Rear axle - Trumpets with double reduction

Some tractors are fitted with trumpets containing two epicyclic gear trains, also known as double reduction. These drive units allow for a higher reduction ratio and lower tractor transmission torque. They are housed in a compartment and are comprised of the trumpet, two primary crownwheels (47) and two secondary crownwheels (15) and a spacer (48). The brake plate (30) partially closes the drive unit compartment.

Double reduction construction

The axle shaft is supported by two bearings comprising cups (8) (12) and bearing cones (7) (13) mounted in opposition to each other. The input shafts (31) are of different lengths ; the long shaft is fitted in the left hand side trumpet. The crownwheels, spacer and brake plate are positioned by pins (14). The pre-loading of the taper roller bearings is provided by shim(s) (26) placed at the end of the axle shaft. Shaft (2) and planetary carrier (25) are held by washer (27) and bolt (28). The oil tightness between the trumpet, crownwheels, spacer and brake plate is provided by silicone seals (Silicomet type). The cassette seal (3) protects the outer bearing comprising cup (8) and cone (7). The oil splash lubrication for the mechanical assemblies is provided by transmission oil coming from the shared oil tank formed by the intermediate housing and the centre housing. The centre housing is linked to the lower part of the trumpet by an external transfer pipe. The brake plate contains a port "O" allowing lubrication and cooling of the discs by a flow of oil coming from the booster circuit. The transmission oil within the trumpet is kept at the correct level via an oblique pipe (56). This pipe is located in the drive unit compartment and communicates with the external transfer pipe. The inner chamber of the trumpet is maintained at atmospheric pressure by a breather pipe screwed onto the left lift ram support. This breather pipe also ensures the venting of the shared oil tank. The input shaft (31) drives brake discs (35) via a splined hub (32) held by snap ring (33).

- In order to maintain an operational clearance between the planetary gears, the sun gears and crownwheels the secondary sun gear (51) floats on ball bearings (19) (49).


Primary epicyclic gear train
- The primary planetary carrier (24) is integral via splines with the secondary sun gear (51) and comprises three planetary gears (20) that engage with crownwheel (47) and primary sun gear (44) splined onto input shaft (31).

Secondary epicyclic gear train
- The secondary planetary carrier (25) integral via splines with axle shaft (2) possesses six planetary gears (18) in constant engagement with crownwheel (15) and secondary sun gear (51). It receives movement coming from the primary epicyclic gear train to then transmit it to axle shaft (2).

Parts list
(1) Bush (2) Straight shaft (3) Cassette seal (4) Thrust washer (5) Locating pin (6) Circlip (7) Bearing cone (8) Bearing cup (9) Washer (10) Trumpet (11) Nut (12) Bearing cup (13) Bearing cone (14) Pins (15) Secondary crownwheel (16) Tab washer (17) Stop ring (18) Secondary planetary gears
(19) Ball bearing (20) Primary planetary gears (21) Circlip (22) Roller bearing (23) Roller bearing (24) Primary planetary carrier (25) Secondary planetary carrier (26) Shim(s) (27) Lock washer (28) Bolt (29) Circlip (30) Brake plate (31) Input shaft (32) Splined hub (33) Snap ring (34) Studs (35) Brake discs
(36) Stud (37) Studs (38) Intermediary plate (39) Drilled stop pin (40) Bolt (41) Stop pin (42) Circlip (43) Magnetic drain plug (44) Primary sun gear (45) Circlip (46) Washer (47) Primary crownwheel (48) Spacer (49) Ball bearing (50) Washer (51) Secondary sun gear (52) O’ring (53) O’rings
(54) Transfer tube (55) Cup plug (56) Oblique pipe (57) Locating pin

Removing and  Install the trumpet assembly

Drain the centre housing and the oil trapped in the trumpet that is being removed.
- The drain plug (43) of the trumpet is located behind the transfer tube (54).

Immobilise the tractor. Take off the wheel. Place an axle stand beneath the centre housing.
Remove the bolt holding the cab and if necessary also take out bolt from the rear support above the trumpet.
If necessary, slightly raise the side of the cab and check that there is no interference with nearby elements. Chock the cab using a suitably adapted axle stand.
Remove bolts and the stabiliser support. Take off circlip and remove the lower pin of the lift ram. Using a strap, pull the ram away from the trumpet.
Position a suitable support beneath the trumpet.
Remove nuts (11) and washers (9) without taking out bolts (40).
- These bolts serve to hold the crownwheel, spacer and brake plate assembly on the trumpet.
Unstick and separate the trumpet assembly complete with the input shaft (31), brake plate (30), crownwheel (15) (17) and spacer (48) from the centre housing. Recover the brake discs (35), the intermediate plate (38) and the stop pins (39) (41).
- Brake piston ‘P’ remains in the housing (1).

Remove the transfer tube (54) and discard the O’rings (53).
- The studs (34) (36) (37), screwed into the centre housing are of different lengths. Before fitting, their threads must be lightly smeared with Loctite 270 or equivalent.
- Place the studs in the housing, respecting their length and location:
. (34): Ø 16 mm - L 363 mm
. (36): Ø 16 mm - L 378 mm
. (37): Ø 16 mm - L 388 mm

Clean the site of the silicone seal on brake plate (30) and the centre housing. Check that all previous traces of sealing compound have been removed. Properly dry the components.
Coat angle "D" of the centre housing (1) with a sealing compound (Silicomet type).

- The diameter of the bead (seal) must be uniform, small section and without joins.
Check that discs (35) slide normally on the hub (32). Check that the stop pins (39) (41) are free in:
- the drilled holes of piston"P" and the intermediate plate (38).
- the recesses of the brake plate (30) and the centre housing (1).
Check for the presence of locating pin (5) on the centre housing.
Check that port "O" on the brake plate (30) is not obstructed.
Check for the presence of the radial drilled holes on the intermediate plate (38).
On the trumpet, Install plate (38) by placing either side of it a brake disc (35) on hub (32) and position the stop pins (39) (41).
- The drilled pin is fitted in the upper recess of the brake plate.
Install new o’rings (53) smeared with miscible grease onto the transfer pipe (54). Introduce the pipe into the trumpet port.
With the help of a second operator and the support equipment used for removal, engage the trumpet on the studs. Turn the axle shaft and push the trumpet until it mates with the centre housing. Check that the end of the transfer tube (54) as well as the stop pins (39) (41) are correctly positioned in their respective grooves in the housing. Place washers (9). Install and tighten nuts (11) to a torque of 247 - 253 Nm. Remove the support from beneath the trumpet. Reinstall the lift ram. Replace the stabiliser support and tighten the bolts to 480 – 640 Nm.
Reinstall the various elements that surround the trumpet. Reinstall the wheel and tighten the nuts or studs to the correct torque depending on the version.

Tightening torque
- Cab fixing bolt (silent bloc): 200 - 260 Nm, Loctite 270 or equivalent.
Top up the oil level in the housings and check on the transparent tube located on the left-hand side of the centre housing.
Check the operation of the lift system. Carry out a road test of the brake circuit.
Check the oil tightness of:
- the trumpet
- the O’rings (53) located on transfer tube (54).