Overhaul - Thm 400 GMC Pickup R1500

APPLICATION

TRANSMISSION APPLICATION (CADILLAC)

TRANSMISSION APPLICATION (CHEVROLET)

TRANSMISSION APPLICATION (GMC)

IDENTIFICATION

Transmission serial number is located on identification plate attached to right side of transmission case. (Scheme 54) Number consists of model year, 2 letter model code, and production serial number.

Scheme 54

DESCRIPTION

Transmission consists of a 3-element torque converter and compound planetary gear set. Three multiple disc clutches, 2 roller clutches, and 2 bands provide friction elements necessary to control functions of planetary gear set.

LUBRICATION & ADJUSTMENTS

See appropriate SERVICING - A/T article.

SERVICE (IN VEHICLE)

The following components can be removed with transmission in vehicle

1. Governor Cover and Seals.
2. Governor Assembly.
3. Governor Pipes.
4. Intermediate Servo Piston Assembly.
5. Rear Servo Assembly.
6. Front Servo Assembly.
7. Oil Pan and Oil Screen (Intake Pipe) Assembly.
8. Valve Body Assembly.
9. Check Balls and Valve Body Spacer Plates and Gaskets.
10. Pressure Regulator Parts.
11. Manual Detent Roller and Spring Assembly.
12. Parking Pawl Actuator Rod.
13. Parking Pawl Bracket and Parking Pawl.
14. Manual Shaft and Seal.
15. Manual Valve and Valve Link.
16. Extension Housing and Gasket.
17. Rear Seal.
18. 1-2 Accumulator Assembly.
19. Vacuum Modulator.
20. Oil Filter Pipe and "O" Ring.
21. Speedometer Driven Gear Assembly.
22. Cooler Fittings.
23. Downshift Solenoid.
24. Electrical Connectors.
25. Governor Feed Screen.
26. Pump Pressure Screen.
27. Modulator Valve.

ROAD TEST

1. Connect tachometer to engine. Place selector lever in "Drive" range and accelerate vehicle from standstill at minimum throttle opening.
2. The 1-2 and 2-3 upshifts should occur as vehicle reaches correct speed. As vehicle speed decreases, 3-2 and 2-1 downshifts and engine braking effect should be noticed. See «SHIFT POINT SPECIFICATIONS»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400) . SHIFT POINT SPECIFICATIONS Application Speed (MPH) Upshift Minimum 1-2 15 2-3 30 Detent Downshift Minimum 3-2 68-73 2-1 28-32 Upshift Maximum 1-2 44-48 2-3 77-83
3. Stop vehicle and place selector lever in "2" (Intermediate) range. Accelerate from standstill. Upshift 1-2 should occur at all throttle openings (shift point will vary with throttle opening). The 2-3 upshift should occur. Stop vehicle and place selector lever in "1" (Low) range. Accelerate from standstill. No upshift should occur.
4. With selector lever in Drive range and vehicle speed at 35 MPH, move selector lever to "2" (Intermediate) range. Transmission should downshift to 2nd gear. Increase in engine RPM and engine braking effect should be noticed.
5. With selector lever in "2" (Intermediate) range and vehicle speed at 25-35 MPH (not over 40 MPH), move selector lever to "1" (Low) range. Throttle must be in closed position. Transmission should downshift to 1st gear. Increase in engine RPM and engine braking effect should be noticed. Stop vehicle and place selector lever in Reverse. Check for reverse operation.

CLUTCH & BAND APPLICATIONS

Scheme 55

Scheme 56

1. Install 0-300 psi (0-21 kg/cm 2 ) Pressure Gauge (J-5907) at pressure take-off point at left side of transmission to rear manual lever. (Scheme 55) Place gauge where it can be seen from driver's seat. Connect tachometer to engine.
2. Hydraulic pressures can be checked with transmission fluid at correct level and operating temperature. Check pressures with vehicle stationary and brakes applied. See «HYDRAULIC PRESSURES»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400). CAUTION: For control pressure tests, total running time in Drive and Reverse ranges with brake applied must not exceed 2 minutes. Damage to transmission may result. HYDRAULIC PRESSURES Range @ RPM psi (kg/cm 2 ) Neutral (1) @ 1000 55-70 (4-5) Drive @ Idle 60-85 (4.2-6) Drive (1) @ 1000 60-90 (4.2-6.3) Low or "2" (1) @1000 135-160 (9.5-11.2) Reverse (1) @1000 95-150 (6.7-10.5) Drive (1) (2) @1000 90-110 (6.3-7.7) (1) Brakes applied. (2) Downshift switch activated.
3. On vehicles equipped with Exhaust Gas Recirculation (EGR), throttle is open enough in Drive range at 1000 RPM to cause EGR valve to open. This allows exhaust gas to enter intake manifold and lower manifold vacuum. Transmission line pressure rises with lower intake manifold vacuum. Line pressure may go above upper limit.
4. If high line pressures are obtained, disconnect and plug vacuum line at EGR valve. Recheck line pressure. If high pressures are still found, check engine vacuum. If low intake vacuum is found, use hand operated vacuum pump and apply 20 in. Hg vacuum to modulator.
5. Recheck pressures according to table. If line pressures are normal with external vacuum applied, check engine vacuum and vacuum systems for leaks. If high line pressures are found, refer to «CONTROL PRESSURE RESULTS»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400) for possible causes.
6. When stationary testing is complete, drive vehicle at 30 MPH and allow throttle to close completely. Read pressure on gauge. This test may also be conducted on hoist. Run engine at 3000 RPM with driving wheels off ground, selector in Drive, and brakes released. Close throttle and read pressure between 2000 and 1200 RPM. Pressure should read 55-70 psi (3.8-4.9 kg/cm 2 ).

