydraulically controlled transmissions, a road-speed-proportional pressure that helps schedule upshifts (replaced by VSS data in electronic units).
- Throttle (TV) pressure
- A pressure proportional to engine load used in older transmissions to delay shifts under acceleration; modern units use throttle-position sensor data.
- Stall test
- A diagnostic that holds the brakes and briefly applies full throttle in gear to read converter stall speed, checking the converter and clutch/band holding capacity.
- Stall speed
- The maximum engine rpm reached during a stall test; high or low readings point to converter, clutch, or band problems.
- Pressure test
- Connecting a gauge to a test port to measure line and circuit pressures and compare them against specification across gear ranges.
- Air pressure test
- Applying regulated shop air to valve-body circuits to confirm a clutch or band applies, isolating hydraulic versus mechanical faults.
- Road test
- A controlled drive that checks shift timing, quality, slip, harshness, and noise through all ranges to characterize a complaint.
- Shift quality
- The smoothness and timing of a gear change; harsh, slipping, or delayed shifts indicate pressure, clutch, or control faults.
- Slipping
- A condition where engine rpm rises without a matching increase in vehicle speed, caused by worn clutches/bands, low fluid, or low pressure.
- Flare (shift flare)
- A momentary rpm rise during a shift caused by one element releasing before the next applies; a sign of worn clutches or low pressure.
- Harsh engagement
- An abrupt, firm shift or Park-to-Drive engagement, often from high line pressure, a faulty EPC solenoid, or a converter fault.
- Delayed engagement
- A lag between selecting a gear and the vehicle moving, commonly from low fluid, internal leaks, worn pump, or worn clutch seals.
- Shudder
- A vibration felt during torque-converter lock-up apply, frequently caused by contaminated fluid or a worn lock-up clutch.
- Burnt fluid
- ATF that is dark and smells burnt, indicating overheated, slipping friction material and likely internal clutch/band damage.
- Milky/foamy fluid
- ATF that is pink and milky from coolant or water contamination, often a failed transmission cooler in the radiator.
- Limp-in mode (failsafe)
- A protective strategy where the TCM locks the transmission into one gear after detecting an electronic fault to allow limited driving.
- Diagnostic trouble code (DTC)
- A stored code the TCM/PCM sets when an input or output is out of range, retrieved with a scan tool to direct diagnosis.
- Scan tool
- A device that reads DTCs, live data, and bidirectional commands from the transmission controller to verify sensors and actuators.
- Transmission control module (TCM)
- The computer that monitors sensors and operates shift solenoids to control shift timing, pressure, and converter lock-up.
- Vehicle speed sensor (VSS)
- A sensor that reports output/road speed to the TCM for shift scheduling and speedometer operation.
- Input/turbine speed sensor
- A sensor measuring input shaft speed; comparing it to output speed lets the TCM detect slip and control shift feel.
- Transmission range sensor (TR/PRNDL)
- A switch/sensor that tells the controller which gear range the shifter selects and enables starter only in Park/Neutral.
- Transmission fluid temperature (TFT) sensor
- A thermistor that reports ATF temperature so the TCM can adjust line pressure, lock-up, and overheat protection.
- Throttle position sensor (TPS)
- A sensor of throttle/load the TCM uses to schedule shift points and shift firmness.
- Manual valve
- The valve in the valve body moved directly by the gear selector linkage to route pressure for the chosen range.
- Accumulator
- A spring-and-piston device that cushions clutch/band apply for smoother shifts by temporarily absorbing apply pressure.
- Servo
- A hydraulic piston that applies a band when fed apply pressure from the valve body.
- Band
- A friction-lined steel strap that wraps and holds a drum stationary to provide a reaction member for certain gears.
- Clutch pack
- Alternating friction and steel plates that lock rotating members together when apply pressure compresses them.
- One-way (overrunning) clutch
- A mechanical clutch that drives in one direction and freewheels in the other, providing automatic holding for certain gears.
