Overhaul of automatic transmission

Overhaul of AT implies the need to perform a large number of precision measurements, requires the performer to be able to use a special tool and, in view of the foregoing, its implementation lies outside the qualifications of an average amateur mechanic.

For self-confident motorists, this Section provides a brief description of the disassembly and assembly procedures for AT, as well as illustrative material on the design of individual, most typical transmission components.

AT disassembly

Transmission F3А21

Note. It is assumed that the transmission has already been removed from the vehicle and transferred to the assembly stand / workbench.

1. The design of the АТ F3А21 is shown in the illustrations.

2. Before proceeding with the disassembly of the transmission, plug all openings in the crankcase and thoroughly wipe the outer surface of the crankcase. Remove the rotation converter and turn the transmission upside down.

3. Measure the value of the axial play of the input shaft, remove the cover of the distributing shaft and measure the value of the axial play of the latter. Record the measurement results.





4. Remove the start enable switch (see Section Removal, installation and adjustment of the start enable sensor-switch).

5. Remove the oil pan with gasket and filter.

6. Remove the ATF temperature sensor, push the solenoid valve wiring harness grommet and the solenoid valve connector into the transmission case.




7. Disconnect the throttle cable, then remove the mounting bolts and remove the valve assembly.

Attention! Take care not to let the manual valve fall out of the assembly! Do not forget to remove the sealing ring installed between the assembly housing and the transmission housing - the ring must be replaced without fail. Remove the piston and accumulator springs.

8. Remove the rotation converter dome, oil pump assembly, and thrust washer. Remove differential assembly with spacer ring. Remove the AT input shaft assembly with the front and rear clutches.

9. Remove the thrust bearing bush and clutch hubs. Remove thrust washer and bearing. Remove drum and kickdown band. Remove retaining ring, piston, spring and kickdown servo anchor rod.

10. Remove the planetary gear assembly.

11. Remove the wave and return springs, pressure, brake and reaction discs and plates.

Note. Try to remember the installation position of the return spring.

12. Turn out a bolt and remove a lock plate of an axis of an intermediate gear wheel of a distributing mechanism. With a special key (MD998334) remove the intermediate gear. Remove the two inner bearing races and gear spacer.

13. Remove the output flange bearing retainer with O-ring. Remove the circlip from the outer race of the bearing. Remove the inner gear assembly with output flange, transfer drive gear and bearing.

14. Remove the circlip from the rear trunnion of the transfer halyard. Having rested the brass drift against the rear end of the shaft, knock the latter flush with the surface mating with the engine - the driven gear of the transfer mechanism should be removed.

15. Remove the circlip, then (if necessary) Remove the inner and outer races of the tapered roller bearing. Remove the spacer rod stop and manual shaft, remove the steel ball and spring.

F4A20 series transmissions (F4A22/23/33/51)

Note. It is assumed that the transmission has already been removed from the vehicle and transferred to the assembly stand / workbench.

1. The design of the AT series F4A20/30/50 is shown in the illustrations.

2. Before proceeding with the disassembly of the transmission, plug all openings in the crankcase and thoroughly wipe the outer surface of the crankcase. Remove the rotation converter and turn the transmission upside down.

3. Measure the input shaft axial play. Write down the result of the measurement.



4. Remove pulse generators A and B and the PNP switch.

5. Remove the kickdown servo switch.

6. Remove the oil pan with gasket and filter. Remove the ATF temperature sensor.

7. Disconnect the electrical wiring from the solenoid valve and remove the valve assembly.

8. Remove the end cap and the clutch underneath.

9. Remove the end coupling hub, thrust bearing and coupling shaft.

10. Remove the rotation converter dome, oil pump assembly, and thrust washer.

11. Remove differential assembly with spacer ring.

12. Remove input shaft complete with front and rear clutches.

13. Remove the thrust bearing and clutch hub. Remove thrust race and bearing.

14. Remove the kickdown brake band and drum.

15. Remove the retainer, piston, and kickdown servo spring. Remove the anchor rod. Remove the circlip and center stop. Remove the forward and reverse sun gears. Remove the planetary assembly holder with bearing. Remove thrust race and bearing. Remove the wave washer, return spring, pressure plate brake discs/plates and reaction plate, - try to remember the installation position of the return spring.