Line Pressure Too Low

1. Transmission fluid level low, faulty vacuum modulator assembly. Filter blocked or restricted, "O" ring on filter intake pipe omitted or damaged, intake pipe split or leaking, or incorrect filter.
2. Pump assembly damaged, worn, or mismatched parts. Pump gear clearance damaged or worn. Pressure regulator spring too weak or not enough spacers in pressure regulator.
3. Internal leak in direct clutch circuit (pressure normal in Neutral, Low, Intermediate and Drive, but low in Reverse). Internal leak in forward clutch circuit (pressure normal in Neutral and Reverse, low in Drive).
4. Case assembly porous in intake bore area. Missing plug or leak at intermediate clutch plug. Low-Reverse check ball installed wrong or missing (causing loss of Reverse and no engine braking in low).

Line Pressure Too High

1. Vacuum system leak or improper engine vacuum. Water in vacuum modulator. Modulator valve not operating properly or defective. Defective EGR valve.
2. Detent switch actuated or shorted, detent solenoid stuck open. Detent feed orifice in spacer plate blocked, detent solenoid loose. Detent valve bore plug damaged. Detent regulator valve pin too short.
3. Pump pressure regulator and/or boost valve stuck. Incorrect pump pressure regulator spring. Pressure boost valve installed backward. Too many pressure regulator valve spacers. Pump casting defective. Aluminum bore plug has hole or not working. Pressure boost bushing broken or not working.
4. Control valve assembly-to-spacer gasket out of proportion, control valve assembly gaskets switched.

GOVERNOR CHECK

1. Raise vehicle on hoist (rear wheels off ground). Disconnect and plug vacuum line to modulator. Connect pressure gauge to transmission and tachometer to engine.
2. Start engine, keep foot off brake pedal, move selector lever to Drive range, and check line pressure at 1000 RPM. Slowly increase engine speed to 3000 RPM and determine if line pressure drop of 10 psi (.7 kg/cm 2 ) or more occurs.
3. If no pressure drop occurs, inspect governor for stuck valve or weight, or restricted orifice in valve. Ensure governor valve entry and exhaust has .020" (.51 mm) minimum opening.
4. Check governor feed system. Check control valve assembly or case screen. Check governor pipe for restrictions and proper fit in case holes. Control valve assembly should be disassembled, cleaned, and inspected if pressure drop of 10 psi (.7 kg/cm 2 ) or more occurs (with transmission malfunction).

Vacuum Diaphragm Leak Check

Insert pipe cleaner into vacuum connector pipe as far as possible and check for transmission fluid. If fluid is found, replace modulator. Gasoline or water vapor may settle in vacuum side of modulator. If this is found without presence of fluid, modulator should not be changed. If vehicle is to be exposed to temperatures 10°F or below, modulator MUST be replaced.

Atmospheric Leak Check

Apply soap bubble solution to vacuum connector pipe seam (crimped upper-to-lower housing seam). Use a hose and blow air pressure into vacuum pipe and check for leaks. If leaks are present, replace modulator.

Bellows Comparison Check

1. Using Comparison Gauge (J-24466), compare load of vacuum modulator with known good modulator of same type. Part number is stamped on modulator dome. Install good modulator on either end of gauge.
2. Install modulator in question on opposite end of gauge. Holding modulators in horizontal position, bring them slowly together under pressure. If modulator in question is bad, gauge line will remain Blue. If modulator in question is good, gauge line will be White.

Sleeve Alignment Check

Roll main body of modulator on flat surface and observe sleeve for concentricity to can. If sleeve is concentric and plunger is free, modulator is okay.

VACUUM REGULATOR VALVE (DIESEL MODELS ONLY)

1. Attach vacuum regulator valve to fuel injection pump. Valve body must be securely attached but free to rotate on pump. Attach vacuum source of 9.0-10.4 psi (.6-.7 kg/cm 2 ) to bottom vacuum nipple. Attach vacuum gauge to upper nipple.
2. Insert vacuum regulator gauge bar between gauge boss on injection pump and wide open stop screw on throttle lever. Rotate throttle shaft and hold lever against gauge bar. Slowly rotate vacuum regulator valve body clockwise.
3. Setting will only be valid if performed with clockwise rotation. When vacuum gauge reads 5.3-5.9 psi (.37-.41 kg/cm 2 ), tighten valve body mounting screws. Check setting by releasing throttle lever to idle stop position.
4. Rotate throttle shaft back until lever rests against gauge bar again. Check vacuum gauge reading and ensure it is still 5.3-5.9 psi (.37-.41 kg/cm 2 ). If not to specification, reset valve and check setting again.