- No-movement (no drive)
- A condition where the vehicle will not move in any range, often from low fluid, a failed pump, broken input shaft, or stripped splines.
- No reverse
- Loss of reverse only, usually a specific clutch/band, servo, or valve-body circuit dedicated to reverse.
- Erratic/hunting shifts
- Random or repeated shifting between gears, commonly from a faulty speed sensor, solenoid, or internal leak.
- Converter clutch shudder vs. engine misfire
- Shudder only during lock-up apply points to the converter clutch; shudder under load in any gear points to the engine.
- Cross-leak
- Internal fluid leakage between circuits past worn seals or a warped valve body that causes slipping or wrong gear apply.
- Automatic transmission fluid (ATF)
- A specialized hydraulic oil that transmits power, cools, lubricates, and provides correct friction for clutches and bands.
- ATF specification
- The exact fluid type a transmission requires (such as DEXRON, MERCON, or a CVT/DCT fluid); using the wrong fluid causes shift faults and damage.
- Fluid level check
- Verifying ATF level, usually at operating temperature on a level surface with the engine running and selector cycled, per the service procedure.
- Hot vs. cold fluid level
- ATF expands with heat, so the dipstick has separate hot and cold ranges; reading at the wrong temperature gives a false level.
- Fluid condition inspection
- Judging ATF by color and smell: bright red is good; brown/burnt signals overheating; milky signals coolant contamination.
- Transmission fluid change
- Draining and refilling ATF and replacing the filter at the service interval to remove worn friction material and restore additives.
- Transmission flush
- A machine procedure that exchanges nearly all old fluid; only appropriate when the manufacturer approves it for that unit.
- Transmission filter
- A screen or media filter on the pump pickup that removes debris; replaced during a fluid/pan service.
- Transmission pan
- The bottom cover that holds reserve fluid; debris in the pan (metal, clutch material) is a key diagnostic clue.
- Pan gasket
- The seal between the pan and case; replaced during service and torqued evenly to prevent leaks.
- Magnet (pan magnet)
- A magnet in the pan that collects ferrous wear particles; heavy steel debris indicates internal gear or bearing failure.
- Transmission cooler
- A heat exchanger (in the radiator or a separate cooler) that removes heat from ATF to prevent overheating.
- Cooler line
- Steel or rubber lines carrying ATF between the transmission and cooler; cracks or leaks cause fluid loss and overheating.
- Cooler flush
- Cleaning the cooler and lines of debris after an internal failure so contamination is not returned to a rebuilt unit.
- Oil pump
- The transmission's pump (gear or rotor type) driven by the converter that generates the line pressure all hydraulics depend on.
- Foaming (aeration)
- Air whipped into ATF from overfill or low level that compresses, causing erratic pressure, slipping, and overheating.
- Overfill
- Too much ATF, which lets rotating parts churn the fluid into foam and raises temperatures.
- Underfill (low fluid)
- Too little ATF, causing pump aeration, low pressure, slipping, delayed engagement, and overheating.
- Pressure test port
- A threaded port on the case where a gauge connects to read line or circuit pressure during diagnosis.
- Band adjustment
- Setting band apply clearance to specification (often a torque-and-back-off procedure) so the band holds without dragging.
- Shift linkage adjustment
- Aligning the selector linkage or cable so the manual valve fully seats in each range and the indicator matches the gear.
- Neutral safety switch
- A switch (often the range sensor) that allows cranking only in Park or Neutral and enables the reverse lamps.
- Throttle/TV cable adjustment
- Setting the throttle-valve cable so shift timing and firmness match load in cable-controlled transmissions.
- Valve-body service (in-vehicle)
- Removing and cleaning or replacing the valve body or solenoids with the transmission still in the vehicle to fix hydraulic faults.
- Solenoid replacement (in-vehicle)
- Swapping a faulty shift or pressure-control solenoid through the pan without removing the transmission, when accessible.
