GBA20 gearbox - Intermediate Shaft


The intermediate shaft and its gears form the upper shaftline of the GBA20 gearbox with mechanical reverse shuttle. It supports the 1st to 4th driven gears. The shaft rear teeth (54) are constantly meshed with the Tortoise gear. The shaft is supported by:
- the tapered roller bearing (63) and (64) housed in the rear bearing of the input unit;
- the tapered roller bearing (52) and (53) located in the rear bearing of the gearbox.
The four gears are held in position by the spacers (57) and (82). The operating clearance for these gears is obtained by inserting the shims (58) between the 1st (60) and 2nd (59) driven gears.


Parts list 
(50) Oil deflector (51) Shim(s) (52) Bearing cup (53) Bearing cone (54) Shaft (55) 3rd driven gear (56) 4th driven gear (57) Spacer (58) Shim(s) (59) 2nd driven gear (60) 1st driven gear (61) Circlip (62) Needle roller bearing (63) Bearing cone (64) Bearing cup (82) Spacer

To correctly shim the intermediate shaft tapered roller bearings, it is necessary to remove the gearbox.


Split the tractor between the gearbox and the rear axle. Split the gearbox from the engine. Place the gearbox on a workbench or a suitable support. Remove the selector cover plate. Remove the input unit.
After removing the input unit, pair the bearing cup housed in the input unit rear bearing with the intermediate shaft front bearing cone.

Removing and install the shaft and gear assembly

Remove the oil deflector (50) using a slide hammer puller and remove the shims (51) and the cup (52) to release the rear end of the shaft.
Take the shaft and gear assembly out through the front of the housing, by tilting it so that the gears are released from the lower shafts. When removing the shaft, do not insert the handling bar in the bore as this will damage the needle roller bearing (62). If necessary, carry out the operation with the help of an assistant.
Clean and check all components. Replace those that are defective.
In the housing, position the assembled shaft with its related gears.
If necessary, check and correct the shimming of the shaft. Otherwise, refit the cup (52), the original shims and the oil deflector (50).

Removing and install the gears

Extract the bearing cone (63).
Remove circlip (61) by opening it up as little as possible.
Remove 2nd gear (59), shims (58), 1st gear (60) and spacer (57).
Remove 4th gear (56), spacer (82) and 3rd gear (55).
Clean and check all components. Replace those that are defective.
Install the 3rd gear (55), spacer (82) and 4th gear (56).
Install the spacer (57). Fit the 1st gear (60) and the 2nd gear (59), temporarily without the shims (58).
Install the circlip (61).
Shim the gears.
Install the shaft, assembled with its related gears, in the housing.

Replacing the tapered roller bearings of the intermediate shaft

Remove the shaft (54) and gear assembly.
Extract the bearing cones (53) and (63). Discard them.
If necessary, replace the shaft.
If the shaft (54) has been replaced: Using a suitable fixture and a press, fit a new needle roller bearing (62) thrust up against the shoulder of the shaft. Check needle rotation after assembly.
Reassemble the gears.
Install bearing cones (63) and (53) using a press and a suitable fixture.
Position the shaft, assembled with its related gears, into the housing.
Shim the shaft.

Shimming the gears

The gears should be stacked temporarily without the shims (58).
Using a set of shims, measure the space between the 1st gear (60) and the 2nd gear (59).
Depending on the measured distance, choose shim(s) of an appropriate thickness to obtain the clearance J1 = 0 to 0.25 mm.


Remove the circlip (61), opening it up as little as possible, and remove the gear (59).
Slide the previously selected final shims onto the shaft. Refit the gear and position the circlip correctly.
Install bearing cone (63).
Install the shaft, assembled with its related gears, in the housing.

Shimming the shaft

To carry out shimming on the intermediate shaft, the input unit must be refitted.
Carry out the shimming on the shaft to obtain a clearance of J2 = 0 to 0.08 mm.


Install the makeshift tool in the shaft.


Slightly compress the spring, while tightening the nut of the tool, to correctly seat the bearing cones in their cups.
Rotate the shaft a few turns. Check spring compression again.
Using a depth gauge, measure dimension X between face A of the bearing cup (52) and face B of the housing.
Measure the thickness Y of the oil deflector (50).
Calculate the difference between X and Y.

Determine the thickness of shims required to obtain the clearance J2. If possible, shim to the minimum tolerance.
Remove the compression tool.
Install the oil deflector in the housing.
Install the input unit.
Install the selector cover plate.
Attach a sling to the gearbox. Lower it from the workbench or suitable support.
Reconnect the gearbox and the engine.
Reconnect the tractor between the gearbox and the rear axle.
Check:
- tightness of the hydraulic systems;
- correct operation of electrical circuits.
Carry out a road test of all controls.
Check the tightness of the unions and mating faces (selector cover plate, gearbox on rear axle).