Gearbox – Layshaft

The layshaft and its pinions form the upper transmission line of the Heavy gearbox with mechanical reverse shuttle or Power shuttle. Shaft (51) bears, in this order, the driving pinions of 2nd gear (64), 1st gear (61), 4th gear (59) and 3rd gear (57). These pinions are splined to the shaft and separated by spacers (62) (60) and (58). Axial clearance of the gear train is provided by one or more shims (63). The rear teeth of the layshaft (51) continuously engage the Tortoise pinion mounted on the output shaft. The front of the shaft is supported by a roller bearing fitted to the rear of the input unit. Its rear extremity is supported by two taper roller bearings (49) (50) and (54) (55).
The adjustment of these bearings is of the "Semi Set Right" type. It is carried out by placing a shim (53between the bearing cones (50) (54) in order to obtain a clearance of a predetermined value between the cups (49) (55).

Special points
- The friction ring (76) forms an oil tight link of the upper shaft line between the gearbox and the intermediate housing. It is adjusted and sealed with Loctite 648 or its equivalent in the rear bore of the shaft (Fig. 6).
- Shim (53) has several radial ports permitting lubrication of bearings (49) (50) and (54) (55).

Parts list
(49) Bearing cup (50) Bearing cone (51) Layshaft (52) Nut (53) Shim (54) Bearing cone (55) Bearing cup (56) Circlip (57) 3rd gear driven pinion (58) Spacer (59) 4th gear driven pinion (60) Spacer (61) 1st gear driven pinion (62) Spacer (63) Shim(s) (64) 2nd gear driven pinion (65) Washer (66) Snap ring (67) Needle bearing (76) Friction ring with shoulder

To take out the layshaft it is necessary to remove the gearbox.
Uncouple the tractor between the gearbox and the intermediate housing.
Separate the gearbox from the engine. Take off the selector cover.
Place the gearbox on a suitable fixture. Remove the input unit.
Disassemble the selector rails and the forks.

Where necessary, immobilise the gear train in the gearbox. Unlock and slightly loosen nut (52) with the aid of an appropriate chisel in order to overcome the resistance of the Loctite.
- Of course, this nut is replaced during reassembly. This operation facilitates the removal of the nut with the service tool once the output shaft and mainshaft have been disassembled.
Remove the output shaft. Remove the mainshaft.

Removing and disassembling the layshaft

Finish unscrewing the nut (52) using service tool and remove bearing cone (50).
Keep the bearing cups and cones together if they are to be re-used.
Take out the shaft (51) and pinion assembly.
Remove the shim (53) and take off the cone (54).
Where necessary, drive off the cups (49) (55) and mark their locations.
On shaft (51) remove the snap ring (66) and washer (65) and mark the locations. Take off the 2nd gear pinion (64), shim(s) (63), spacer (62), 1st gear pinion (61), spacer (60), 4th gear pinion (59), spacer (58), 3rd gear pinion (57) and circlip (56).
If necessary, drive off needle bearing (67).

Reassembling and install the Layshaft

Clean and inspect the components. Replace the defective parts.
On the shaft, check that the lubricating ports leading to the bearing cones (50) (54) are not blocked. Check for the presence of friction ring (76).
If disassembled, insert the needle bearing (67) to thrust against the shoulder of shaft (51) with the aid of a suitable fixture.
Check that the needle bearings turn freely in the cage after insertion.
Install a new circlip (56). Replace the 3rd gear pinion (57), spacer (53), 4th gear pinion (59), spacer (60), 1st gear pinion (61) and spacer (62). Replace 2nd gear pinion (64) without the shims (63). Carry out the shimming of the pinions. Shim the pinions.
- If necessary, shim the bearings (54) (55) and (49) (50).
Lubricate the cones (50) (54) and the bearing cups (49) (55).
If disassembled, insert the cups to thrust against the shoulder of the housing, with large cup (49) fitted into the rear bore of the gearbox.
Slide cone (54) onto shaft with shim (53) the thickness of which has been determined at operation 46.
Place the assembled shaft in the housing. Install cone (50). Pre-tighten nut (52) in contact with the cone (50).
- This nut will be definitively tightened to torque once the input unit has been refitted, in order to obtain the correct alignment of the layshaft in the two bearings.
Reassemble the layshaft. Reassemble the output shaft. Install the input unit.

- Tighten nut (52) to a torque of 50 Nm. Rotate the layshaft several times to progressively seat the bearings. Carry out final tightening of the nut to a torque of 100 - 150 Nm, the threads having previously been lightly smeared with Loctite 270 or equivalent.
- Lock the nut by bending the collar without breaking it into grooves "R" on the shaft with the aid of an appropriate pin punch.
Reassemble and adjust the gear selector device.
Install the selector cover.
Check that the gears change correctly and that the Hare / Tortoise position functions.
Couple the gearbox to the engine.
Couple the tractor between the gearbox and the intermediate housing.
Check the oil tightness of seals and hydraulic unions.
Road test the clutch controls, the A, B, C, D ratios of the Dynashift mechanical reverse shuttle or power shuttle, the gears and the Hare / Tortoise range.

Shimming the pinions 

The pinions must be stacked with the shims (63) temporarily removed.
Using a set of feeler gauges, measure the distance between the 2nd gear pinion (64) and spacer (62).

In relation to the measurement, determine the required thickness of the shim(s) (63) in order to obtain a clearance of: J1 = 0.02 to 0.31 mm

If possible, preferably shim towards the nominal tolerance.
Remove snap ring (66) and washer (65). Remove the 2nd gear pinion.
Slide the previously selected definitive shims on to the shaft. Refit the pinion and washer (65), turning the chamfer to the exterior. Install a new snap ring (66) and check that it is correctly positioned.

Install the assembled shaft with its pinions into the gearbox housing. Carry out the remaining

Shimming the bearings

- The principle consists in defining the thickness of the shim (53) to be fitted between the bearing cones (50) (54) under load (500 N) and in order to obtain an "X" measurement of 8.60 to 8.68 mm between cups (49) (55) mounted loose.

- Bearings will be shimmed before refitting the layshaft. If the removed bearings which, extract cups (49) (55) from the gearbox housing when pairing them with their respective cones.

Preparation for shimming 

Install bearing cones (50) (54) and cups (49) (55) without shim (53) on service tool, ref. 3378263M11. Tighten the tool in a vertical position in a vice.
Compress the spring until the shoulder of the special bolt is in contact with the top of the tool.
Special point
The spring characteristics and the length of the bolt shoulder provide the correct load to apply to the
Turn cylinder "C" several times, in order to correctly seat the cones in the cups.


Measure the distance between the bearing cones (50) (54). Position the pressure plate of the tool on the face of the cone (54). Place the index of the dial gauge on the extremity of the pressure plate.

On the dial gauge:
- set the long hand to zero
- note the position of the short hand

Turn the pressure plate half a turn while maintaining it on the face of the cone (50). Immobilise the rod by moderately manually tightening the stop bolt.
In relation to the measurement noted on the dial gauge, select the corresponding shim (53) to be definitively fitted between the bearing cones (50) (54).
Carry out the remaining operations.