Synchromesh transmission with end plates, shift rods and shift forks (late version)


 12-speed synchromesh transmission is similar except that a spacer and shims are used In place of washer and snap ring to locate components on Input shaft

1.Snap ring, 2.Shim, 3.Snap ring, 4.Bearing, 5.Outer spacer, 6.Inner spacer, 7.Bearing, 8.Input gear, 9.Sliding cellar, 10.Snap ring, 11.Collar gear, 12.Slow range gear, 13.Thrust washer, 14.Snap ring, 15.Snap ring, 16.Bearing, 17.Retaining collar, 18.Split rings, 19.Low range gear, 20.Sliding collar, 21.Front sliding collar gear, 22.Snap ring, 23.Rear sliding collar gear, 24.High range gear, 25.Splined washer, 26.Snap ring, 27.Bushing, 28.Bearing pad, 29.Bearing pad, 30.Bearing pad, 31.Input shaft, 32.Reverse idler gear & hushing, 33.Spacer, 34.Bearing, 35.Snap ring, 36.Lubrication bracket, 37.Stud, 38.Nut, 39.Locknut, 40.Washer, 41.Bearing, 42.Spacer, 43.Front end housing, 44.Snap ring, 45.Shim, 46.Splined washer, 47.Bearing pad, 48.Snap ring, 49.Centralizer spring, 50.Second gear, 51.Retaining washer, 52.First/reverse sliding gear, 53.Center housing, 54.Retaining washer, 55.Tab washer, 56.Bolt, 57.Rear end housing, 58.Shoulder washer, 59.Spacer, 60.Third gear, 61.Front synchronizer gear, 62.Synchroniser, 63.Bearing pad, 64.Split rings, 65.Shim, 66.Bearing, 67.Pinion shaft, 68.Shift interlock plug, 69.Second/third shift rod, 70.First/reverse shift rod, 71.Idler shaft, 72.Roll pin, 73.Plug, 74.Thrust washer, 75.Bearing, 76.Spacer, 77.Idler gear, 78.Bearing, 79.Thrust washer, 80.Bearing, 81.Intermediate shaft, 82.Bearing,  83.Shim, 84.Slow/normal shift rod, 85.High/low shift rod, 86.Spacer, 87.Shim

Place transmission in a suitable transmission support stand. Drive roll pins from slow/ normal shift rod (84), shift fork and selector jaw. Use a soft metal rod to drive shift rod toward rear of transmission just far enough to remove detent ball and spring. Remove slow/normal shift rod.
Remove roll pins from high/low shift rod (85), shift fork and selector jaw. Drive shift rod toward rear of trans-mission just far enough to remove detent ball and spring, then remove shift rod and selector jaw.
Remove second/third shift rod (69), shift fork, selector jaw, detent ball and spring and shift interlock plug (68).
Note that pinion nut (39) has left-hand threads, then remove nut (39), washer (40) and bearing cone (41). Remove snap ring (1) and spacer (2). The row of smaller gear teeth on input gear (8) has a missing tooth. Align this gap with a gear tooth on slow/normal idler gear (77) and remove input gear and bearing assembly.

Remove nuts from stud bolts and raise front end housing (43) approximately 40 mm (1.5 inches). Use blocks to support front end housing in this position.
Push first/reverse shift rod (70) toward rear of transmission just far enough to remove detent ball and spring. Remove sliding collar (9), snap ring (10) and collar gear (11). Remove slow range gear (12), the six bearing pads (28) and thrust washer (13). Remove front end housing (43).
Remove roll pin (72) and idler shaft (71). Remove thrust washers (74 and 79) and idler gear (77). To disassemble input gear (8), remove snap ring (3). Press bearings (4 and 7) and spacers (5 and 6) off input gear (8). Remove remaining bearing cups, snap rings and spacers from front end housing.
Remove stud bolts and rotate center housing (53) toward countershaft (81) to gain gear clearance and remove center housing. Remove countershaft (81) and press bearings (80 and 82) off as necessary.
Remove retaining bolts (56) and high/low shift fork from sliding collar (20). 

