Synchromesh transmission with end plates, shift rods and shift forks - overhaul


DISASSEMBLY

 12-speed synchromesh transmission

1.Snap ring, 2.Snap ring, 3.Bearing, 4.Snap ring, 5.Inner sparer, 6.Outer spacer, 7.Bearing, 8.Input gear, 9.Sealing ring, 10.Slow/normal sliding gear, 11.Snap ring, 12.Bearing, 13.Spacer, 14.Snap ring, 15.Bushing, 16.High/law sliding gear, 17.Input shaft, 15.Bushing surface, 19.Bushing, 20.Reverse idler gear, 21.Retaining washer, 22.Tab washer, 23.Bolt, 24.Thrust washer, 25.Bearing, 26.Snap ring, 27.Locknut, 28.Wisher, 29.Bearing, 30.Spacer, 31.Front end housing, 32.Snap ring, 33.Shims, 34.Thrust washer, 35.Bearing pad, 36.Snap ring, 37.Synchronizer, 38.Second gear, 39.Retaining washer, 40.Split rings, 41.Shim, 42.Rear end housing, 43.Bushing, 44.Shim, 45.Mounting bolt, 46.Shoulder spacer, 47.Washer, 48.Third gear, 49.Front synchronizer gear, 50.Synchronizer spring, 51.Bearing pad, 52.First/reverse sliding gear, 53.Bearing, 54.Pinion shaft, 55.Shift interlock, 56.Center housing, 57.Second/third shift rod, 58.First/reverse shift rod, 59.Idler shaft, 60.Roll pin, 61 Plug, 62.Thrust washer, 63.Bearing, 64.Spacer, 65.Idler gear, 66.Bearing, 67.Thrust washer, 68.Bearing, 69.Countershaft, 70.Bearing, 71.Shim, 72.Slow/normal shift rod, 73.High/low shift rod, 74.Shift fork, 75.Selector jaw, 76.Sleeve

Place transmission in a suitable transmission support stand, then remove roll pins from slow/normal shift fork (74) and selector jaw (75). Push slow/normal shift rod (72) rearward just far enough to remove detent ball and spring. Remove shift rod, selector jaw and shift fork. Remove high/low shift fork, sleeve, detent ball and spring and shift rod (73). Remove roll pins from shift fork and selector jaw on second/third shift rod (57) and move rod toward rear of transmission just enough to remove detent ball and spring. Remove shift interlock plug (55).

Noting pinion nut (27) has left-hand threads, remove nut (27), washer (28) and bearing cone (29) from pinion shaft (54). Remove stud bolt nuts, then separate and support front end housing (31) approximately 40 mm (1.5 inches) from transmission center housing (56). Push first/reverse shift rod (58) rearward just enough to remove detent ball and spring. Lift front end housing (31) off transmission center housing (56). Remove slow/normal sliding gear (10) from inside front end housing.

Remove roll pin (60) and remove idler shaft (59). Remove snap ring (1) from input gear (8) and snap ring (2) from front end housing (31). Carefully remove input gear assembly out of front end housing. Do not use force as dam-age to bearings may result. Remove idler gear (65) and both thrust washers (62 and 67). Remove bearings (63 and 66) and spacer (64) from inside idler gear (65). Remove input gear bearing cup and outer spacer (6) from front end housing. Remove remaining bearing cups, spacer, bearings and snap rings as necessary.
Remove stud bolts. Remove center housing (56) by rotating center housing towards countershaft to gain clearance, then lift housing over shaft and gear assemblies.

Remove countershaft (69) from rear end housing (42). Remove retaining bolt (23), remove high/low shift fork from sliding gear (16), and remove input shaft assembly (17) from rear end housing. Use care not to lose retainer (21). Remove snap ring (26) and press rear bearing (25), thrust washer (24) and reverse idler gear (20) off together. Move snap ring (14) away from bearing (12) and press bearing and spacer (13) off input shaft (17). Remove snap ring (14) and high/low sliding gear (16). Remove bushing (15) from inside input shaft.