DOWNSHIFT SOLENOID CHECK

1. Place selector lever in "Park". Turn ignition switch "ON", but do not start engine. From under hood, slowly move throttle linkage to wide open position. One click should be heard from transmission.
2. Allow throttle to return to closed position. One click should be heard from transmission. If clicks are heard, downshift solenoid is operating properly. If solenoid does not operate as outlined, go to step 3).
3. Use test light to check Brown wire at connector on side of transmission case. Test light should light with throttle wide open and go out when throttle is released.
4. If test light operates as described, but solenoid did not click during tests, replace solenoid after first check to ensure internal wiring is operational.
5. If test light fails to light with throttle open, solenoid circuit is open. If light lights with throttle closed, solenoid circuit is shorted. Check transmission control fuse in fuse panel. Check solenoid circuit and repair open or short (Orange wire with Black stripe).

REMOVAL & INSTALLATION

See appropriate REMOVAL & INSTALLATION - A/T article.

END PLAY CHECK

Install Torque Converter End Play Checker (J-21371). (Scheme 57) Converter end clearance should be less than.024" (.60 mm). If clearance is greater than specification, replace torque converter assembly.

Scheme 57

VACUUM MODULATOR & VALVE

Disconnect vacuum hose from modulator stem. Remove vacuum modulator attaching screw and retainer. Remove modulator and "O" ring seal from case. Discard "O" ring. Using magnet, remove modulator valve from case bore.

GOVERNOR

Remove attaching screws, cover, and governor assembly. On internal speed sensor equipped transmissions, remove retaining bolt, speed sensor and "O" ring, being careful not to distort cover. Remove governor assembly by pulling straight out of case.

SPEEDOMETER DRIVEN GEAR

Disconnect speedometer cable. Remove attaching screw and retainer. Remove speedometer driven gear assembly and "O" ring from case.

INTAKE PIPE, FILTER & PAN

Remove pan attaching bolts and pan. Remove filter retaining bolt. Withdraw intake pipe and filter assembly. Discard filter and "O" ring seal from intake pipe. (Scheme 58)

Scheme 58

CONTROL VALVE ASSEMBLY

Remove control valve attaching bolts, manual detent spring and roller. Note size and location of each bolt for reassembly reference. Remove governor oil pipes from case and rotate away from holes. Remove governor oil screen from inboard hole. Remove control valve assembly.

SOLENOID

Remove wire connecting solenoid to exterior electrical connector. Remove solenoid attaching screws and solenoid. Use care to not press against solenoid cover. Remove valve body to spacer plate gasket, spacer plate and spacer plate to case gasket. Using magnet, remove 6 check balls.

FRONT & REAR SERVO ASSEMBLY

Remove servo piston assembly, retainer and spring. Remove bolts, cover, gasket, rear servo piston and seal. Perform band apply pin selection check at this time to determine correct pin for use at reassembly. This is equivalent to band adjustment.

Scheme 59

1. Position Band Apply Pin Selection Gauge (J-21370-6) on transmission case over rear servo bore. (Scheme 59) Hex nut on side of gauge faces toward parking brake linkage. End of Gauge Pin (J-21370-5) with smaller diameter fits in servo pin bore.
2. Secure gauge with 2 attaching screws. Tighten screws to 18 ft. lbs. (24 N.m). Ensure stepped gauge pin is free to move in both tool and servo pin bore. Stepped side of pin must face front of transmission case.
3. Apply 25 ft. lbs. (34 N.m) of force to hex nut on side of gauge. This will cause lever on top of gauge to depress stepped gauge pin into servo pin bore, simulating actual operating conditions. Note relation of steps on gauge pin and machined surface on top of gauge. If gauge pin is even with top of gauge surface or above upper step of pin, use long pin. If gauge pin is between upper and lower steps, use medium pin. If gauge surface is even with or below step on gauge pin, use short pin.
4. If new band apply pin is required, make note of pin size for reassembly reference. Remove selection gauge from transmission case.

FRONT UNIT END PLAY CHECK

1. With transmission removed, remove one oil pump attaching bolt and washer at 10 o'clock position. Install Slide Hammer Bolt (J-6125) into bolt hole. Mount Dial Indicator (J-8001) on bolt.
2. Press turbine shaft to rear and output shaft forward to eliminate slack. Set indicator tip to register with end of turbine shaft. Zero dial indicator. Pull out on turbine shaft and note measurement. End play should be .003-.024" (.08-.61 mm).
3. If end play is not within specification, select correct thrust washer for use at reassembly. Thrust washer controlling end play is located between pump cover and forward clutch housing. See «FRONT UNIT THRUST WASHERS»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400) .

FRONT UNIT THRUST WASHERS

REAR OIL SEAL & EXTENSION HOUSING

If replacement is necessary, pry rear oil seal from extension housing. Remove attaching bolts and remove extension housing and gasket from transmission.

Note. Check front unit end play before proceeding with transmission disassembly. Record end play for reassembly procedure.