Remove input shaft (31) using care not to lose retaining washer (54). Remove snap ring (35) and press A, bearing (34), spacer (33) and reverse idler gear (32) off together. Remove snap ring (14), bearing (16), retaining collar (17) and split rings (18). Remove low range gear (19), the six bearing pads (29) and front sliding collar gear (21). Remove sliding collar (20), snap ring (22) and rear sliding collar gear (23). Remove high range gear (24) and the six bearing pads (30). Remove splined washer (25) and snap ring (26) on 1690 models. Remove spacer (86) and shims (87). On all models, remove bushing (27) from input shaft if necessary.
Remove second/third shift fork from synchronizer. Remove spacer (58), shims (45), spacer (59) and thrust washer (46). Remove third gear (60) and the six bearing pads (47), Remove synchronizer assembly (62) and front synchronizer gear (61). Remove snap ring (48) and rear synchronizer gear (not shown). Remove second gear (50) and the six bearing pads (63). Remove retaining collar (51) and split rings (64). Remove first/reverse sliding gear (52) and shift rod assembly (70).
If pinion shaft (67) or bearing (66) are to be renewed, mark bearing caps and remove differential assembly. Remove pinion shaft, rear bearing and shims from rear end housing.


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 (47 and 63) for wear. Pads should slide easily into their grooves with no binding, but should not be excessively loose. No attempt should be made to disassemble synchronizer assembly as individual service parts are not available. Check detent balls and shift rail grooves for wear. There should be a small clearance between ball and bottom of groove. Check all thrust washers and spacers for excessive wear and renew as necessary.


If pinion shaft, pinion shaft bearings or transmission housings are renewed, the pinion shaft protrusion must be set before reassembling transmission.
If countershaft (81), bearings (80 and 82) or transmission housings are renewed, shaft end play must be set as follows: 
Remove bearing cup from rear housing and subtract 0.20 mm (0.008 inch) thickness shims from original shim pack. Reinstall bearing cup with shims and assemble countershaft, center housing (53) and front end housing (43), Tighten stud nuts to 95 N- m (70 ft.-lbs.) torque. Rotate shaft to be sure bearings are properly seated.

Position a dial indicator so probe contacts face of rear gear, then move shaft up and down and measure end play. Correct end play is 0.05-0.10 mm (0.002-0,004 inch). Remove countershaft and rear bearing cup and install shims (83) as necessary to provide correct end play.


- input shaft rear bearing (34) in rear housing (57) and hold in place with retaining washer (54), tab washer (55) and bolt (56). Assemble pinion shaft (67) and rear bearing (66) into position in rear housing.
- center housing (53) so front face of housing is even with ends of bottom studs. Place first/re verse sliding gear (52) on shaft with selector fork groove towards rear housing. 
- washer (51) with recessed side towards gear (52). Slide second gear (50) onto shaft, put a small amount of grease on bearing pads (63).
- pads into splines between shaft and gear. Position rear synchronizer gear (not shown) with thin part of teeth towards front of pinion shaft. Slide snap ring (48) onto shaft but not into groove. 
- front synchronizer gear (61) with thin part of teeth towards the rear, aligning mark on side of gear with mark on side of rear gear. 
- synchronizer (62) over the gears.
- second/third shift rod assembly (69) into groove of synchronizer. 
- first/reverse shift rod assembly (70) into groove of sliding gear (52). Enter end of first/reverse shift rod into hole in rear housing, then move center housing (56) and shift rod rearward together about 50 mm (2 inches). Position split ring (64) into groove in shaft and slide washer (51) over split ring. Push all parts rearward until snap ring (48) is seated in shaft groove.
- third gear (60), put a small amount of grease on bearing pads (47) and insert pads into splines between gear and shaft. 
- splined washer (46) and spacer (59).


