GBA20 gearbox - Super creeper unit


The super creeper reducing unit is located at the rear of the main gearbox. It is fitted as an option. It comprises:
- an input epicyclic gear train fitted with three planet gears
- an output epicyclic gear train fitted with five planet gears.
Each epicyclic gear train (input and output) consists of a sun gear/planet carrier/ring gear assembly.
Each ring gear is machined in a single unit.


Parts list 
(1) Input planet carrier (2) Friction washer (3) Cover plate (4) Output planet carrier (5) Screw (6) M8 screw (7) Circlip (8) Coupler (9) Input planet gears (10) Needle rollers (11) Output planet gears (12) Pins
(13) Input planet gear plates (14) Sun gear (15) Stop plate (16) Input epicyclic gear train (17) Output epicyclic gear train (18) Folded friction washer (19) Ring gear unit (20) Dowels (21) Link shaft
(22) Output planet gear plates (44) GBA20 gearbox output shaft



Kinematics and operation

Kinematics of the input epicyclic gear train (16) 
- Ring gear unit (19) blocked.
- Drive input via output shaft (44) of the GBA20 gearbox.
- Drive output via planet carrier (1).


Kinematics of the output epicyclic gear train (17) 
- Ring gear unit (19) blocked.
- Drive continuity via sun gear (14).
- Drive output to rear axle via planet carrier (4). The sun gear (14) is secured by splines on the planet carrier (1).

Operation 


The coupler (8) is secured by splines on the link shaft (21). Movement of lever A to Snail position moves the coupler (8) forwards and engages it with the planet carrier (4) via its external teeth. The speed of the link shaft (21) is 1/14 that of the gearbox output shaft (44). When the coupler (8) is engaged in the output planet carrier (4), the needle roller bearing (1) allows the link shaft (21) to turn at a different speed to that of the output shaft (44). When the super creeper range is selected, the Snail indicator light on the instrument panel comes on. The electrical signal corresponding to selection of the super creeper range is transmitted via switch C, which is fitted on the control unit


In normal gears, the gearbox output shaft (44) is engaged with the link shaft (21) when the coupler (8) is moved backwards, thus ensuring direct drive.



 Removing / install and disassembling / reassembling the epicyclic gear trains

Split the tractor between the gearbox and the rear axle.


Remove:
- the counter-nut (26)
- the adjustable lock (27)
- the fork (28) and the coupler (8).
Remove the screws (5).
Separate the super creeper unit from the gearbox. Place it on a workbench.
Remove the M8 screws (6).
Remove:
- the cover plate (3)
- the output planet carrier (4)
- the sun gear (14)
- the input planet carrier (1).
Recover the folded friction washer (18).
Separate the stop plate (15) from the ring gear unit (19). The dowels (20) are force fitted onto the ring gear unit (19).
Check and clean all components. Replace those that are defective.
Check that all dowels (20) are present on the ring gear unit (19).
Assemble the stop plate (15) on the ring gear unit.
Lightly smear the folded friction washer (18) with miscible grease. Position the folds of the friction washer face-to-face with the notches. Install the friction washer up against the input planet carrier (1).
Install:
- the input planet carrier (1)
- the sun gear (14)
- the output planet carrier (4)
- the cover plate (3).
Install and tighten the M8 screws (6) to a torque of 25 - 35 Nm.
Assemble the super creeper unit on the gearbox.
Install and tighten the screws (5) to a torque of 33.8 - 51.5 Nm.
Install:
- the fork (28) and the coupler (8)
- the adjustable lock (27)
- the counter-nut (26).
Adjust the fork locking mechanism (27).
Reconnect the tractor between the gearbox and the rear axle.

Disassembling and reassembling the planet carriers

Disassembling the input planet carrier
Position the input planet carrier (1) under a press and on top of a plate pierced with a hole to allow removal of the pins (12).
Drive out a pin using the press and a makeshift drift (Ø 12 mm) in the direction of the arrows.
The pin is force fitted into part E of the planet carrier.


Remove the planet gear (9) and plates (13) from the planet carrier. Recover the needle rollers (10).
Repeat operations to disassemble the other two planet gears.

Reassembling the input planet carrier
Clean and check all components. Replace those that are defective.

Preparing a planet gear 


Lightly smear the bore of the planet gear (9) with miscible grease.
Arrange the needle rollers (10) on the grease cartridge, taking care not to omit any.
Repeat to prepare the other two planet gears.

Install a planet gear pin
Place the input planet carrier (1) on a press.
Slide a planet gear (9), fitted with its needle rollers (10) and plates, (13) into the planet carrier.
Line up the planet gear and plates with the planet carrier pin hole (12).
Check that the axial channel and radial hole of the pin are not blocked.
Turn the axial channel inlet of the pin (12) as shown in figure.


Slide the pin partly into:
- the input planet carrier (1)
- the planet gear (9)
- the plates (13).
Turn the pin. Turn the radial hole R as shown.
Install the pin (12) so that its blunt end is almost level with surface F of the planet carrier.


Check manually on the planet gear (9):
- the presence of slight axial clearance
- the free rotation of the planet gear.
Repeat operations to fit the other two pins.

Disassembling the output planet carrier
Position the output planet carrier (4) under a press and on top of a plate pierced with a hole to allow
removal of the pins (12).
Drive out a pin using the press and a makeshift drift (Ø 12 mm) in the direction of the arrows.
The pin is force fitted into part E of the planet carrier.


Remove the planet gear (11) and plates (22) from the planet carrier.
Recover the needle rollers (10).
Repeat to disassemble the other four planet gears.

Reassembling the output planet carrier
Clean and check all components. Replace those that are defective.

Preparing a planet gear 


Lightly smear the bore of the planet gear (11) with miscible grease.
Arrange the needle rollers (10) on the grease cartridge, taking care not to omit any.
Repeat steps to prepare the other four planet gears.

Install a planet gear pin

Place the output planet carrier (4) under a press.
Install the friction washer (2) into the base of the planet carrier (4).
Slide a planet gear (11), fitted with its needle rollers (10) and plates (22), into the planet carrier.
Line up the planet gear and plates with the planet carrier pin hole (12).
Check that the axial channel and radial hole of the pin are not blocked.
Turn the axial channel inlet of the pin (12) as shown.
Slide the pin partly into:
- the output planet carrier (4)
- the planet gear (11)
- the plates (22).
Turn the pin. Turn the radial hole R as shown in pic.
Install the pin (12) so that its blunt end is almost level with surface of the planet carrier.
Check manually on the planet gear (11):
- the presence of slight axial clearance
- the free rotation of the planet gear. Repeat to fit the other four pins.

Adjusting the control

Cab side 


Place control lever A in the Snail position. The control lever may be located in two positions on the right-hand console, depending on whether or not an auto-hitch is fitted.
Screw the clevis (1) level with the end of the threaded part of the cable.
Install the clevis (1) onto lever A with the clip (7). Tighten the nut.
Screw the nut (3) onto the sheath end (5).
Install the sheath end and the lock washer onto the support. Tighten the nut (4). After tightening, check that the cable is not pinched.

Gearbox side


Place rod "B" in the "super creeper" position (Snail position, with the reducer dog (8) engaged towards the front, fork locked).
Screw the clevis (9) level with the end of the threaded part of the cable (6).
Install the clevis (9) to rod B using the clip (10). Tighten the nut (11).
Adjust the stop (12) with the nut (13), making sure that rod B is still firmly locked.
Tighten the nut (14). After tightening, check that the cable is not pinched.
Check that the control is locked in the "direct drive" position.