- Speed sensor replacement
- Replacing an input or output speed sensor that is causing erratic shifts or speedometer faults.
- Extension housing seal
- The rear seal around the output shaft/yoke; a common external leak point serviceable in the vehicle.
- Axle/output shaft seal
- On a transaxle, the seal where a drive axle enters the case; a frequent in-vehicle leak repair.
- Manual shaft seal
- The seal where the selector shaft enters the case; leaks here are repaired in the vehicle.
- Speedometer drive/sensor seal
- The seal at the vehicle-speed sensor or drive that can leak and is replaced in the vehicle.
- Front pump seal
- The seal at the converter snout/pump; a leak here usually requires removing the transmission to access.
- Leak diagnosis (dye)
- Adding UV dye to ATF and using a UV light to pinpoint the exact source of an external leak.
- Converter drain-back
- Loss of converter fluid into the pan after shutdown that causes a brief delayed engagement on the next start.
- External leak vs. internal leak
- External leaks lose fluid to the ground; internal leaks pass fluid between circuits, causing slipping without visible loss.
- Reprogramming/relearn (in-vehicle)
- Flashing TCM software or performing an adaptive relearn after service so shift adapts match the current hardware.
- Adaptive learning
- The TCM's running adjustment of clutch apply timing/pressure to compensate for wear, which may need resetting after repairs.
- Transmission mount
- A rubber/hydraulic mount supporting the transmission; a worn mount causes clunks and driveline vibration.
- Cooler bypass/thermostat
- A valve that warms ATF quickly by limiting cooler flow until temperature rises, then opens for cooling.
- Quick-connect cooler fitting
- A push-to-connect cooler line fitting requiring a special tool and care to avoid leaks during service.
- Fluid fill procedure
- Adding the specified ATF type and quantity, then verifying level at the correct temperature with the engine running.
- Transmission jack
- A specialized jack with a cradle and safety chains used to lower, support, and raise the heavy transmission during R&R.
- Transmission holding fixture
- A bench fixture that clamps the case so the unit can be rotated and disassembled safely on the bench.
- Converter removal
- Sliding the torque converter straight off the input shaft after R&R so it does not fall and to inspect/replace it.
- Flexplate (flywheel)
- The thin steel plate bolting the converter to the crankshaft; inspected for cracks and worn ring-gear teeth during R&R.
- Converter bolt torque
- Tightening the converter-to-flexplate bolts evenly to specification to prevent vibration and bolt failure.
- Input shaft
- The shaft driven by the converter turbine that delivers power into the gear train; inspected for worn splines and twist.
- Output shaft
- The shaft delivering power out of the transmission; checked for wear, runout, and damaged splines.
- End play
- The controlled axial free movement of the geartrain, set with selective washers and measured with a dial indicator.
- End-play gauge / dial indicator
- A tool that measures axial geartrain movement so the correct selective thrust washer can be installed.
- Selective washer/snap ring
- A thrust washer or snap ring chosen by thickness to bring end play within specification during reassembly.
- Feeler gauge
- A set of precise blades used to measure clutch-pack clearance, band clearance, and other small gaps.
- Clutch clearance (pack clearance)
- The measured gap in an apply clutch pack, set with selective plates/pressure plates so the clutch applies and releases correctly.
- Air-check (clutch apply test)
- Applying shop air to a clutch circuit during reassembly to confirm the piston strokes and seals hold.
- Friction (clutch) plate
- A plate lined with friction material that grips steel plates when the clutch applies; inspected for burning, glazing, and wear.
- Steel (reaction) plate
- A bare steel plate alternating with friction plates; checked for heat discoloration, warpage, and scoring.
- Pressure plate
- The thick plate that backs a clutch pack; its thickness can be selective to set clutch clearance.
- Clutch piston / seals
- The hydraulic piston and its lip/O-ring seals that apply a clutch; replaced during overhaul to restore apply pressure.