Assemble components onto input shaft (31) in reverse order of removal while observing the following special instructions.
Shims (87) are installed as necessary to remove all end play of components on the shaft. Components are located on shaft by snap ring (26); there is no provision for adjustment of end play. Rear sliding collar gears (21 and 23) have lubrication slots and a punch marked tooth for alignment on one side of each gear. 
- rear gear (23) so slotted side is facing high range gear (24) and punch marked tooth is aligned with input shaft spline that has a hole in it. 
- snap ring (22) and sliding collar (20). 
- front sliding collar gear (21) with side having slots facing away from snap ring (22) and align punch marked tooth with punch marked tooth of rear gear (23). The sliding gear splines will engage sliding collar splines when correctly installed.
- low range gear (19) with smaller gear teeth toward sliding collar gear (21). Lubricate and install the six bearing pads (29) in input shaft splines under low range gear. 
- split ring (18), retaining collar (17) and bearing (16). Be sure bearing is installed with side stamped with bearing number facing front end of shaft. Bearing must seat against retaining collar.
- reverse idler gear (32) with bushing on input shaft making sure side with beveled gear teeth is towards front of shaft. 
- thrust washer (33) with flat side against reverse idler gear. Drive input shaft into rear bearing (34) and end housing (57) until snap ring (35) can be installed. 
- lubrication bracket (36), but do not tighten mounting bolts at this time.


To adjust counter shaft end play, first measure width of shoulder on front of countershaft. If shoulder width is 1.5-1.73 mm (0.060-0.068 inch), shims (83) should be installed in front end housing. If shoulder width is 3.33 3.58 mm (0.131-0.141 inch), shims should be installed in rear end housing.
Assemble countershaft, center housing and front housing. Tighten stud nuts to95N-m (70ft.-lbs.) torque. Turn countershaft in both directions to seat bearings. Mount a dial indicator so probe is against end of countershaft, then move shaft up and down and measure end play. Correct end play is 0.05-0.10 mm (0,002-0.004 inch).
Remove countershaft from gearbox. Remove bearing cup from front or rear end housing and install shims as required between the bearing cup and end housing to provide specified end play. Reinstall bearing cup and counter-shaft.
Place second/third gear shift fork in synchronizer groove. Place high/low shift fork in groove on high/low sliding gear. Reinstall center housing.


- bearings (75 and 78) and spacer (76) into idler gear (77). Both bearings should be 0.25-1.3 mm (0.010-0.050 inch) below outer surfaces of idler gear when installed. 
- idler shaft assembly and thrust washers in front end housing (43) with large gear towards the front. Push idler shaft (71) into idler gear aligning spring pin holes in shaft and front housing. 
- spring pin (72).
- detent springs and balls for first/reverse and second/third into end housing. - front end housing onto the bottom studs. Assemble splined washer (13) and slow range gear (12) onto input shaft with smaller gear teeth towards the front. Lubricate and install the six bearing pads (28) between shaft splines and range gear. 
- sliding collar gear (11) and sliding collar (9). Insert first/reverse shift rod into front end housing using tool to depress detent ball and spring. Insert second/third shift rod into front housing using tool to depress detent ball and spring. 
- high/low shift rod. 
- roll pins in shift forks.
- snap ring (10) on front of input shaft (31). Align input shaft, countershaft and pinion shaft with end housing, then position front end housing down against center housing. Tighten end housing retaining nuts to 95 N-m (70 ft.-lbs.) torque.
- slow/normal shift fork into groove of sliding collar (9). Push shift rod rearward through shift fork and selector jaw, align pin holes and install spring pins. 
- safety start switch balls and plungers.
- bearing (7) on input gear (8) with thick edge of outer race facing away from gear. 
- spacers (6 and 5). 
- outer bearing (4) so snap ring groove on outer race is towards front splined end of input gear. 
- snap ring (3). Align gap in teeth of input gear with tooth of idler gear, then push input gear assembly into front housing until spacer (2) and snap ring (1) can be installed.


spacer (59) and all shims (45) removed during disassembly plus an additional 0.25 mm (0.010 inch) thick shim. 
- shoulder washer (58) with flat side against shims. 
- bearing cone (41), washer (40) and nut (39). Tighten nut to 270 N-m (200 ft.-lbs.) torque. Mount a dial indicator so probe contacts end of pinion shaft and measure shaft end play.

Remove  nut,  washer,  bearing  and shoulder washer. Remove thickness of shims (45) equal to measured end play plus an additional 0.05 mm (0.002 inch). This will provide recommended preload of 0.05 mm (0.002 inch). Reinstall spacer, bearing, washer and nut and tighten nut to 270 Nm (200 ft.-lbs.) torque. Shift transmission and range section through all gears and check to be certain all gears and detents work properly.