Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSCHEVROLET1987FORWARD CONTROL 4.8 T, AUTOMATIC, 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)TRANSMISSIONAUTOMATIC TRANSDIAGNOSIS - TORQUE CONVERTER CLUTCH - TRUCKSTROUBLE SHOOTINGTURBO HYDRA-MATIC 400
1987 Chevrolet Forward Control 4.8 T, Automatic, 400/M40
Turbo Hydra-MATIC 400
1987 Chevrolet Forward Control 4.8 T, Automatic, 400/M40SECTION Turbo Hydra-MATIC 400
Every diagnosis of automatic transmission problems should begin with a check of the transmission fluid and linkage. Most of the following conditions can be caused by one or more of the following factors:
- Incorrect fluid level
- Contaminated fluid
- Improperly adjusted linkage
- Damaged or worn linkage.
TURBO HYDRA-MATIC 400 TROUBLE SHOOTING
| Condition | Possible Cause | Correction |
|---|---|---|
| No or Delayed 1-2 Shift | ||
| Improper fluid level | Check fluid level; See GENERAL SERVICING | |
| No or Delayed 1-2 Shift - Disconnect Electrical Plug From Transmission | ||
| Normal upshift | Check for short circuit and correct detent switch or wiring | |
| No upshift | Perform LINE PRESSURE test; Service as required | |
| 1-2 Shift Complaints | ||
| Improper fluid level | Check fluid level; See GENERAL SERVICING | |
| Poor engine performance | Check and tune engine | |
| Improper line pressure | Perform LINE PRESSURE test; Service as required | |
| Vacuum system leaking | Check vacuum lines and modulator; Service as required | |
| 2-3 Shift Complaints | ||
| Improper fluid level | Check fluid level; See GENERAL SERVICING | |
| Poor engine performance | Check and tune engine | |
| Drives In Neutral (Creeps) | ||
| Manual linkage binding or out of adjustment | Adjust or service linkage; See GENERAL SERVICING | |
| Manual valve dis- connected or end broken | Service as required | |
| Pressure leak into forward clutch apply passage | Check pump assembly and service as required | |
| Wrong forward clutch plate usage or burnt plates | Determine cause of condition; Service as required | |
| Will Not Hold or Release Park | ||
| Manual linkage binding or out of adjustment | Adjust or service linkage; See GENERAL SERVICING | |
| Internal linkage damaged, mispositioned, or misassembled | Check and replace internal linkage components as required | |
| No Engine Braking in "L1" | ||
| Low-Reverse check ball mispositioned or missing, or case damaged at Low- Reverse check ball area | Replace check ball or case | |
| Rear servo oil seal ring, bore or piston damaged | Service as required | |
| Rear Servo band apply pin too short or improperly assembled | Service as required | |
| Rear band broken, burnt, not engaged on anchor pins and/ or servo pin | Determine cause of condition; Service as required | |
| No Engine Braking in "L2" | ||
| Front servo and accumulator oil rings and/or bores leaking, or front servo piston cocked or stuck | Service as required | |
| Front band broken, burnt, not engaged on anchor pin and/or servo pin | Service as required | |
| No or Slips in "R" | ||
| Improper fluid level | Check fluid level; See GENERAL SERVICING | |
| Manual linkage binding or out of adjustment | Adjust or service linkage; See GENERAL SERVICING | |
| Low Line Pressure (in "R") | Determine cause of condition; Service as required | |
| Normal Line Pressure (in "R") 2-3 valve train stuck open (also cause 1-3 shift in "D") | Clean and free valve; Service as required | |
| Cross channel leak or porosity in reverse feed passage in case or valve body | Determine cause and service as required | |
| Valve body gaskets leaking | Replace gaskets | |
| Rear servo piston seal ring damaged or missing | Replace servo piston seal ring | |
| Short rear servo band apply pin | Replace rear servo band apply pin | |
| Damaged rear servo piston or bore | Service as required | |
| Forward clutch does not release (also cause drive in "N") | Determine cause of condition; Service as required | |
| Direct clutch plate burnt | Determine cause of condition; Service as required | |
| Rear band broken, burnt, or apply pin or anchor pins not engaged | Determine cause of condition; Service as required | |
| Center support oil seal rings or grooves damaged or worn | Replace center support oil seal rings | |
| 1st & 2nd Only (No 2-3 Upshift) | ||
| Valve body gasket mispositioned or leaking, or 2-3 valve stuck | Service as required | |
| Direct clutch plates burnt | Determine cause of condition; Service as required | |
| Improper vacuum | Check engine vacuum lines and modulator; Service as required | |
| No Drive in "D" | ||
| Improper fluid level | Check fluid level; See GENERAL SERVICING | |
| Manual linkage binding or out of adjustment | Adjust or service linkage; See GENERAL SERVICING | |
| Low Line Pressure (in "D") | Determine cause of condition: Service as required | |
| No Drive in "D" - Normal Line Pressure (in "D") | ||
| Forward clutch feed passage not drilled or restricted in pump assembly | Service as required | |
| Forward clutch plates burnt | Determine cause of condition: Service as required | |
| Low roller clutch damaged or installed backward | Service as required | |
| NO DETENT DOWNSHIFT - Place Vehicle on lift. Turn ignition on (engine off). Unplug electrical plug from trans- mission. Connect test light to "detent" terminal of disconnected wiring harness. Fully depress accelerator. - LIGHT ON | ||
| Detent solenoid in- operative, poor con- nections, shorted wire, open wire, valve stuck, or orifice plugged | Service as required | |
| Detent valve train stuck or binding in valve body | Clean and free valve; Service as required | |
| NO DETENT DOWNSHIFT - Place Vehicle on lift. Turn ignition on (engine off). Unplug electrical plug from trans- mission. Connect test light to "detent" terminal of disconnected wiring harness. Fully depress accelerator. - LIGHT OFF | ||
| Detent solenoid switch inproperly adjusted | Adjust detent solenoid switch; See GENERAL SERVICING | |
| Faulty switch, con- nections, fuse, or shorted wire | Service as required | |
| TRANSMISSION NOISY Park, Neutral & All Driving Ranges | ||
| Improper fluid level | Check fluid level; See GENERAL SERVICING | |
| Wrong, plugged, or restricted oil filter | Replace oil filter | |
| Pump intake pipe split, "O" ring damaged, or porosity in case intake pipe hose | Service as required | |
| Water in fluid | Determine cause of condition; service as required and replace fluid | |
| Porosity or voids at transmission case (pump face) intake port | Service as required | |
| Pump-to-case gasket mispositioned | Replace gasket | |
| Pump gears damaged, faulty, driving gear installed backward; cresent inter- ference; pressure regulator cup plug damaged or missing; seal rings damaged or worn | Service as required | |
| Loose converter-to- flywheel bolts | Tighten bolts and check for damage; Service as required | |
| TRANSMISSION NOISY 1st, 3rd & "R" Only | ||
| Planetary gears or thrust bearings damaged | Thoroughly clean bearings and races; Inspect needle bearings and surfaces for pitting and roughness; Replace planetary gear set | |
| Planetary gear set front internal gear ring damaged | Replace planetary gear set | |
| TRANSMISSION NOISY During Accel in Any Gear | ||
| Transmission cooling lines grounded to underbody | Service as required | |
| Broken or loose motor mounts | Replace motor mounts | |
| TRANSMISSION NOISY Squeak at Low Speeds | ||
| Speedometer driven gear shaft seal faulty or needs lubrication | Service as required | |
| Extension housing oil seal faulty or needs lubrication | Service as required | |
RENDER: 1.0x
NO RELATED
Recommended Tools & Savings
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.