Heavy gearbox - selector rails


Tractors fitted with a Heavy gearbox, the selector rails used for gear selection are located on the right-hand side of the gearbox behind the control cover. The gear selector comprises four selector rails of which three are for the gearbox and one for the input unit. Each selector rail supports its own fork and respective selector and moves longitudinally in end-bearings. The forks are adjustable, thus ensuring a functional clearance between the pads and the synchromesh sliding coupler.

Safety locking of the gearbox selector
The system comprises two cylindrical locks of different lengths.
- short locking pin: selector rail 1st - 2nd
- long locking pin: selector rail 3rd - 4th
Their extremities are spherical and one of them has an extended lug. Each selector rail is machined both to lodge and to allow movement of the locks.

Operating principle
Example: Ratio 1 engaged - Hare range
When the selector rail is moved to select 1st gear, it forces its lock to move out of its lodging place and to lock the range selector rail in the "Hare" position. At the same time, this lock pushes another lock that in turn locks the 3rd - 4th selector rail, thus prohibiting any undue movement that might block the gearbox. The same reasoning applies to the Tortoise range and other gear ratios.


Parts list
(1) Selector rail 3rd - 4th (2) Short locking pin 1st - 2nd (3) Hare / Tortoise selector rail (4) Selector rail 1st - 2nd (5) Long locking pin 3rd - 4th (6) Gearbox housing (7) Selector 1st - 2nd (8) Reverse shuttle selector (9) Reverse shuttle selector rail (10) Locking pin (11) Spring (12) Plug
(13) Input unit housing (14) Reverse shuttle fork (15) Fork 1st - 2nd (16) Fork 3rd - 4th (17) Hare / Tortoise fork (18) Long spacer (19) Short spacer (20) Bolt (21) Pin



Disassembling and reassembling selector rails and adjusting forks and gearbox selector

Uncouple the tractor between the gearbox and the intermediate housing.
Remove the selector cover.
On tractors fitted with a creeper gearbox, the reducer unit located on the rear face of the gearbox does not hinder disassembly or reassembly of the selector.
Remove the bolts (20) from the selector (7) and forks (15) (16).
To carry out operations on the 1st - 2nd fork, use a short Allen key due to the limited space between the fork and the housing.
Disassemble the index assemblies (10) (11) (12) (18).
Push selector rail (4) towards the front and remove lock (2). Proceed in the same way for selector rail (1) and locking pin (5).
Take out selector rails (1) (4) through the rear of the gearbox.
Using a suitable pin punch, drive out pin (21) from the Hare / Tortoise fork (17) (Fig. 2).
Take out selector rail (3) through the rear of the housing.
Remove the 3rd - 4th (16) and the Hare / Tortoise forks.
The 1st - 2nd fork (15) cannot be removed from the housing unless the main shaft has previously been removed.
Clean and inspect the components. Replace any defective parts.
Install the selector rails, forks and selectors in the reverse order of disassembly.
During refitting, pin (21) on the Hare / Tortoise fork must be replaced
- The short locking pin (2) locks selector rail 1st - 2nd.
- The long locking pin (5) locks selector rail 3rd - 4th.
- The index assembly (10) (11) (12) (18) places selector rail 1st -2nd.
- The index assembly (10) (11) (12) (19) places selector rail 3rd - 4th.
Adjust forks and selector (7) (see below).

Adjustment
The positioning of forks (15) (16) and selector (7) is obtained via the difference between the distance between the centre of threaded holes "Y" and mark "Z" on the selector rails (1) (4) (Fig. 1). A different forward or rearward movement of the forks is obtained by acting on bolt (20) as required. The adjustment of forks is carried out with the gear engaged.
Smear the plugs of the indexing assemblies (10) (11) (12) (18) with Loctite 542 or equivalent and tighten. Lock fork (15) in 1st. Maintain the synchromesh sliding coupler against the pinion. Check that the rear pads are not in contact with the synchromesh sliding coupler by slightly moving the selector rail without moving the sliding coupler itself.
Repeat the operation (fork locked in 2nd), checking that the rear pads are not in contact with the synchromesh sliding coupler, by using the same method as in operation 13. Where necessary, adjust the fork using bolt (20) previously smeared with Loctite 221 or equivalent.
Proceed in the same way to adjust fork (16).

Tightening torques
- Bolt (20): 35 Nm without modifying its adjustment, Loctite 221.
- Plug (12): 50 - 70 Nm, Loctite 542.
Next, adjust selector (7) in line with the selector incorporated in fork (16).
Adjust the "S" Hare / Tortoise selector.
Install the selector cover. With the gear lever in neutral, check that locks (2) (5) are free in the rear bearing in the Hare / Tortoise range.
Couple the tractor between the gearbox and the intermediate housing.
Road test. Check:
- gear changing
- correct operation of the Hare / Tortoise range.
Check oil tightness of the gearbox and intermediate housing mating faces, selector cover and hydraulic unions.

Disassembling and reassembling selector rail and adjusting input unit fork

Uncouple the tractor between the engine and the gearbox.
Remove the input unit.
Disassemble the indexing assembly (10) (11) (12).
Remove bolt (20) from the reverse shuttle fork (14).
Take out selector rail (9) and fork.
Clean and inspect the components. Replace any defective parts.
Install the fork and selector rail.
Carry out the adjustment of the fork.

Adjustment


The positioning of fork (14) is obtained by the difference between the distance between "Y" and mark "Z" on the selector rails (9) (Fig. 4). A different forward or rearward movement of the forks is obtained by acting on the forward bolt (20) or the rear bolt, as required.
Install the locking stud (10), spring (11) and plug (12) tightened to 50 - 70 Nm and previously smeared with Loctite 542 or equivalent. Fit bolt (20) smeared with Loctite 221 or equivalent.
Position the fork, locked at the front. Maintain the synchromesh sliding coupler in thrust against the pinion. Pre-adjust the fork in accordance with the above principle.
Check that the front pads are not pinched against the synchromesh sliding coupler.
Repeat the operation (fork locked at the rear). Check that the rear pads are not pinched against the synchromesh sliding coupler.

The adjustment is correct when the space is identical between the pads located on either side of the fork and the synchromesh sliding coupler, when in the forward and reverse positions.
Alternatively and progressively tighten bolt (20) to 35 Nm without modifying its adjustment.
Install the input unit.
Couple the tractor between the engine and the gearbox.
Carry out a road test, checking for the correct operation of the mechanical reverse shuttle .
Check for the oil tightness of the selector cover and hydraulic unions.