GBA20 gearbox - Power Shuttle control unit

The unit (1) fixed to the right-hand side and front of the gearbox carries out two hydraulic functions quite separate to the input unit. It controls:
- the power shuttle,
- the Dynashift.

The channels and ducts machined in the unit allow oil under pressure to be directed to the reverse shuttle proportional solenoid valves and the Dynashift solenoid valves EV1 and EV2. All solenoid valves are controlled respectively by the tractor electronic system. A 60 micron filter element (8) is located under the right-hand hydraulic cover, upstream from the control unit. This additional filter supplies clean oil to the spool of each solenoid valve.

Presentation of control unit and hydraulic lines

Parts list 
(1) Control unit (2) Return to reverse clutch housing (3) Return to forward clutch housing (4) Reverse shuttle: 17 bar supply line to forward clutch (5) 

Reverse shuttle: 17 bar supply line to reverse clutch (6) Accumulator (Nitrogen) (7) Main 17 bar supply line (8) 60 micron filter element
(9) Dynashift: to internal forward clutch line (17 bar) (10) Dynashift: to internal reverse clutch line (17 bar)

Control of the Power Shuttle

Identification of ports on control unit

(1) Control unit (2) Return to reverse clutch housing (3) Return to forward clutch housing (4) Pressure outlet to forward clutch (5) Pressure outlet to reverse clutch (7) Control unit main supply (17 bar) (13) Control unit pressure connector (14) Reverse clutch pressure connector (15) Forward clutch pressure connector

Each of the hydraulic return lines of the proportional solenoid valves (11) and (12) has separate channels. This design avoids any back pressure from one solenoid valve to another.

Proportional solenoid valve

Remove flange (1).
Drive off the solenoid valve (11) or (12) by gently applying pressure with a screwdriver between the valve and the unit.

Check the condition and cleanliness of the O’rings fitted on the solenoid valve.
Position and manually drive the solenoid valve into its housing, beyond the point of resistance (O’rings squeezing).
Position the flange. Tighten the screw from 8 to 11 Nm.

Identification of ports on a proportional solenoid valve 

A: Clutch supply ports
B: Clutch return ports
P: 17 bar pressure

Electrical connection 
C: Solenoid supply

Dynashift control

Identification of ports on control unit 
(1) Control unit (9) Pressure outlet to forward clutch (10) Pressure outlet to reverse clutch (16) Forward clutch pressure connector (17) Reverse clutch pressure connector

In the control unit, the Dynashift part includes two internal channels A and B which allow oil to circulate from one solenoid valve to the other. The four Dynashift ratios are managed by two solenoid valves.

 Characteristics of the solenoid valves

 Identification of ports 

C: To port F
D: Non-return valve
E: Port to front piston
F: Port to rear piston
P: 17 bar pressure
R Return

The removal and install procedure for solenoid valves EV1 and EV2 is the same as that for a proportional solenoid valve.

Explanation of Dynashift ratios

Ratio A 

Ratio A is obtained when solenoid valve EV1 is supplied. Oil under pressure can also reach channel A.
Channel A directs the oil to the front piston via port E and to solenoid valve EV2. As this is in neutral position, the oil can pass through the spool and port F to the chamber of the rear piston. The two pistons are therefore under pressure.

Ratio B 

Ratio B is obtained when the two solenoid valves are supplied. Therefore the flow of oil to the rear piston is interrupted. The rear piston is pushed out by springs which send the oil into channel B. This channel is
joined to the housing by solenoid valve EV1.

Ratio C 

Ratio C is obtained by switching off solenoid valve EV1, while maintaining solenoid valve EV2 under voltage. Channel A is no longer pressurised but is connected to the housing. As a result, the front piston
can return to neutral position. Channel B is under pressure. The oil flows to the rear piston via solenoid valve EV2.

Ratio D 

Ratio D is obtained by switching off EV2. The two solenoid valves are at rest. The two pistons are connected to the housing via channel A.

Removing and install the control unit

Mark and disconnect the connectors on solenoid valves EV1 and EV2 of the Dynashift as well as those of the proportional solenoid valves (12) (11) of the power shuttle forward and reverse clutches.
Disconnect and remove pipes (2), (3), (4), (5), (7) and (9). To prevent oil flowing from the gearbox, it is advised to disconnect the return pipes (2) and (3) at their higher connections.

Unscrew the support (1) from the gearbox. Remove the “support and unit” assembly by gradually unscrewing the union (10) (Dynashift reverse clutch supply).

Install the “support and unit” assembly. Tighten:
- the screws fixing the support to the gearbox to 50 - 70 Nm,
- the screws fixing the unit to the support to 25 - 35 Nm.

Reconnect the pipes and connectors. If it was necessary to replace the control unit or proportional solenoid valves, test:
- the 17 bar pressure of the unit,
- the Dynashift clutch pressures,
- the pressure of the reverse shuttle forward and reverse clutches.
Special point
When pressurised, the reverse shuttle clutches must be calibrated using Wintest.

Carry out a road test of the hydraulic functions affected by the repair work.
Check the oil tightness of the hydraulic unions.