Remove second/third shift fork from synchronizer (37). Remove shoulder spacer (46), shims (33), spacer (47) and third gear thrust washer (34). Remove third gear (48) and the six bearing pads (35). Remove synchronizer (37) and front synchronizer gear (49). Remove snap ring (36) and gear synchronizer gear (not shown). Remove second gear (38), the six bearing pads (51), split ring retainer washer (39) and split rings (40). Remove first/reverse sliding gear (52) and shift rod assembly together.
If pinion shaft (54) is to be renewed, mark differential bearing cap positions and remove differential assembly. Remove pinion shaft rearward from housing.

INSPECTION

Clean and inspect all parts. Examine bearings and bushings for wear or damage and renew as necessary. If gear teeth show excessive wear or irregular wear pattern, gear should be renewed along with its mating gear.
Examine synchronizer friction surfaces and the synchronizer pads (35 and 51) for wear. Slight looseness of pads in synchronizer is normal and the pads should slide easily into their grooves with no binding. No attempt should be made to disassemble synchronizer assembly as individual service parts are not available.


Examine fit of detent balls in grooves of shifter rails. Shift rail grooves should have straight 60 degree sides and detent ball must not contact bottom of groove. Check all thrust washers and spacers for excessive wear or damage and renew as necessary.

REASSEMBLY

If pinion shaft, bearings, end housings or center housing are renewed, pinion shaft protrusion must be set before reassembling transmission.

PINION SHAFT ASSEMBLY

Install: 
- pinion shaft and rear bearing sliding gear (16) on input shaft with larger diameter gear toward rear end of shaft. Heat front bearing (12) to 120°C (250°F) maximum, then install snap ring (14), spacer (13) and bearing on shaft. Note that bearing must be installed with side stamped with bearing numbers towards front end of shaft. Press new bushing (19) into reverse idler gear (20), then install gear onto input shaft with beveled edge of gear teeth towards front of shaft. 
- thrust washer (24) with flat side towards idler gear. Heat rear bearing (25) to 120°F (250°F) maximum, then install bearing and snap ring (26).
Position shaft assembly on rear housing and install retaining washer (21), tab washer (22) and bolt (23). Tighten bolt to 11 N-m (8 ft.-lbs.) torque, then bend tab washer against bolt head.

INPUT SHAFT ASSEMBLY

Install: 
- new bushing (15) into front end of input shaft (17). Place high/low into rear housing. Position first/reverse shift fork into slot in sliding gear (52), then install gear over pinion shaft. Make certain shift rod enters hole nearest input shaft retaining washer. 
- split rings (40) and retaining washer (39). 
- second gear (38) with synchronizer ring towards front end of shaft. Lightly coat bearing pads (51) with grease, then install pads in pinion shaft splines under second gear. 
- rear synchronizer gear so end of gear with alignment marks is towards second gear. 
- snap ring (36), align marks of rear synchronizer gear with marks on front synchronizer gear.
- front gear (49) with slotted end of gear towards front of shaft. 
- synchronizer (37). 
- third gear (48) with synchronizer ring towards synchronizer. Apply small amount of grease to bearing pads (35), then install pads behind third gear.
- thrust washer (34) and fiat spacer (47). Do not install shims (33) or shoulder spacer (46) at this time.

COUNTERSHAFT ASSEMBLY

Heat front and rear hearings (68 and 70) to 120°C (250°F) maximum, then install on countershaft (69).
To adjust end play, remove a shim 0.25 mm (0.010 inch) in thickness from original shim pack (71). 
Install: 
- remainder of shims and bearing cup in rear housing. 
- front bearing cup in bore of front housing. Position countershaft on rear housing. 
- center housing, stud bolts and front housing and tighten stud bolt nuts to 95 Nm (70 ft.-lbs.) torque. Mount a dial indicator so probe contacts rear gear of countershaft. Move shaft up and down and measure end play. Disassemble housings and countershaft. Remove rear bearing cup and shims. Subtract 0.076 mm (0.003 inch) from end play measurement. The result is thickness of shims that must be added to original shim pack to obtain specified end play of 0.076 mm (0.003 inch). 
- required thickness of shims and reinstall bearing cup. Position countershaft on rear housing.

