Speedshift - Mechanical reverse shuttle GBA20 gearbox



The Speedshift unit is mounted between the hydraulic mechanism of the engine clutch and the mechanical reverse shuttle. It is a hydraulically controlled gear shift system 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.
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 a pic.


Parts list 
(2) Screw (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) Seal (7 mm thick) (11) Seal (10 mm thick) (12) Double planet gears (13) Housing (14) Spacer (15) Hub (16) Needle roller bearing (17) Friction washers (18) Spring washer (Belleville) (19) Rivets (20) Thrust plate (21) Brake disc (22) "O" ring (23) "O" ring (24) "O" ring (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) Threaded plug Ø 8
(35) Threaded plug Ø 10 (36) Primary shaft (37) Circlip (38) Tab washer (39) Washer (40) Ball bearing (42) Discs (43) Spring washers (46) Seal (47) Seals (48) Brake piston (50) Planet carrier assembly (65) Needle roller bearing (66) Seal


Parts list 
(2) Screw (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) Seal (7 mm thick) (11) Seal (10 mm thick) (12) Double planet gears (13) Housing (14) Spacer (15) Hub (16) Needle roller bearing (17) Friction washers (18) Spring washer (Belleville) (19) Rivets
(20) Thrust plate (21) Brake disc (22) "O" ring (23) "O" ring (24) "O" ring (25) Hydraulic cover (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) Threaded plug Ø 8 (35) Threaded plug Ø 10 (36) Primary shaft
(37) Circlip (38) Tab washer (39) Washer (40) Ball bearing (42) Discs (43) Spring washers (46) Seal (47) Seals (48) Brake piston (50) Planet carrier assembly (65) Needle roller bearing (66) Seal

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 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 fitted at 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.