OIL PUMP

If front seal requires replacement, pry seal out before removing pump assembly. Remove pump attaching bolts and install Oil Pump Remover (J-24773-1). Remove oil pump assembly, pump seal and gasket. (Scheme 60)

Scheme 60

DETENT LEVER, MANUAL LEVER, SHAFT & PARKING LINKAGE

1. Remove manual linkage. Loosen lock nut holding inside detent lever to manual shaft. Remove manual shaft-to-case pin. Remove lock nut and inside detent lever from manual shaft. Remove manual shaft. (Scheme 61)
2. Remove parking actuator rod and detent lever. Remove attaching bolts and parking lock bracket. Remove parking pawl return spring. Remove parking pawl shaft spring retainer. Remove parking pawl shaft cup plug. Pry outward to remove plug. Remove parking pawl shaft and parking pawl.

Scheme 61

TURBINE SHAFT, FORWARD, INTERMEDIATE & DIRECT CLUTCH ASSEMBLIES, SUN GEAR SHAFT & FRONT BAND

Remove forward clutch and turbine shaft assembly from case. Remove forward clutch hub-to-direct clutch housing thrust washer. Remove direct clutch and intermediate roller assembly. Remove sun gear shaft. Remove front band assembly.

REAR UNIT END PLAY CHECK

1. Transmission must be out of vehicle and extension housing must be removed. Install Speedometer Puller Bolt (J-21797) in an extension housing bolt hole. Install dial indicator.
2. Zero dial indicator, move output shaft in and out, and note end play. (Scheme 62) End play should be.007-.019" (.18-.48 mm). If not within specification, change thrust washer.
3. Thrust washer controlling rear unit end play has 3 tabs. It is located between output shaft thrust washer and rear face of transmission case. Notches and/or numerals on tabs of washer identify thickness. See «REAR UNIT THRUST WASHERS»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400).

Scheme 62

REAR UNIT THRUST WASHERS

Scheme 63

1. Remove center support bolt from valve body using a 3/8", 12-point thin wall deep socket. (Scheme 63) Remove intermediate clutch backing plate-to-case snap ring. Withdraw backing plate and 6 clutch plates (3 composition and 3 steel).
2. Remove center support-to-case snap ring. Install Remover (J-21795) on end of mainshaft so tangs engage groove in shaft. Tighten screw on tool to secure tool on shaft. This will prevent roller clutch movement during gear unit removal. NOTE: Install piece of pipe over output shaft for use as handle and to prevent spline damage to case bushing when removing gear unit, center support and reaction carrier.
3. Loosen transmission holding fixture pivot pin slightly so gear unit assembly will not bind during removal from case. With transmission case in horizontal position, shift complete assembly forward and remove from case.
4. Remove output shaft-to-case thrust washer from shaft or case. Place gear unit assembly in Holding Fixture (J-6116 01) using Adapter (J-21364) with mainshaft pointing up. Remove rear unit selective washer from transmission case. Remove center support-to-case spacer.
5. Rotate rear band lugs away from pins and pull band assembly from case. Lifting straight up, remove center support assembly from reaction carrier. Remove center support-to-reaction carrier thrust washer.
6. Washer may be stuck to back of center support. Remove reaction carrier and roller clutch assembly from output carrier. Remove roller clutch assembly from reaction carrier.

COMPONENT DISASSEMBLY & REASSEMBLY

Note. When reassembling transmission, lubricate all bushings, seals, thrust bearings, and mating surfaces with transmission fluid. Use petroleum jelly to lubricate and retain thrust washers. Use compressed air to dry parts. NEVER use rags to dry parts.

Scheme 64

Scheme 65

Scheme 66

Scheme 67

Scheme 68

1. Governor, except driven gear, is serviced as a complete assembly. Driven gear may be serviced separately and requires disassembly of governor for gear replacement.
2. Governor weights are interchangeable from side to side. Cut off one end of each governor weight pin and remove pins, governor thrust cap, governor weights and springs. Remove governor valve from governor sleeve. (Scheme 64)

Inspection

1. Wash all parts in solvent and air dry. Blow out all passages. Inspect sleeve for wear or damage. Check for free operation in case bore. Check driven gear for looseness on sleeve.
2. Ensure valve opening at entry and exhaust is .020" (.51 mm) minimum. Valve opening measurements are made with driven gear up and thrust cap down. Entry measurement is made with weights extended while exhaust is measured with weights inward.

Driven Gear Replacement

1. Drive out gear retaining split pin. Support assembly on 3/16" plates installed in exhaust slots of sleeve. Using a press, press gear out of sleeve with long punch. Clean governor sleeve of chips.
2. To install new gear, press gear into sleeve until nearly seated. Remove any chips that may have been shaved off gear. Press gear in until bottomed on shoulder.
3. New pin hole must be drilled through sleeve and gear. Support governor in press. Locate hole position 90 degrees from existing hole. Center punch and drill new hole through sleeve and gear with 1/8" drill bit. Install new pin.

Reassembly

Install valve in bore of sleeve, then install weights, springs, and thrust cap on sleeve. Align pin holes in thrust cap, weight assemblies, and sleeve. Install new pins. Crimp both ends of pin to prevent them from falling out. Check weight assemblies for free operation in sleeve. Ensure valve is free in sleeve.