CENTER AND FRONT HOUSING ASSEMBLIES

To install: 
- center housing (56), place second/third gear selector fork into groove on synchronizer (37). Put high/low selector fork into groove on sliding gear (16). 
- center housing turning the housing to clear countershaft gears. Apply Loctite 242 to stud bolt threads, then install stud bolts into rear housing and tighten to 122 N-m (90 ft.-lbs.) torque.        
Heat bearing (7) to 120°C (250°F) maximum, then install on input gear (8). Be sure side of bearing stamped with bearing numbers is towards splined end of gear. 
- inner spacer (5) on input gear. 
- snap ring (4), bearing (3) and snap ring (2) in front housing (31). 
- outer spacer (6) and outer bearing race for roller bearing in front housing. Assemble bearings (63 and 66) and spacer (64) in range idler gear (65). Use a depth micrometer to measure distance needle bearing cage is below free of idler gear. The distance must be 0.25-1.27 mm (0.010-0.050 inch). If distance is not within the specified range, check for worn needle bearings. Renew spacer if spacer length is less than 42.545 mm (1.675 inches).
- assembled range idler gear and thrust washer (62 and 67) in front housing with larger gear towards front of the housing. 
- input gear assembly in front housing and install snap ring. Clean oil passage in idler gear shaft (59), apply Loctite 242 to threads of plug (61) and install plug in shaft. Align roll pin hole in idler shaft and front housing.
- install shaft through idler gear and roll pin. Assemble snap ring (32), spacer (30) and pinion shaft front bearing cup into bore in front housing. 
- front housing assembly and support housing approximately 40 mm (l'/a inches) above center housing. Place slow/normal sliding gear (10) on rear input shaft (17) with selector fork groove towards input gear. Remove spacers, then lower front housing until first/reverse shift rod (58) enters hole in front housing. 
- detent ball and spring using tool while joining front housing and center housing. 
- new locknuts on housing studs and tighten to 95 N-m (70 ft.-lbs.) torque.

SHIFT RODS AND DETENTS

Install: 
- high/low shift rod (73) and spacer (76). Install detent spring and ball using tool. 
- roll pin in shift fork.
- slow/normal shift rod (72), shift fork (74), spacer and selector jaw(75).
- detent spring and ball using assembly tool, then install roll pins in fork and selector jaw.
- second/third shift rod making certain end with neutral start switch groove is toward rear of transmission. Push rod through shift fork slightly.
- selector jaw with flat side toward first/reverse selector jaw. 
- shift interlock plug (55) and detent ball and spring.
Engage third gear and install roll pin in second/third selector jaw. Engage second gear and install roll pin in second/third shift fork.

PINION SHAFT BEARING PRELOAD

Install: 
- original shims (33) removed during disassembly plus an additional 0.25 mm (0.010 inch) thick shim. 
- shoulder washer (46) with flat side against shims (33). 
- bearing cone (29), washer (28) and nut (27). Note that nut has left-hand threads and tighten to 270 N-m (200 ft.-lbs.) torque. Mark differential bearing caps and remove differential assembly if not already removed. Mount dial indicator so probe contacts end of pinion shaft, then measure and note amount of pinion shaft end play. 

Remove nut (27), washer (28), bearing (29) and shoulder washer (46). Remove thickness of shims (33) 0.05 mm (0.002 inch) greater than amount of measured end play to obtain specified bearing preload of 0.05 mm (0.002 inch). Reinstall spacer, bearing, washer and nut. Tighten nut to 270 N-m (200 ft.-lbs.) torque. Reinstall differential assembly and adjust backlash.
Shift transmission and range section through all gears and check to be certain all gears and detents work properly.