- Bushing
- A plain bearing supporting a rotating shaft or drum; inspected for wear, scoring, and excess clearance during overhaul.
- Thrust bearing/washer
- A bearing or washer that controls axial loads between rotating members; wear here increases end play and noise.
- Needle (Torrington) bearing
- A flat caged needle bearing used between geartrain members to handle thrust loads with low friction.
- Sealing rings
- Metal or Teflon rings on shafts and drums that seal rotating hydraulic circuits; inspected and replaced on overhaul.
- Pump (off-vehicle) inspection
- Measuring pump gear/rotor clearances and checking the pump body for wear that would lower line pressure.
- Pump clearance measurement
- Using a feeler gauge to check gear-tip, side, and body clearances against spec to confirm pump condition.
- Valve-body inspection
- Cleaning the valve body and checking valves for free movement, scoring, and a warped mating surface that causes cross-leaks.
- Separator plate
- The plate with calibrated orifices between valve-body halves; checked for wear, wrong orifices, and proper gasket alignment.
- Case inspection
- Examining the aluminum case for cracks, stripped threads, worn bores, and damaged sealing surfaces before reassembly.
- Bearing preload
- The controlled load set on tapered bearings (in some transaxles/final drives) to remove play without overloading.
- Backlash (final drive)
- The play between final-drive/differential gears, measured and adjusted with shims in transaxle service.
- Differential (transaxle)
- The final-drive gear unit inside a transaxle that splits power to the drive axles and allows wheel speed difference.
- Final drive gear
- The reduction gearset in a transaxle that transmits geartrain output to the differential.
- Drum inspection
- Checking clutch drums for cracks, worn band surfaces, scored bushing bores, and damaged sealing-ring grooves.
- Snap-ring pliers
- A tool for removing and installing the snap rings that retain clutch packs, servos, and pump components.
- Seal protector / installer
- A sleeve and driver set used to install lip seals and rings without cutting or rolling them.
- Assembly lubricant
- Petroleum jelly or ATF-based lube used to hold thrust washers in place and pre-lube seals during reassembly.
- Torque specification
- The manufacturer-specified tightening value for case bolts, pump bolts, and the converter, applied in the correct sequence.
- Geartrain blow-down/cleaning
- Cleaning all parts in solvent and drying with compressed air before inspection so debris and contamination are removed.
- Initial fill and prime
- Adding ATF and rotating/cycling the unit after install to prime the pump and purge air before the first drive.
- Converter installation depth
- Verifying the converter is fully seated on the pump and stator splines before bolting to the flexplate to avoid pump damage.
- Dowel pin alignment
- Using case dowels to align the transmission to the engine block during installation so the bellhousing seats squarely.
- Road test after overhaul
- A final verification drive checking shift quality, lock-up, and the absence of leaks and noise after reinstallation.
- Transaxle
- A combined transmission and final-drive/differential in one housing, used in front-wheel-drive and some rear/mid-engine vehicles.
- Hydraulic principle (Pascal's law)
- Pressure applied to a confined fluid acts equally in all directions, the basis for transmission clutch and band apply.
- Torque multiplication
- The converter's ability to increase engine torque at low turbine speed thanks to the stator redirecting fluid.
- Coupling point
- The speed at which turbine nearly matches impeller, torque multiplication ends, and the converter acts as a fluid coupling.
- Hydraulic vs. electronic control
- Older transmissions schedule shifts purely with governor/TV pressure; modern units use the TCM, sensors, and solenoids.
- CVT (continuously variable transmission)
- A transmission using a belt or chain between variable-diameter pulleys to provide infinite ratios rather than fixed gears.
- Dual-clutch transmission (DCT)
- An automated manual using two clutches (odd/even gears) for fast, smooth shifts under computer control.
- Kickdown
- A forced downshift commanded by full or near-full throttle to provide acceleration, via cable, switch, or TPS.