Note. As each valve is removed, place parts in order for reassembly reference. Valves and springs are not interchangeable. All components must be laid out on a clean surface in exact sequence as they were removed

Disassembly

1. Position control valve assembly with gasket surface up and accumulator pocket at bottom. Remove manual valve from upper bore. Install Compressor (J-21885) on accumulator piston. Compress piston and remove "E" retaining ring. Remove piston and spring.
2. Remove retaining pins (except grooved pin in lower left bore) from bores with pin punch. Drive pins from outer side of valve body. When removing pins, hold hand over bore end in case spring forces components out of bore. (Scheme 69)and (Scheme 70). Remove grooved pin from lower left bore with long nose pliers. Remove valve trains beginning with upper left corner.

Scheme 69

Scheme 70

Clean and inspect all parts. If burrs are present on valves, remove with a fine stone. Use care not to round off shoulders of valves. Ensure valves slide freely by their own weight.

Note. DO NOT remove Teflon oil seal from front accumulator piston unless seal ring needs replacing. Service oil seal ring is cast iron.

Install front accumulator spring and piston into valve body. Compress piston and spring and install retaining "E" clip. To install remaining components, reverse disassembly procedure.

Remove rear accumulator piston from rear servo piston. Remove rear servo piston-to-band apply pin "E" clip. Remove seal and rear servo piston from pin. Remove washer, spring and spring retainer.

Check oil seal rings. Inspect fit of band apply pin in servo piston. Inspect band apply pin for scores or cracks. Ensure band apply pin is proper size as selected during disassembly. See Band Apply Pin Selection Check in TRANSMISSION DISASSEMBLY .

To reassemble rear servo components, reverse disassembly procedure.

Inspect servo pin, piston and oil seal ring for wear or damage. Check fit of servo pin in piston and in case bore. (Scheme 71)

Scheme 71

1. Compress regulator boost valve bushing against pressure regulator spring. Carefully remove snap ring. CAUTION: Pressure regulator spring is very tightly compressed.
2. Remove regulator boost valve bushing, valve and pressure regulator spring. Remove regulator valve, spring retainer, and spacer(s) (if present). Remove 5 pump cover attaching bolts noting different lengths and positions. Separate cover from body. Mark drive and driven gears for reassembly reference and remove from pump body. (Scheme 60)
3. Reassembly of pump gears in same position will ensure quietest operation. Remove retaining pin and bore plug from end of regulator bore. Remove 2 oil seal rings from cover. Remove pump-to-forward clutch housing thrust washer.

Inspect all parts for wear or damage. Check pump body face-to-gear face clearance with feeler gauge and straightedge. Clearance should be .0008-.0035" (.020-.089 mm). Ensure 1/8" breather hole in pump cover is open.

1. When installing front unit thrust washer, ensure it is proper thickness as determined at disassembly. See FRONT UNIT END PLAY CHECK in «TRANSMISSION DISASSEMBLY»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400) . To reassemble remaining components, reverse disassembly procedure. Leave pump cover bolts one turn loose.
2. Install Alignment Band (J-21368) to align cover and body. Tighten attaching bolts and remove alignment band. Install new square-cut "O" ring on pump. Install new pump oil seal on front of pump using Oil Seal Installer (J-21359).

Bushing Replacement

1. To replace oil pump body bushing, drive bushing from body with Remover/Installer (J-8092 and J-21465-17). Clean pump bushing bore. Drive bushing squarely into bore until flush or .010" (.25 mm) below gear pocket face.
2. To replace stator shaft rear bushing, mount pump cover in vise with stator shaft held in brass jaws. Assemble Remover (J-21465-15) to slide hammer and Adapter (J-2619 and J-2619-4) and remove bushing.
3. Clean shavings from stator bore. Place pump cover in vise with stator shaft resting on block of wood. Place new bushing on shoulder of Installer (J-21465-2). Bushing should be driven to depth of 19/32".
4. To replace stator shaft front bushing, mount pump cover in vise with stator shaft held in brass jaws. Attach Bushing Remover (J-21465-15) to slide hammer and Adapter (J-2619 and J-2619-4) and remove bushing.
5. Clean shavings from stator shaft. Assemble installer with Drive Handle (J-21465-3 and J-8092). Support hub of pump cover on soft material to protect ring lands and install bushing.

Scheme 72

Scheme 73

1. Place forward clutch assembly in Adapter and Holding Fixture (J-21364 and J-6116-01) with turbine shaft pointing down. Remove forward clutch housing-to-direct clutch hub snap ring and withdraw hub. Remove forward clutch hub and one thrust washer from each side of hub. (Scheme 73)
2. Remove composition and steel clutch plates. Place forward clutch assembly in press with turbine shaft pointing down. Using Clutch Spring Compressor and Adapter (J-4670-01 and J-21664), compress spring retainer and remove snap ring. Remove tools. Lift out spring retainer and 16 clutch release springs. NOTE: Keep forward clutch release springs separate from direct clutch release springs.
3. Remove forward clutch piston from housing. Remove inner and outer seals. Remove center piston seal from clutch housing. If turbine shaft or housing is damaged, place housing in press with shaft facing down. Using 3" driver, press turbine shaft out of forward clutch housing.

Inspect all components for wear or excessive damage. Ensure lubrication passages in housing, hub, and turbine shaft are clear. Check piston for cracks. Check turbine shaft and clutch housing for wear, scoring, or other damage. Ensure check ball in housing moves freely.