16. Remove the holder of the mechanical bearing, - if necessary, use a punch.

17. Turn out a bolt and remove a lock plate of an axis of an intermediate gear wheel of a distributing mechanism. With a special key (MD998334) remove the intermediate gear. Remove the intermediate gear shaft and remove the two inner bearing races and the gear spacer.

18. Remove the end bearing circlip. Remove the inner gear assembly with output flange, transfer drive gear and bearing from the crankcase. Remove the transfer shaft cover.

19. Loosen the transfer shaft locknut (the nut has a left-hand thread). Using a press, press out the shaft. Using a puller, remove the transfer shaft bearing. Loosen the set screw and remove the manual control rod with the stop of the spacer rod.

Maintenance of individual components

1. As mentioned above, due to the complexity of the maintenance procedures for AT components during its overhaul, the latter should be entrusted to specialists from a Mitsubishi branded car service station.

2. This Section provides illustrative material that allows the reader with a technical education to get a general idea of the design and assembly and maintenance of individual units and components of an automatic transmission. In addition, some adjustment parameters and dimensional characteristics are given.

ATF oil pump

Make sure that during assembly, the fixing bolts are tightened with the required force; Finally, check the freedom of rotation of the pump gears.

Front clutch

When assembling, make sure that the gap between the retaining ring and the reactive assembly plate meets the requirements Specifications, - retaining rings are available in various thicknesses in the range of 1.6÷3.0 mm in increments of 0.10 mm. don't forget to replace the o-rings.

Rear clutch

Adjustment of the fit clearance of the retaining ring is made by selecting a ring of the appropriate thickness. Make sure the input shaft oil groove is aligned with the reference mark on the clutch holder. Don't forget to replace the o-rings.

Clutch end (F4A20 series transmissions only)

In this clutch, the retaining ring is selected from the thickness range 1.05÷2.05 (pitch = 0.25 mm). Don't forget to replace the o-rings.

Brake assembly low gears and reverse

Don't forget to replace the o-ring.

Planetary assembly

Check that the one-way clutch is seated correctly in the outer race. Tighten all fasteners to the required torque.

Internal gear and transfer case

The nominal thickness of the outlet flange retaining ring is 0÷0.06 mm.

Transfer shaft and control regulator assembly (transmission F3А21)

Make sure that the required fastener tightening torques are met.

Differential

1. When replacing side gears, use spacers of medium thickness (0.93÷1.00 mm).

2. The backlash of gear engagement should be the same in both directions and not go beyond the range of 0.03 ÷ 0.15 mm, - the adjustment is made by selecting distance rings. Rings of the following thickness are produced: 0.75÷0.82 mm; 0.83÷0.92 mm; 0.93÷1.00 mm; 1.01÷1.08 mm and 1.09÷1.16 mm.

Kickdown servo piston

Moisten the components with transmission fluid before assembling.

Speedometer drive gear

The spring-loaded pin, gland and O-ring must be replaced without fail. Lightly lubricate the driven gear with engine oil before installation.

Valve assembly

Note. In no case do not clamp the body of the valve assembly in a vise - the slightest deformation of it can lead to jamming of the valves and the development of leaks! Before installation, thoroughly wash all components in clean ATF and do not wipe them with a rag.

AT F3A21

Disassembly

1. The design of the F3A21 transmission valve assembly is shown in the illustration.

2. Remove the throttle cam assembly. Turn out 13 fixing bolts and remove the lower section of the valve assembly with the lower separating plate.

3. Remove line pressure relief spring and 3 steel balls. Separate the bottom valve assembly and intermediate plate. Remove 4 steel balls from the top assembly. Remove the solenoid valve, reinforcing plate and upper separation plate. Remove the steel ball and spring from the intermediate plate.

Component Status Check and Assembly

1. Thoroughly wash all assembly components in ATF and do not wipe them with a rag afterwards. Check the condition of the working surfaces of the valves and the assembly body.

2. Assess the condition of the valve springs. Measure the height of the springs and compare the result of the measurement with the requirements of the Specifications. Replace if necessary.

3. Lubricate with transmission fluid and reinstall all valves and valve springs. Screw in and tighten the plugs.

4. Track, that all fixing bolts have been tightened with demanded effort. When joining the upper and lower sections of the assembly, be sure to install steel balls and guide pins.