- Manual low / gear hold
- Selecting a low range to hold a lower gear for engine braking or grade climbing instead of allowing automatic upshifts.
- Park pawl
- A pin that locks into the output gear to hold the vehicle in Park; a worn pawl or linkage can let the vehicle roll.
- ATF cooler line routing
- Correct routing and connection (out/return) of cooler lines so flow direction matches the transmission requirement.
- Cross-leak (valve body warpage)
- Pressure leaking between circuits past a warped valve-body face or worn separator plate, causing slip or wrong-gear apply.
- Selective thrust washer chart
- The service chart relating measured end play to the thrust-washer thickness needed to bring it into spec.
- Burnishing (new clutches)
- Controlled break-in cycles after overhaul that seat new friction material for proper holding and shift feel.
- Fluid coupling
- A torque converter operating without multiplication, transmitting power as a simple fluid coupling near the coupling point.
- Garage shift (engagement)
- The Park-to-Drive or Park-to-Reverse engagement; harshness or delay here is a key diagnostic symptom.
- Bump/clunk on engagement
- A jolt selecting a gear, from high line pressure, worn mounts, excessive driveline lash, or a faulty EPC solenoid.
- Overheating
- Excessive ATF temperature from heavy towing, low fluid, slipping, or a blocked cooler that rapidly degrades fluid and friction material.
- Filter restriction
- A plugged filter that starves the pump, causing low pressure, slipping, and a whining pump under load.
- Pump cavitation
- Air or vapor bubbles forming at the pump from a restricted pickup or low fluid, causing noise and pressure loss.
- Lip seal
- A flexible seal with a sealing lip used on pistons and shafts; installed with the lip facing apply pressure.
- O-ring seal
- A round-section rubber seal used in grooves to seal static or slow-moving hydraulic joints in the transmission.
- Wave/cushion plate
- A spring steel plate in a clutch pack that cushions initial apply for a smoother engagement.
- Return spring (clutch)
- The spring(s) that release a clutch piston when apply pressure drops, allowing the pack to disengage.
- Drive shell / input drum
- A rotating member transmitting power to a planetary element; inspected for cracks and worn splines on overhaul.
- Governor
- A speed-sensitive valve in hydraulic transmissions that generates road-speed-based pressure to schedule upshifts.
- Detent (kickdown) valve
- A valve that, at wide-open throttle, signals a downshift for passing in hydraulically controlled units.
- Modulator (vacuum)
- A vacuum-operated device on older transmissions that adjusts shift pressure with engine load via manifold vacuum.
- Vacuum modulator diagnosis
- Checking for ATF in the vacuum line, which indicates a ruptured modulator diaphragm drawing fluid into the intake.
- Shift feel calibration
- Tuning apply pressure and solenoid timing so shifts are firm enough to protect clutches yet smooth for the driver.
- Pressure rise (load)
- Line pressure increasing with throttle/torque so clutches hold under load; failure to rise causes slip under acceleration.
- Converter clutch apply/release
- The TCM commanding lock-up on and off based on speed, load, and temperature; faults cause stall, shudder, or poor economy.
- Stall test cautions
- Limiting each stall test to a few seconds and watching temperature to avoid overheating the converter and fluid.
- TFT-based protection
- The TCM inhibiting lock-up or reducing load when fluid temperature is too high or too low for proper operation.
- Wrong-fluid damage
- Using an incorrect ATF (friction modifier mismatch) causing shudder, harsh or slipping shifts, and accelerated wear.
- Cooler thermostat fault
- A stuck cooler-bypass valve causing overheating (stuck closed) or slow warm-up and poor economy (stuck open).
- Pump bushing wear
- Worn pump bushing causing converter-hub wear, low pressure, and a front-pump leak; found during off-vehicle inspection.
- Drum runout/warpage check
- Measuring drum surfaces for runout and warpage so bands and clutches seat correctly.
- Bearing endplay shim
- A shim selected to set tapered-bearing preload/endplay in transaxle final drives during reassembly.