1. If turbine shaft was removed, place forward clutch housing in press with flat side up. Align shorter splined end of turbine shaft with splines in forward clutch housing. Carefully press shaft into housing until shaft bottoms out. NOTE: Start shaft into housing, then back off press so shaft can straighten itself. Repeat until shaft is going in straight.
2. Invert forward clutch housing on press with turbine shaft pointing down. Oil and install inner and outer seals on clutch piston with seal lips facing away from spring pockets. Oil and install center seal in clutch housing with seal lips facing upward.
3. Place Inner Seal Protector (J-21362) over clutch hub. Place clutch piston into Installer (J-21409). Install assembly into housing, rotating piston clockwise slightly until seated. Install 16 clutch release springs into piston pockets. (Scheme 72)
4. Place spring retainer over springs and compress springs with Compressor and Adapter (J-4670-01 and J-21664). Use care to avoid catching retainer in snap ring groove. Install snap ring. Remove tools and ensure all release springs are straight.
5. Install forward clutch hub thrust washers. Ensure bronze washer is installed on side of hub facing forward clutch housing. Place forward clutch hub in clutch housing.
6. Lubricate clutch plates with transmission fluid. Install clutch plates, starting with waved steel plate, then alternating composition and flat steel plates until all clutch plates are installed. (Scheme 75)
7. Install direct clutch hub and retaining snap ring. Place forward clutch housing on oil pump delivery sleeve. Check operation of forward clutch by applying air through forward clutch passage. (Scheme 74)

Scheme 74

Scheme 75

1. Remove roller retainer snap ring and clutch retainer. Remove roller outer race and roller assembly. Turn unit over and remove direct clutch backing plate-to-clutch housing snap ring. Remove direct clutch backing plate and clutch pack.
2. Compress spring retainer and remove snap ring. Use either Clutch Spring Compressor (J-4670), Rear Clutch Spring Compressor (J-6129), or press and Adapter (J-21664) to compress spring retainer. Remove retainer and 14 clutch release springs. NOTE: Keep direct clutch release springs separate from forward clutch release springs.
3. Remove direct clutch piston from clutch housing. Remove inner and outer seals from piston. Remove center piston seal from direct clutch housing.

Scheme 76

Scheme 77

Scheme 78

Check all parts for excessive wear or damage. Ensure oil passages are open. Ensure free operation of check ball in clutch housing. Check release springs for collapsed coils and distortion.

Scheme 79

1. Install apply ring onto piston. (Scheme 76) Install waved clutch plate or dished clutch plate into direct clutch housing. Install clutch plates. Alternate steel and composition plates. (Scheme 77) Install direct clutch backing plate and snap ring.
2. Install roller assembly or sprag assembly. Install intermediate clutch race with clockwise motion. When install properly it should not rotate counterclockwise. Install intermediate clutch retainer and snap ring.
3. Check operation of clutch with air. (Scheme 79) Apply air through left oil feed hole. Air applied through right oil feed hole (reverse passage) should escape through left oil feed hole.

Remove 4 center support oil seal rings. Compress spring retainer and remove snap ring. Remove spring retainer and 3 clutch release springs. Remove intermediate clutch spring guide and clutch piston from center support. Remove inner and outer piston seals.

Use Driver (J-21465-6) to remove bushing. To install new bushing, align slot in bushing with drilled hole in oil delivery sleeve closest to piston. Drive bushing into bore no more than .010" (.25 mm) below top of delivery sleeve.

Check all parts for excessive wear or damage. Ensure all passages, lubrication grooves and holes are clear of obstructions. Ensure constant bleed orifice is open .020" (.51 mm).

1. Install waved plate (if used). Install steel plates and composition plates alternately. (Scheme 80) Install intermediate clutch backing plate and snap ring. Lubricate and install inner and outer seals on piston with seal lips facing away from spring pockets. Place Seal Protector (J-21363) over center support hub. Install intermediate clutch piston. Ensure piston fully seats in center support.
2. Install plastic spring guide and evenly space 3 release springs in holes of spring guide. Place spring retainer over springs. Compress springs and install snap ring in groove. Install 4 oil seal rings on center support. To check clutch piston, apply air to center oil feed hole.

Scheme 80

1. Remove thrust bearing, races and reaction carrier. Remove sun gear, thrust washer and front internal gear ring. Remove snap ring, output shaft and "O" ring.
2. Remove thrust bearing and races from rear internal gear. Remove rear internal gear and mainshaft. Remove snap ring from mainshaft. Remove races and bearings.

1. Check all components for excessive wear or damage. Ensure lubrication holes are open. Check teeth and bearing surfaces. Inspect splines and gears.
2. Pinion end play range is .009-.024" (.23-.61 mm). Check roller clutch assembly for damage to rollers, springs, or clutch cage. Inspect sun gear and sun gear shaft for damage or wear to splines, teeth, and bushings.

Speedometer Drive Gear/Speed Sensor Rotor Replacement

Use Puller and Gear Remover (J-8433 and J-21427-01) to remove speedometer drive gear or rotor. To install rotor, use Rotor Installer (J-36352-3) or Rotor Installer Mechanical Press (J-36352-5). To install speedometer drive gear and clip, use Speedometer Gear Installer (J-5590).