AT series F4A20

Disassembly

1. The design of the valve assembly of transmissions of the F4A20 series is shown in the illustration.

2. Remove the manual and solenoid valves. Remove the clamp retainer. Turn out 13 fixing bolts and remove the lower section of the valve assembly.





3. Remove the separation plate from the intermediate one. Remove the pressure relief spring and remove the two steel balls and oil filter from the intermediate plate. Turn out 8 fixing bolts and remove an intermediate plate from the top section of valve assembly.

4. Remove three steel balls and one Teflon ball from the upper section of the valve assembly, and remove the two retaining clips. Turn out stoppers and take springs and valves.

Component Status Check and Assembly

1. Thoroughly wash all assembly components in ATF and do not wipe them with a rag afterwards. Check the condition of the working surfaces of the valves and the assembly body.

2. Assess the condition of the valve springs. Measure the height of the springs and compare the result of the measurement with the requirements of the Specifications. Replace if necessary.

3. Lubricate with transmission fluid and reinstall all valves and valve springs. Screw in and tighten the plugs. Make sure all mounting bolts are tightened to the correct torque.

Transmission Assembly

Note. Before installation, all components should be lubricated with ATF, and o-rings and seals with technical petroleum jelly. Vaseline can also be used to temporarily fix bearings, thrust races and washers - make sure the components are oriented correctly when installing them into the assembly.

Transmission F3А21

1. Before installation, measure the clearance of the low gear / reverse brake assembly and, based on the measurement results, select a pressure plate of the appropriate thickness (see below).

2. Install reaction and brake plate assembly. Install a pressure plate of the correct thickness. Establish a returnable spring, - trace correctness of installation of a spring.



3. Lubricate with petroleum jelly and install the wave spring in its regular place on the central stop. Place the center stop in the casing and install the circlip. With a DTI dial gauge attached to the rear of the transmission case, determine the clearance of the low/reverse brake assembly, - thread the feeler gauge into the transfer shaft mounting hole so that the plunger is perpendicular to the brake assembly reaction plate.



4. Use a hand pump to inflate the low/reverse brake assembly and read the DTI gauge. By selecting a pressure plate of the appropriate thickness, finish off the required clearance setting (0.80÷1.00 mm).

5. Move the transmission case to a workbench and lay it with the valve assembly mating surface facing up. Load the outlet flange into the crankcase. Secure the flange with a retaining ring, installing the latter on the outside of the crankcase. Fit the transfer case intermediate gear spacer into the crankcase.



6. Install the transfer case idle gear assembly with the shaft. Using the special wrench MD998344, tighten the intermediate shaft.



7. Insert the MD998343 head into the outlet flange and use a torque wrench to measure the flange turning torque. The required value is 0.8 Nm, - if necessary, adjust accordingly by tightening/loosening the shaft tightening force.



8. After adjusting the preload, install the intermediate shaft stop plate. Install the bearing holder, thread the transfer shaft into the assembly and install tool MD998319 on it.

9. Using a special driver, seat the bearing on the transfer shaft, then press the outer race into the crankcase. Establish a conducted gear wheel of a distributing shaft, then plant on a shaft pin a lock ring.



10. Fit thrust race #13 onto flange. Insert planetary carrier with thrust bearing #12 into transmission case. Install both sun gears into planetary carrier.

11. Install the low/reverse brake assembly with the previously seated pressure plate. Install the return spring. Lubricate with petroleum jelly and install the wave spring on the center stop.



12. Fill in the hydraulic holes of the center stop two new sealing rings - before planting, lubricate the rings with transmission fluid.

13. Install the center stop assembly, - make sure that the o-rings and the wave spring do not fall out. Secure the assembly with a retaining ring.

14. Install the kickdown band anchor rod. After replacing the o-rings, install the servo assembly. Fit new o-rings on the inner and outer edges of the servo coupling - note that the rings differ from each other in sectional shape (an O-ring is installed from the inner edge, a D-shaped ring from the outer). Insert the clutch into the transmission case and secure it with the circlip. Install the brake band by attaching the ends to the anchor rod and servo piston rod.

15. Install the drum and seat the brake band on it. Lubricate the #8 thrust bearing with petroleum jelly and seat it on the brake drum of the kickdown servo. Also lubricated with petroleum jelly, install the thrust clip No. 7 on the rear clutch hub.

16. Fit the rear clutch hub onto the planetary sun gear splines and install a #6 thrust bearing from the outside. Install a #2 thrust washer and a #4 thrust bearing from the back of the clutch. Connect the front clutch to the rear and seat the assembly into the transmission case. Install differential.

