Heavy gearbox 32+32

Heavy gearbox comprises 32 forward speeds and 32 reverse. The transfer shafts and output shafts are supported by tapered roller bearings and are drilled as necessary to pressure-lubricate the bearings, the idler gears and the Hare or Tortoise synchronization system.
The lay shaft is supported at the front by a cylindrical roller bearing and at the rear, by two tapered roller bearings. The main gearbox comprises four synchronized gears. An idler gear on the output shaft positively connected via a double cone synchromesh doubles the four synchronized gears, to give the eight basic speeds.
All pinions are helically cut and in constant engagement. The drive shaft of the direct-drive clutch traverses the layshaft. The input unit assembly located at the front provides four input ratios into the main box.


































Parts list (fig1) 
(1) Input gear (2) Belleville washers (3) Special screw (4) Lube tube (5) Snap ring (6) Spring (7) Transfer shaft (8) Bush (9) Bearing cone (10) Bearing cup (11) Shim(s) (12) Thick shim (13) Driving pinion (2nd(14) Synchromesh cone (2nd(15) Synchro ring (2nd(16) Synchro (1st - 2nd(17) Synchro ring (1st)  (18) Synchromesh cone (1st (19) Driving pinion (1st (20) Bearing cone (21) Bearing cup (22) Bearing cup (23) Bearing cone (24) Driving pinion (4th(25) Synchromesh cone (4th(26) Synchromesh ring (4th(27) Synchro (3rd - 4th(28) Seal ring (29) Snap ring (30) Synchromesh ring (3rd(31) Special washer (32) Synchromesh cone (3rd(33) Bearing cone (34) Bearing cup (35) Driving pinion (3rd) (Hare) (36) Bearing cup (37) Bearing cone (38) Shim(s) (39) Thick shim (40) Tortoise gear (41) Centering pin (43) Bearing cone (44) Bearing cup (45) Shim(s) (46) Rear bearing (47) Output shaft (48) Screw (49) Bearing cup (50) Bearing cone (51) Layshaft (52) Nut (53) Shim (54) Bearing cone (55) Bearing cup (56) Circlip (57) Driven pinion (3rd(58) Spacer (59) Driven pinion (4th(60) Spacer (61) Driven pinion (1st(62) Spacer (63) Shim(s) (64) Driven pinion (2nd(65) Washer (66) Snap ring (67) Needle roller bearings (68) Gearbox housing (69) H/T synchromesh (double cone)


The gearbox drive is provided by input gear (1) integral with transfer shaft (7). The two hubs of synchromesh gears (16) and (27), as well as gear (1) are hard-mounted to transfer shaft (7) by splines. First gear (19) and fourth gear (24) are idler gears on shaft (7). Second gear (13) is an idler gear on bush (8), which is hard-mounted to shaft (7) by splines. Third gear 3rd (35) is installed on tapered roller bearings. All the pinions on layshaft (51) are splined to and rotate with the latter. The gear teeth on shaft (51) mesh with tortoise gear (40) which idles on the output shaft.

Low range (Tortoise)
A synchronized gear is engaged by moving of one of the slides of synchromesh gears (16) or (27) for engage transfer shaft (7) in one of the four idling pinions. Irrespective of the speed selected, the movement is transmitted to layshaft (51). Output shaft (47) is driven by the gear teeth machined on the layshaft intermeshing with tortoise gear (40), engaged to output shaft (47), by moving the slide of synchromesh gear (69) rearwards.

High range (Hare)
This range is selected by forward movement of the slide of synchromesh gear (69), which establishes a direct drive between third gear (35) and output shaft (47). Consequently in 3rd gear, layshaft (51) is passive. The other gears are obtained by moving the slides of synchros (16) or (27) as for the Low range.

Lubrication
The lube oil is supplied from tube (4) connected to the input unit. It circulates in a series of axial channels, one of which crosses the transfer shaft while the other is blind, machined in the output shaft. Radial channels feed the various pinions, the bearings and the Hare or Tortoise synchromesh.
Needle roller bearings (67) are lubricated by an oil film circulating between the direct-drive shaft and the layshaft. The shaft-end bearings on shaft (51) are lubricated by an additional oil flow from the drive bearing of the hydraulic pumps located on the rear-axle intermediate housing, via radial ports drilled respectively in shim (53) and the shaft.


Synchromesh gears single cone (27) (16) (Fig2)



fig2


Locking position
Axial displacement of slide A presses synchronization brake B against friction cone C through the action of balls D and pressure system E. The speed difference existing between the parts being coupled causes a radial rotation limited by pressure system E resulting in turn in a pressure causing the chamfered teeth of synchronization brake B to move against slide A, opposing all relative movement of the latter.


The pressure exerted by slide A and the angular difference of synchronization brake B create an axial pressure between the friction cones of synchronization brake B, and cone C, due to the chamfers of the gear teeth; this axial pressure establishes synchronism by progressive reduction of the speed difference of the parts to connect.


Once synchronism is established, the persistent pressure exerted by slide A against synchronization brake B returns the latter backwards until the teeth of slide A are opposite the recess in synchronization brake B. At this moment, the resistance applied till this point preventing movement of slide A during gear changing is overcome and slide A can thus mesh without noise in the gear teeth of cone C on the gear to be brought into drive.
The rigid connection between the shaft and the gear is now established, and the gears change. If during gear-changing both gears end up tooth-on-tooth, the chamfers machined on the tooth flanks displace the arriving gear until each tooth is opposite a recess.

Neutral position
Slide A is in the central position. The balls are pushed back into the groove at V on slide A by pressure springs F. The pinions are free to turn on the shaft. In this neutral position, slide A is locked by three balls G maintained by springs H.

Overhaul
In the event of removal of the synchromesh gears, check the wear of synchronization brakes B (Fig. 2). Place Cone C on a flat surface and position brake B in abutment by rotating it a few turns under finger pressure (Fig. 3). Measure dimension X at several points using a set of feeler gauges (Fig.2): if a value of less than 0.8 mm is found, check the cone and install a new brake B.

Value of dimension X with brake and new synchromesh cone
- synchro (1st - 2nd) (16): 0.9 to 1.5 mm
- synchro (3rd - 4th) (27): 0.9 to 1.5 mm

Synchromesh gears double cone (69) (Fig.3)



fig3


Locking position
Axial displacement of slide A provides a thrust against ring K, which in turn bears on synchronization brake B, pushing it towards Cone J through the action of balls D, spring F and pressure system E.
When the corresponding pinions are at the required speed, the slide meshes with the coupling flange C of the candidate gear.

Locking of the synchromesh in position (and the neutral position) employ the same principle as for single cone synchromesh gears.

Advantages of the double cone synchromesh
- better reliability
- increased stress strength

Overhaul (double cone)
- If needing to disassemble synchromesh (69), check the wear on synchronization brakes B.
- Proceed by stacking coupling flange C, cone J, synchronization brake B and ring K.
- Position brake B correctly by alternately rotating it through a few turns and applying finger pressure.
- Using a set of feeler gauges, measure dimension at three equidistant points. Take the average of\ the three readings.

Value of dimension 
- on a new synchromesh gear, dimension must be 1.6 mm minimum;
- after operation, if this dimension is less than or equal to 0.60 - 0.80 mm, replace the synchronization brake B.
- Repeat the measurement of using the same process.
- If dimension remains incorrect, also replace ring K and cone J or the complete synchromesh if required.