Output Shaft Bushing Replacement

To remove, use Bushing Remover (J-21465-16). To install bushing use Driver (J-21465-1). Bushing must be installed so oil hole in flange is aligned with oil hole in hub. Notch in bushing must face outward.

Sun Gear Shaft Bushing Replacement

To remove, use Bushing Remover (J-21465-15). To install, use Driver (J-21465-5) and drive into place until tool bottoms.

Pinion Gear Replacement

1. Support carrier assembly on front face. To avoid damage to carrier when removing pin, use a 1/2" drill bit and remove stake marks from end of pin. DO NOT remove any material from carrier as it will weaken and possibly crack.
2. Using a tapered punch, remove pinion pins from carrier. Remove pinion gears, thrust washers and roller needle bearings. Check pinion pocket thrust faces for burrs.
3. Install 18 needle bearings into each pinion. Use pinion pin as guide and petroleum jelly to hold bearings in place. Place a bronze and steel washer on each side of pinion so steel washer is against pinion.
4. Place pinion gear assembly in carrier. Install pilot shaft through rear face of assembly to hold parts in place. Drive in new pinion pin from front while rotating pinion gear.
5. Ensure headed end is flush or below face of carrier. Use punch held in bench vise for an anvil. Place carrier over punch and stake pinion pin in 3 places with blunt radius chisel.

Note. Both ends of pinion pin must lie below face of carrier or interference may occur.

Reassembly (Complete Gear Assembly)

1. Install thrust bearing-to-sun gear race, thrust bearing, and thrust bearing-to-rear internal gear race on grooved end of mainshaft. Install mainshaft into rear internal gear. Install thrust bearing-to-sun gear race, bearing, and thrust bearing-to-output shaft on mainshaft.
2. Install snap ring on mainshaft. Install mainshaft assembly to output shaft. Install snap ring and "O" ring seal. Install gear ring over output carrier. Install thrust washer into output carrier. Ensure tabs are in pockets. Lubricate pinion gears with transmission fluid and install reaction carrier into output carrier.
3. Install sun gear, chamfered inside diameter first, into reaction carrier assembly. Install sun gear shaft with long splined end first. Install thrust bearing-to-center support race on sun gear shaft. Ensure flange is up against sun gear. Install needle thrust bearing. Install thrust bearing-to-center support races.
4. Install thrust washer in recess of center support. Install reaction drum spacer and roller clutch assembly into reaction carrier. Install center support-to-reaction carrier thrust washer into recess in center support. Install center support into roller clutch in reaction carrier. NOTE: With reaction carrier held stationary, center support should rotate counterclockwise only.
5. Install Holding Tool (J-21795-02) so tangs engage groove in mainshaft. Tighten set screw to prevent movement of roller clutch during installation of gear unit assembly. Remove gear unit from holding tool. Place unit on side and install output shaft-to-case metal thrust washer (bent tabs in pockets).

Check for cracks, porosity, or interconnected passages. Check bores for scratches or scoring. Check band anchor pins for retention. Inspect intermediate clutch driven plate lugs and snap ring grooves for damage. Ensure parking pawl shaft cup plug is staked and sealed.

1. Position converter end of transmission case down and use Bushing Driver (J-21465-8) and soft-faced hammer to drive bushing out of case. Invert case to install new bushing. Use Drive Handle and Adapters (J-8092, J-21465-13, J-21465-8, and J-21465-9) to install new bushing.
2. Lubrication passage of bushing should face Adapter Ring (J-21465-9). Drive bushing into bore until adapter ring bottoms. Bushing should be .040-.055" (1.02-1.4 mm) above selective thrust washer surface. Stake bushing in place with Staker (J-21465-10). Staking marks must be in bushing groove.

Bushing should be 0-.010" (0-.25 mm) below oil seal counterbore surface. Stake bushing in place using Staker (J-21465-10). Stake marks must be in lube grooves.

PARKING PAWL

Install parking pawl with tooth toward center of transmission. Install parking pawl shaft and shaft retainer clip. Install new shaft cup plug using 3/8" diameter rod. Drive plug into case until shaft bottoms on case rib. Install parking pawl return spring with square end hooked on pawl. Install parking pawl bracket guides over parking pawl.

REAR BAND & GEAR UNIT

1. Install rear band assembly so 2 lugs index with 2 anchor pins. Ensure band is seated on lugs. Install previously selected rear unit end play washer into slots provided inside rear of case. See «REAR UNIT END PLAY CHECK»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400__rear-unit-end-play-check) . Place transmission case in horizontal position in holding tool.
2. Install complete gear unit assembly into case by lining up slots. Carefully guide assembly into case. Make sure center support bolt hole is aligned with hole in case.
3. Position transmission vertically with front end of case up. Install center support-to-case snap ring with beveled side up and flat side against center support. Locate gap adjacent to front band anchor pin. Expand snap ring until center support is against shoulder of case.
4. Install case-to-center support bolt. Carefully pry with punch to align bolt hole. Use care not to burr case valve body mounting surface. Lubricate intermediate clutch plates with transmission fluid. Start with waved steel plate. Alternate composition and flat steel plates until all clutch plates are installed.
5. Lubricate intermediate clutch plates with transmission fluid. Start with waved steel plate. Alternate composition and flat steel plates until all clutch plates are installed. Install intermediate clutch backing plate and snap ring.