- ASE A2 certification
- The ASE Automatic Transmission/Transaxle test for automotive technicians, part of the Automobile (A-series) certification.
- ASE recertification interval
- ASE certifications are valid for five years; technicians must pass a recertification test to maintain credentials.
- Pretest (unscored) items
- Trial questions mixed into an ASE test that gather statistics and do not count toward the score.
- ASE scored questions (A2)
- The A2 test contains roughly 50 questions, with about 45 scored items distributed across the content areas.
- Technician A / Technician B item
- An ASE question format where two technicians make statements and you decide which one(s) are correct.
- Driveline angle / vibration
- Incorrect driveline or mount alignment after R&R causing vibration mistaken for a transmission fault.
- Reverse-circuit clutch/band
- The specific apply device for reverse; its failure causes loss of reverse while forward gears remain.
- Wrong-gear start (limp)
- Starting in a high gear due to a failsafe or solenoid fault, producing sluggish, slipping launch.
- Surge / busy shifting
- Repeated small shifts or torque-converter cycling, often from a marginal speed sensor, solenoid, or low fluid.
- Aeration vs. contamination
- Foam from air (level/leak) versus milky fluid from coolant; the cause and fix differ, so identify which is present.
- Final road-test checklist
- Verifying correct fluid level, leak-free operation, full shift range, lock-up function, and no codes after any major repair.
- Snap-ring groove damage
- Worn or distorted snap-ring grooves in drums or the case that prevent proper retention of clutch packs and must be inspected.
- Lube circuit
- The low-pressure oil path that cools and lubricates the geartrain after pressure-regulator bleed-off; a blockage causes bearing failure.
- Cooler return filter
- An inline filter on the cooler return line that protects a rebuilt unit from debris left in the cooler system.
- Solenoid resistance test
- Measuring a solenoid's coil resistance against spec to confirm it is electrically sound before condemning the valve body.
- Wiring/connector inspection
- Checking the transmission's external harness and case connector for corrosion or opens that mimic internal electronic faults.
- Ground/voltage drop test
- Verifying clean power and ground to the TCM and solenoids, since high resistance can cause erratic, code-setting behavior.
- Quick-learn / fast adapt
- A scan-tool routine that resets and relearns shift adapts after a valve-body or transmission replacement.
- Converter balance/runout
- Checking converter pilot runout and balance after install to prevent vibration and flexplate cracking.
- Bellhousing alignment
- Verifying bellhousing-to-crank concentricity so the input shaft and converter are not loaded off-center.
- Input shaft seal rings
- Sealing rings on the input shaft that seal the apply circuits feeding the forward clutches; inspected on overhaul.
- Wear-particle analysis
- Judging the type of debris (friction material, bronze, steel) in the pan to identify which component failed.
- Cooler flow test
- Measuring ATF flow at the cooler return to confirm the pump, cooler, and lines are not restricted.
- Reverse/neutral lockout
- Hydraulic and electronic features that prevent reverse engagement above a set speed to protect the geartrain.
- Slip RPM monitoring
- The TCM comparing input and output speed to compute converter or clutch slip and detect early failure.
- Manual selector indicator
- The PRNDL display; a mismatch with the actual gear points to range-sensor or linkage misadjustment.
- Torque-converter stator slip
- Improper stator one-way clutch operation: seized stator causes poor high-speed performance; freewheeling stator causes weak acceleration.
- Pressure-regulator bore wear
- Wear in the regulator valve bore that lets line pressure fall off, causing general slipping under load.
- Accumulator piston/seal
- The accumulator piston and seal that cushion apply; a stuck or leaking accumulator causes harsh or soft shifts.
- Servo seal/bore
- The servo piston seal and bore that apply a band; leakage causes band slip and a specific gear fault.
- Final fluid-level set
- Setting the exact ATF level at the specified temperature after a road test, since level changes as the unit warms and fills.