Robotic mechanical GBA25 gearbox - Adjusting the selector rails and forks


To carry out this adjustment, the primary and secondary shafts must be correctly supported and shimmed in the housing.


Parts list 
(L52) Range 1 control solenoid valve
(L53) Range 2 control solenoid valve
(L54) Range 3 control solenoid valve
(L55) Range 4 control solenoid valve
(L56) Range 1 switch
(L57) Range 2 switch
(L58) Range 3 switch
(L59) Range 4 switch

Preliminary operations
Install solenoid valves (L52), (L53), (L54) and (L55).
Fashion a union to supply the control circuit with compressed air at a maximum pressure of 4 barConnect the selector rail adjustment tool ref 3378805M1.

Using the selector rail adjustment tool ref 3378805M1


The selector rail adjustment tool is used to supply the solenoid valves (L52), (L53), (L54) and (L55) of the gear box, in order to carry out various adjustments. The range switches (L56), (L57), (L58) and (L59) can be checked once the selector rails have been adjusted and the switches fitted. Each LED on the tool corresponds to a switch. The switches on the tool supply the solenoid valves of the gear box. They work independently of the LED lighting. The range switches light the LEDs of the tool. When a range is engaged, the corresponding LED for the range is lit. The switches are normally closed. When a range is engaged, they open the circuit and the implement reverses the signal to light the LEDs. When the switches are not connected, the four LEDs on the tool are thus lit.

Connecting the tool


- Connect the tool to a 12V, 4A power supply.


- Connect the connectors (1) to the solenoid valves and the connectors (2) to the range switches. Each wire is marked with a number indicating the range concerned.


Switches, LEDs/connectors
Switch 1 - Solenoid valve L52
Switch 2 - Solenoid valve L53
Switch 3 - Solenoid valve L54
Switch 4 - Solenoid valve L55
Switch R - Solenoid valves L52, L53, L54 and L55
LED 1 - Switch L56
LED 2 - Switch L57
LED 3 - Switch L58
LED 4 - Switch L59

Using the tool
• Supplying the solenoid valves Activate switches 1, 2, 3 and 4 one by one, in order to supply the solenoid valves required to adjust the selector rails. To return the two selector rails to neutral automatically, use switch R on the implement (4 solenoid valves supplied).


For example:
Solenoid valve (L52) supplied by switch 1—the selector rail pushes switch (L56) and lights LED 1.
Checking the switches
Once the selector rails have been adjusted, fit the switches. Engage a range using the corresponding
switch. The LED that corresponds to the range engaged should light up.



Checking the selector rails before adjustment
Before adjusting the travel of the selector rails, it is important to check that their movement is within the
permitted tolerances.


Using a depth gauge and a suitable fixture, check the following dimensions (see the table):

- X1: distance between face F of the housing and the end of the selector rail with the range 1 or 3 engaged,

- Y : distance between face F of the housing and the end of the selector rail in neutral position,

- Z1: distance between face F of the housing and the end of the selector rail with the range 2 or 4 engaged.

X1 20.785 ± 1              21.830 ± 0.8
Y 32.215 ± 1.245        33.213 ± 1.093
Z1 43.625 ± 0.9           44.425 ± 0.8

If the measured dimensions are outside these tolerances, manually turn the gears using the reverse driving pinion, then repeat the measurements. If the dimensions are still incorrect, check that the selector rails and synchronisers have been fitted correctly.


 Adjusting the selector rails

Adjusting the selector rail (98) (ranges 1 and 2)
Set the rail (98) to neutral.
Install the castellated nut without tightening (109).
Engage range 2. (Supply L53).
Tighten the nut (109) up against the cover (6).
Reposition the selector rail to neutral. Screw on the nut (109) by two slots and line up the next slot
opposite the hole of the locking screw (107).


With paint, mark the position of the nut (109) in relation to the cover (6). The synchroniser may not fully engage when the gearbox is not running. If this is the case, position the shaft (121) and reverse transfer pinion (119) and slowly run the gearbox while engaging the range.
Install the castellated nut (108). Screw it on until it is almost touching the nut (109). Ensure the nut (109) stays in its set position and that the paint marks are not removed.
Install the plate (111). Install the screws (110) smeared with Loctite 242 or equivalent. Tighten to a torque of 29 - 37 Nm.

Engage range 1. (Supply L52) 
Unscrew the nut (108) fitted home against the cover (111).
Reposition the selector rail to neutral. Unscrew the nut (108) by two slots and line up the next slot opposite the hole of the locking screw (107).
With paint, mark the nut (108) aligned with the mark on the cover (6).
Insert the screw (107) to lock the nuts (108) and (109), aligning the marks made during operations.
Check for correct operation. The nuts should effectively act as a stop.
Firmly fit the screw (107), lightly smeared with Loctite 242 or equivalent. Tighten to a torque of 12 - 16 Nm. Adjusting selector rail (73) (ranges 3 and 4). Repeat operations with the selector rail (73) and nuts (99) and (101).

Adjusting the interlock mechanism

This adjustment must be carried out after setting the selector rails.
Screw home the rod (106) in the reverse pitch nut (131).
.Using the selector rail adjustment tool ref. 3378805M1, engage a range on a selector rail and leave the other selector rail in neutral.


Unscrew the rod (104) until the lock reaches maximum axial clearance as shown in:
J = 0.1 to 0.3 mm. Tighten the locknut (105).

Check
Using the selector rail adjustment tool ref. 3378805M1, engage a range on a selector rail. Try to shift a range on the other selector rail. It should not engage. Repeat the procedure with all the ranges.

Assembling the intermediate speed sensor


Install the sensor (C) lightly smeared with Loctite 577 or equivalent.
Screw the sensor home on the pinion (25) without forcing it, then unscrew by ¾ of a turn. Tighten the locknut to a torque of 5 - 7 Nm.
Install the gearbox on the rear axle and engine.
Reconnect the harnesses and hydraulic pipes that were removed.
Check the level of the transmission oil.
Carry out a gearbox calibration and check the transmission for correct operation.