FRONT BAND & CLUTCH ASSEMBLIES

Install direct clutch assembly onto intermediate clutch. Install front band. Install forward clutch on oil pump assembly. Check piston and clutch operation by applying air to forward clutch passage in pump. Install forward clutch with turbine shaft into transmission.

Scheme 81

1. Install gasket on transmission case. Install forward clutch and oil pump assembly in transmission case. Install oil pump-to-case bolts except bolt in 10 o'clock position to check end play. (Scheme 81) Tighten bolts to 18 ft. lbs. (24 N.m). CAUTION: If turbine shaft cannot be rotated as pump is being pulled into place, forward or direct clutch housings have been installed improperly and are not indexing with all clutch plates. This MUST be corrected before pulling pump fully into place.
2. Recheck front unit end play. See «FRONT UNIT END PLAY CHECK»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400__front-unit-end-play-check) under TRANSMISSION DISASSEMBLY. Install remaining pump attaching bolt with washer. Install front oil seal.

PARKING LINKAGE, DETENT LEVER & MANUAL SHAFT

Install new shaft seal. Install actuator rod into manual detent lever from side opposite pin. Install actuator rod plunger under parking bracket and over parking pawl. Install manual shaft through case and detent lever. Install lock nut on manual shaft and tighten. Install retaining pin, indexing with groove in manual shaft.

Note. If work is being performed with transmission installed, it may be necessary to bend manual shaft retaining pin. Straighten pin after installation.

EXTENSION HOUSING

Install extension housing with new gasket. Check "O" ring on output shaft. Install housing on transmission case and tighten bolts. Install rear oil seal.

Scheme 82

1. Install guide pins into control valve assembly attaching bolt holes. Install 6 check balls into ball seat pockets in case. If transmission is in vehicle, install check balls in pockets of spacer plate. (Scheme 82)
2. Install control valve spacer plate-to-case gasket. Install control valve spacer plate. Install detent solenoid gasket and detent solenoid assembly. (Scheme 83) Connect solenoid lead. DO NOT tighten bolts at this time. Install front servo spring and spring retainer in case.

Scheme 83

Scheme 84

REAR SERVO

1. Before installing servo, check band apply pin. See BAND APPLY PIN SELECTION CHECK under «FRONT & REAR SERVO ASSEMBLY»(/gmc/pickup-r1500/1987-1987/remont/automatic-trans/#overhaul-thm-400__front-rear-servo-assembly) under TRANSMISSION DISASSEMBLY. Ensure rear band apply lug is aligned with servo pin bore in transmission case.
2. Lubricate servo bores with transmission fluid. Install rear accumulator spring in servo inner bore. Install rear servo assembly. Ensure it seats properly in bore. With servo depressed, install gasket and cover. Tighten attaching bolts.

CONTROL VALVE BODY ASSEMBLY

1. Install control valve-to-spacer gasket. Install interchangeable governor pipes on control valve assembly. Install governor screen assembly with pointed end up. Install governor oil pipes and control valve assembly.
2. Use care when aligning governor feed pipe over screen. Ensure gasket and spacer plate are not moved out of position and manual valve is indexed properly with pin on detent lever. Ensure governor pipes are seated in case holes.
3. Using 2 guide pins, install control valve assembly and governor pipes on transmission. Be careful when aligning governor feed pipe over screen. Ensure gasket and spacer plate are not moved out of position and manual valve is indexed properly with pin on detent lever. Ensure governor pipes are properly seated in case holes.
4. Start control valve body-to-case bolts. Remove guide pins. Install detent roller and spring assembly. Install and tighten remaining attaching bolts. Tighten solenoid attaching screws.

Install governor assembly into case. Install cover with new gasket and tighten attaching bolts.

Note. Speedometer driven gears come in 3 different tooth sizes. Driven gear and matching sleeve must correspond to axle ratio. Never turn sleeve in transmission case as gear damage will result. Shaft center line is eccentric to outside diameter of sleeve.

Install driven gear into sleeve. Install driven gear assembly into case. Install retainer with tangs in sleeve positioning bosses. Install and tighten attaching bolt.

INTAKE PIPE, FILTER & OIL PAN

Install new intake pipe "O" ring seal. Install pipe into new filter assembly. Place filter and intake pipe in case bore. Install filter retaining bolt and tighten. Install oil pan with new gasket. Install and tighten attaching screws.

Install modulator valve into case with stem end out. Install new "O" ring seal on vacuum modulator. Install modulator into case with vacuum hose pipe facing front and angled 5 degrees toward top of case. Install modulator retainer with curved side of tangs inboard. Tighten attaching bolt.

CONVERTER ASSEMBLY

Install converter onto turbine shaft. Make sure converter hub drive slots are fully engaged with pump drive gear tangs.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• SHIFT POINT SPECIFICATIONS
• REAR UNIT END PLAY CHECK
• FRONT UNIT END PLAY CHECK
• FRONT & REAR SERVO ASSEMBLY