17. If the axial play of the input shaft measured during dismantling was outside the allowable range, correct it by selecting the thickness of the thrust holder No. 3 and thrust washer No. 1. The required value of the axial play is 0.30 ÷ 1.00 mm.

18. After replacing the gasket, put the oil pump assembly in its regular place. Screw fixing bolts and tighten them with the required effort. Finally, recheck the end play of the input shaft.

19. Lay two pieces of tin solder 10 mm long and 3 mm in diameter on both sides of the outer race of the differential bearing. Place the same pieces of solder on the mating surface of the dome of the rotation converter in the area of the hole for installing the transfer shaft. Install the bearing race into the dome.


20. Install the transducer dome without a gasket and tighten its fastening bolts with a force of 19÷23 Nm.

21. Loosen the bolts, remove the dome and measure the thickness of the flattened pieces of solder. Select the differential spacer according to the formula: solder thickness plus gasket thickness (0.38mm), minus the value of the axial play of the differential (0÷0.15 mm).

22. The thickness of the transfer shaft spacer is determined as follows: Solder thickness plus gasket thickness (0.38mm), plus the bearing preload (0.10÷0.15 mm).

23. Install the appropriate transfer shaft bearing preload adjusting spacer into the converter dome.

Note. Rings are available in thicknesses from 0.82 mm to 1.69 mm in 0.03 mm increments. Install the transfer shaft bearing race. Install the appropriate distance ring on the differential bearing, - the rings are selected from the thickness range of 1.31 - 2.13 mm.

24. Lubricate the knurled areas of the mating surface of the transmission case with silicone grease, then install the gasket. Install the transducer dome. Screw fixing bolts and tighten them with the required effort.

25. Fill in the crankcase until it stops the axis of the manual control lever (without o-ring). Fit the O-ring into the groove protruding from the outside of the crankcase. Pull the axle back slightly and screw in the set screw.

26. Install the spacer rod stop. Install three oil flow O-rings on the valve assembly. Lubricate the accumulator piston cups with ATF and seat the piston in the transmission case. Install the valve assembly in its regular place and tighten the bolts of its fastening with the required force.

27. Install the oil filter. Screw fixing bolts and tighten them with the required effort. After replacing the gasket, install the oil pan with the magnets embedded in it. Tighten the pallet mounting bolts to the required torque. Lubricate the mating surface of the converter with transmission fluid and install the cover on the dome. Measure the distance between the cover and the end of the gear: the installation depth should be approximately 12.0 mm.

F4A20 series transmissions

1. Before proceeding with assembly, measure the clearance of the low gear/reverse brake assembly and select a pressure plate that is appropriate in thickness.

2. Install the reaction plate of the brake assembly, brake plates and discs into the transmission crankcase - make sure that the pressure plate is installed correctly. Install the return spring correctly.

3. Lubricate the wave spring with petroleum jelly and install it on the center stop assembly. Install the center stop in the transmission case and secure it with the circlip. Using a DTI gauge, check the clearance of the low/reverse brake assembly. Activation of the brake assembly is carried out using a hand pump), - select a pressure plate that is appropriate in thickness (the gap size should not go beyond the range of 1.00÷1.20 mm).

4. Remove any previously installed components.

5. Install the transfer shaft bearing outer race into the transmission case. Place the bearings on the shaft, thread the assembly into the crankcase and center it using tool MD998319.

6. Place a spacer ring of maximum thickness on the transfer shaft stub (1.80 mm). Press the transfer shaft driven gear into place. Clamping the shaft pin in a vise, tighten its locknut with the required force (215 Nm).

7. Measure the axial play of the transfer shaft. the measurement result must not fall outside the allowable range (0÷0.025 mm), - select a spacer ring that is appropriate in thickness (rings are produced in the thickness range 1.82÷2.13 mm in increments of 0.06 mm). after adjusting the gap, caulk the locknut.

8. Lubricate the intermediate gear of the distributing assembly and press it against the AT crankcase. Install the two tapered roller bearings, thread the idler gear/bearing assembly into the crankcase and thread the shaft through it from the outside.

9. Tighten the idler shaft with tool MD998344. Insert the MD998906 head into the outlet flange and use a torque wrench to measure the flange turning torque. The required value is 0.8 Nm, - if necessary, adjust accordingly by tightening/loosening the shaft tightening force.

