Dyna VT - Disassembling and reassembling the pumps


The steering pump is fitted at the end of the variable displacement pump. It is a 19cc fixed displacement pump, with a 120 bar maximum pressure and a gear ratio of 67/58. It is fitted to the variable displacement pump by two CHC M8 screws. It rotates around a coupling sleeve. The variable displacement pump has maximum capacity of 60cc, and a 400 bar maximum pressure.
The gear ratio is 67/58. Drive is transmitted directly to the gearbox by a gear train. The pump is fitted to the gearbox housing by two HM 12 screws.
The lubricating pump is a fixed displacement pump. It is a gear pump and is fitted to the same drive pinion as the service pump. It’s capacity is 23.4cc.


Diagram of the variable displacement pump and steering pump 



Disassembling the steering pump and the variable displacement pump

Exploded view of the variable displacement pump 

Part list 
1 - O’ring, 2 – Flange, 3 – Screw, 4 – Hose, 5 – Gasket, 6 – Plug, 7 - O’ring, 8 – Washer, 9 - Rigid pipe,10 – Screw, 11 - O’ring, 12 – Union, 13 - Rigid pipe, 14 - O’ring,15 – Union,16 - O’ring,17 - Elbow union,
18 – Hose,19 – Screw, 20 – Flange, 21 - O’ring, 22 – Collar, 23 – Hose, 24 - O’ring, 25 – Screw, 26 - Washer

Exploded view of the steering pump 

Part list 
27 – Screw, 28 - Union plate, 29 – Hose, 30 – Union, 31 – Screw, 32 - O’ring, 33 – Hose, 34 – Union, 35 - O’ring, 36 - O’ring, 37 – Union, 38 – Strainer,39 – Seal,40 – Union,41 – Seal,42 – Union, 43 - Rigid pipe, 44 – Union, 45 - O’ring, 46 – Washer, 47 – Screw, 48 - O’ring, 49 – Union, 50 – Hose


Chock the tractor and take off the rear right-hand wheel. Remove the exhaust system. Take off the right-hand protective guards. Take off the protective guard over the right-hand footstep. Remove the right-hand footstep.
Drain and remove the fuel tank. Drain the hydraulic oil. Remove the protective housings that might obstruct access. Disconnect the hydraulic pipes connected to the tank. Disconnect the hose (33) from the steering pump priority block.
Take out the attachment screws (10) from the hydraulic pressure pipe of the variable displacement pump. Take out the tank attachment screws.
Remove the oil tank. Take out the rigid pipe (9) through the port, then disassemble it. Remove the hose (50) from the steering pump priority block.
Take out the attachment screws (27) from the union plate (28).
Gently remove the plate from the spacer, and disassemble the hydraulic union from the priority block. Remove the “Load Sensing” control pipe from the variable displacement pump. Disconnect the hose (33) from the steering pump priority block. Loosen the collar (22), then disconnect the variable displacement pump suction hose (23). Take off the rigid pipe (43) fitted with its strainer (38). Access to the union is limited, so a 41 mm pipe wrench is recommended. Remove the union (44) from the pump. Take out the attachment screws (47) from the steering pump. Remove the steering pump.
Discard the O’ring. Remove the coupling sleeve. Loosen and take out the screws (3), then remove the pressure union of the variable displacement
pump. Access is limited, so a 10 mm multipurpose wrench is recommended.
Remove the return rigid pipe (13) to the variable displacement pump tank. Access is limited, so a 27 mm pipe wrench is recommended. Remove the screws (25) from the variable displacement pump flange. Access is limited, so an 18 mm offset pipe socket is recommended. Support the variable displacement pump across the housing with a wooden shim, and pull the pump away of the gear teeth. Take the pump out of the spacer;
Discard the paper gasket. It is recommended to turn the suction channel of the pump upwards and to remove an attachment stud from the tank to extract the pump more easily.

