Power Shuttle GBA20 gearbox – Speedshift

The Speedshift unit is located between the Power Shuttle reverse clutch and the mechanical unit comprising the driving gear. This is a hydraulically controlled gear shift mechanism providing two input ratios to the gearbox. This function is provided by:
- a multidisc hydraulic clutch;
- an epicyclic gear train consisting of a planet carrier with three double planet gears, an input sun gear and an output sun gear;
- a planet carrier hydraulic braking system.
The design of the Speedshift allows ratio shifting while driving without declutching, even at full load.

Specific feature of the epicyclic gear train assembly
Legislation in force in certain countries limits forward speed to 30 kph. In this case, the sun gears (6) and (7) and planet gears (12) of the Speedshift epicyclic gear train should be positioned as in figures.

Parts list 
(1) Seals (2) Rivets (3) Screw (4) Ring (5) Secondary shaft (6) Input sun gear (30 kph) Output sun gear (40 kph) (7) Input sun gear (40 kph) Output sun gear (30 kph) (8) Planet gear pins (9) Planet carrier unit (10) Friction washer (11) Rivet (12) Double planet gears (13) Housing (14) Spacers
(15) Hub (16) Needle roller bearing (17) Friction washers (18) Spring washer (Belleville) (19) Ring restrictor (20) Thrust plate (21) Brake disc (22) "O" ring (23) "O" ring (24) Screw (25) Hydraulic cover plate (26) "O" ring (27) Front cover plate (28) Clutch piston (29) "O" ring (30) Intermediate plates (31) Rings (32) Needle roller bearing (33) Ring carrier (34) Screw
(36) Primary shaft (37) Circlip (38) Tab washer (39) Washer (40) Ball bearing (41) Screw (42) Discs (43) Spring washers (48) Brake piston (50) Planet carrier assembly

Mechanical action - boosting
In this position, the hydraulic components are not supplied and the Speedshift operates in a mechanical manner. The oil in the chamber of pistons (28) and (48) returns to the housing via channel "C" and the solenoid valve mounted on the Power Shuttle clutch unit. This clutch unit is located on the front right-hand side of the gearbox. 

As the oil pressure has dropped, the planet carrier assembly (50) is locked in rotation by the Belleville washer (18) which compresses the thrust plate (20) and immobilises the disc (21) splined with the planet carrier assembly. Drive from the primary shaft (36) is transferred to the input sun gear (7) splined to the shaft. The sun gear (7) drives the double planet gears (12) idle-mounted on the pins (8). The planet gears in turn drive the output sun gear (6) firmly attached to the secondary shaft (5), ratio 1.26.

Hydraulic action: direct drive reduction
The range shifting is carried out via a pulse button integrated into the transmission lever handle. This button activates the solenoid valve mounted on the Power Shuttle clutch unit located on the front right-hand side of the gearbox. The solenoid valve simultaneously supplies the chamber of pistons (48) and (28). The brake piston (48) then presses against the thrust plate (20) which compresses the Belleville washer (18) thus releasing disc (21) and the planet carrier assembly (50). 

At the same time, the clutch piston (28) joins the intermediate plates (30) and the discs (42) driven by the hub (15). As the intermediate plates are firmly secured to the planet carrier with three lugs, drive is transferred from the input shaft (36) to the hub (15) and to the clutch assembly which drives the planet carrier (50). The primary shaft (36), the planet carrier assembly and the sun gears turn at the same speed as the secondary shaft (5), thus ensuring direct drive, ratio 1.
Disconnect the tractor between the engine and the gearbox. Drain the gearbox and the rear axle. Remove the spacer. Remove the Power Shuttle forward clutch. Remove the input unit. Separate the Power Shuttle reverse clutch from the input unit. Position the unit vertically.

Removing and disassembling the front cover plate

Remove the screws (24). Using two tabs or two makeshift rings, remove the shaft (36), the ring carrier (33) and the front cover plate (27) assembly.

Recover and discard the seals (1). Remove and discard the seal rings (31).

Remove the circlip (37). Remove the tab washer (38) and washer (39).
Separate the shaft (36) from the ring carrier (33).

If necessary, remove screws (34) (41). Separate and remove the ring carrier (33) from the cover plate. Remove the piston (48) by lightly tapping the cover plate with a wooden block or using a jet of compressed air.

Remove the seals (22) and (23) and discard them. The ring restrictor (19) is held in the cover plate by Loctite 648 or an equivalent product. The rivets (2) and (11) ensure oil channel tightness.