10. After adjusting the preload, install the intermediate shaft stop plate. Install the bearing holder, screw in new screws and tighten them to the required torque.

11. Fit the #12 thrust bearing planet carrier into the transmission case. Install the #9 thrust bearing and #10 cage onto the forward sun gear. In the same manner, assemble the reverse sun gear and install it into the carrier.

12. Install the low/reverse brake assembly with pressure plate selected and seated earlier. Install the return spring. Lubricate with petroleum jelly and install the wave spring on the center stop. Fill two new O-rings into the hydraulic holes of the center stop - before landing, lubricate the rings with transmission fluid.

13. Install the center stop assembly, - make sure that the o-rings and the wave spring do not fall out. Secure the assembly with the retaining ring, making sure that the lock of the latter is not turned towards the fixing hole of the pulse generator A.

14. Install the kickdown band anchor rod. Place new O-rings on the servo piston - note that the rings differ from each other in diameter and cross-sectional shape. Fit a new O-ring into the groove on the coupling. Insert the spring, piston and servo clutch into the transmission case and secure the assembly with the circlip. Install the brake band by attaching the ends to the anchor rod and servo piston rod.

15. Install the drum and seat the brake band on it. Lubricate the #8 thrust bearing with petroleum jelly and seat it on the brake drum of the kickdown servo. Also lubricated with petroleum jelly, install the thrust clip No. 7 on the rear clutch hub.

16. Fit the rear clutch hub onto the planetary sun gear splines and install a #6 thrust bearing from the outside. Install a #2 thrust washer and a #4 thrust bearing from the back of the clutch. Connect the front clutch to the rear and seat the assembly into the transmission case. Install differential.

17. If the axial play of the input shaft measured during dismantling was outside the allowable range, correct it by selecting the thickness of the thrust holder No. 3 and thrust washer No. 1. The required value of the axial play is 0.30 ÷ 1.00 mm.

18. After replacing the gasket, put the oil pump assembly in its regular place. Screw fixing bolts and tighten them with the required effort. Finally, recheck the end play of the input shaft.

19. Lay two pieces of tin solder 10 mm long and 3 mm in diameter on both sides of the outer race of the differential bearing. Install the transducer dome without a gasket and tighten its fastening bolts with a force of 19÷23 Nm.

20. Loosen the bolts, remove the dome and measure the thickness of the flattened pieces of solder. Select the differential spacer according to the formula: solder thickness plus gasket thickness (0.38mm), minus the value of the axial play of the differential (0÷0.15 mm).

21. Install the appropriate distance ring on the differential bearing, - the rings are selected from the thickness range of 1.85 ÷ 65.28 mm in increments of 0.09 mm.

22. Lubricate the knurled areas of the mating surface of the transmission case with silicone grease, then install the gasket. Press the transducer dome against the transmission. Screw fixing bolts and tighten them with the required effort.

23. Install the clutch shaft (long, splined stud towards the transducer) Place a thrust washer on the end of the clutch return spring.

24. By supplying air to the appropriate fittings, check the proper functioning of the clutches.

Attention! Only absolutely dry air is allowed to be pumped into the transmission! Do not pressurize the transmission higher than 1.75 kgf/cm².

25. Fill in the crankcase until it stops the axis of the manual control lever (without o-ring). Fit the O-ring into the groove protruding from the outside of the crankcase. Pull the axle back slightly and screw in the set screw. Install the detent ball and spring.

26. Install the spacer rod stop. Lubricate the accumulator piston cups with ATF and seat the piston in the transmission case. Install the brake assembly oil flow sealing ring from above in the central part of the valve assembly and seat the latter in its regular place. Screw and tighten with the required effort fixing bolts.

27. Install the oil filter. Screw fixing bolts and tighten them with the required effort. After replacing the gasket, install the oil pan with the magnets embedded in it. Tighten the pallet mounting bolts to the required torque. After replacing the o-ring, install the kickdown servo switch in its original place and fix it with a retaining ring. Install the PNP switch and manual control lever.

28. Adjust the start enable switch (PNP). Install pulse generators A and B. Lubricate the mating surface of the converter with transmission fluid and install the cover on the dome. Measure the distance between the cover and the end of the gear: the installation depth should be approximately 12.0 mm.