Reassembling the steering pump and the variable displacement pump

Grease and fit new seals. Screw two M12 guide studs into M12 screw holes to assist pump assembly. Insert the variable displacement pump into the spacer and slide it onto the studs. A wooden shim can be fitted to assist pump positioning. Take out the guide studs and attach the pump using the two M12 attachment screws (25). Tighten the M12 screws (25) to a torque of: 86Nm
Fit the return rigid pipe (13) to the variable displacement pump tank. Access is limited, so a 27 mm pipe wrench is recommended. Fit the variable displacement pump pressure hose (4). Tighten the screws (3) to a torque of: 50Nm. Fit the coupling sleeve of the two pumps.
Fit a new O’ring on the steering pump centring diameter, and fit the steering pump in its housing. Fit and tighten the steering pump screws (47) to a torque of: 25Nm. Fit the steering pump union (44). Fit the steering pump rigid pipe (43) fitted with its strainer (38). Connect the hose (23) on the variable displacement pump suction channel, and tighten the collar (22). Attach the hose (33) on the steering pump priority block. Fit the elbow (17) on the variable displacement pump. Fit the steering pump priority block hose (50) and tighten the three screws (27) to a torque of: 10Nm.
Fit the hose (50) on the steering pump priority block. Take out the pressure hose (4) from the variable displacement pump through the spacer plug (6), and connect it to the rigid pipe (9) of the washer (8). Refit the stud if removed when extractng the pump. Clean the mating faces of the tank and spacer. Smear one of the cleaned surfaces with sealing product (ref. X903.050.074). Fit the hydraulic tank. Fit and tighten the tank attachment screws. Tighten the screws (10) of the washer (8). Fit the hose to the union (30). Fit the tank hydraulic channels. Refit the protective housings that were removed. Refit the fuel tank. Refit the footstep. Refit the protective guard over the right-hand footstep. Refit the right-hand protective guards.
Refit the exhaust system. Top up the hydraulic oil (approximately 65L). Check the operation and tightness of the hydraulic circuit. Repair any defective elements or seals. Refit the rear right-hand wheel.

Exploded view of the service pump (18 bar)

51 – Screw, 52 - Rigid pipe, 53 – Union, 54 – Screw, 55 – Union, 56 - O’ring, 57 - O’ring, 58 – Screw, 59 - O’ring, 60 – Cover, 61 – Catchdog, 62 - O’ring, 63 - Hydraulic pump, 64 - O’ring, 65 – Insert, 66 – Screw, 67 – Screw


Disassembling the lubricating pump

Exploded view of the lubricating pump 

Part list 
68 – Key, 69 – Washer, 70 – Screw, 71 – Screw, 72 - O’ring, 73 - O’ring, 74 – Filter, 75 – Screw, 76 – Cover, 77 - Suction filter, 78 - O’ring, 79 – Circlip, 80 – Pipe, 81 - O’ring, 82 – Pump, 83 - Drive pinion, 84 – Circlip


Remove the transmission unit. Take out the screws (75), then remove the cover (76). Remove the filter (74). Loosen the pipe on the pressure filter side.
Loosen the pipe on the rear axle side. Remove the circlip (79) from the suction pipe. Fit home the suction pipe in the suction filter pipe to release it from the pump. Loosen and remove the 2 screws (71). Remove the lubricating pump.
Remove the suction pipe. Discard the O’rings. Take off the pump pinion circlip (84). Remove the pump pinion (83). Take off the key (68).
Check the pump condition, and replace it if required.

Reassembling the lubricating pump

Fit the key (68) in its housing. Fit the drive pinion (83). Fit the shaft circlip (84). Fit the pump in its housing in the gearbox. Hold it in position using 2 screws. Refit the pipe on the pressure filter side and rear axle side.
Prepare the suction pipe. Fit the 2 O’rings (81) and circlips (79). Fit the side not fitted with the O’ring in the suction filter pipe (77). Smear the O'ring with miscible grease and fit home the pipe in the suction pump. The circlip groove on the suction filter pipe side must be cleared. Smear it with miscible grease, then slide the O’ring into its groove. Fit the circlip in its groove. Fit the pipe into the suction filter until it abuts against the circlip. Fit the circlip on the pipe, on the pump side. Definitively tighten the pump attachment screws to a torque of: 25 Nm. Fit the suction filter (74). Fit the cover (76) using the 3 screws (75). Tighten the screws (75) to a torque of:25Nm.  Refit the transmission unit.