GPA20 rear axle - Normal Duty trumpet housings

The trumpet housings support the right and left-hand axle shafts and contain the final drive units that transmit the rotation from the differential assembly. Both trumpet housings are symmetrical and fitted on either side of the centre housing.

The axle shaft (2) is supported by two opposing tapered roller bearings (5) (8). External sealing is ensured by a three-lipped seal (3) and internal sealing is provided by a single lip seal (7). The three-gear final drive unit (14) planet carrier assembly (10) is integral in rotation with the shaft (2) via splines. The Normal Duty trumpet housing planet gears have a single row of needle rollers (15). The internal faces of the planet carrier (10) are rough cast and therefore require adjustment using friction shims (13). Shims (25) placed at the end of the shaft are used to preload the tapered roller bearings. The shaft (2) and the planet carrier (10) are held in place by the washer (24) and the screw (23). The final drive ring gear (21) is force fitted into the trumpet housing and held in place by the three screws (16). It has three pins (20) ensuring centring of the brake plate (17). Differential rotation is transmitted to the planet gears of the final drive via a sun gear shaft (22) on the teeth of which the brake disc (18) is fitted. The brake discs are lubricated by a continuous flow of oil from the linkage valve.

Parts list
(1) Wheel stud (2) Axle shaft (3) Three-lipped seal (4) Seal cage (5) Bearing cup (5A) Bearing cone (6) Trumpet housing (7) Seal (8) Bearing cup (8A) Bearing cone (9) Tab washer (10) Planet carrier (11) Snap ring (12) Planet gear pin (13) Friction shim(s) (14) Planet gears (15) Needle rollers
(16) Screw (17) Brake plate (18) Brake disc (19) Screw (20) Pin (21) Final drive ring gear (22) Sun gear (23) Screw (24) Washer (25) Shim(s) (26) Pin (27) Plug

Trumpet housing assembly

Immobilise the tractor. Apply the hand brake. Chock between the frame and the front axle. Drain the rear axle.
Using a trolley jack, raise the relevant side of the tractor.
Place an axle stand in position. Remove the wheel.
Remove the stabilising support. Disconnect the hose (1) or (3) and the brake lubrication pipe(s)Remove cab screws A.

Raise the cab sufficiently to allow the trumpet housing to be removed (chock the cab). Check the gap between the bonnet and the windscreen (remove the body if necessary). If replacing the trumpet housing, remove the supports C by removing the screws B.
Underneath the trumpet housing, position a suitable support on a trolley jack.
For the left-hand trumpet housing, disconnect the supply hose from the linkage valve (plug the channels). Loosen the screws (19).

With the help of an operator and in compliance with the safety regulations, separate the trumpet housing from the rear axle housing.
- the brake disc (18)
- the sun gear (22)
- the centring pin (26)
Remove the brake plate (17).

Clean the mating faces on the housing and on the trumpet housing with a non-greasy solvent.
Apply a bead of silicon resistant to hydrocarbons (Silicomet type) to the inside edge of the housingCheck that the disc (18) slides freely on the sun gear (22).

Reinstall the centring pin (26), the sun gear (22) and the brake disc (18).
Screw two diametrically opposed guide studs onto the housing.
Reinstall the brake plate (17) in the trumpet housing. In order to hold the plate in place, apply three spots of miscible grease to the face of the ring gear (21).
Couple the trumpet housing to the rear axle, following the safety procedures used during its removal.  Turn the shaft (2) to engage the sun gear (22) in the planet gears.
Clean the screws (19) and smear them with Plastex, Hylomar or an equivalent sealing paste. Install and tighten the screws (19) to a torque of 170 - 210 Nm. Install the cab screws. Reinstall the other removed parts.
Top up the oil level in the rear axle.
Install the wheel. Tighten to a torque of 400 - 450 Nm.
Remove the axle stand. Test the linkage and the brake system.
Check tightness:
- between the trumpet housing and the rear axle housing
- of the linkage valve supply hose
- of the brake lubrication pipes.

Planet carrier

Remove the trumpet housing. Remove the screw (23).
Take off the retaining washer (24) and the shim(s) (25).
Remove the planet carrier (10).

Open the snap ring (11).
Using a hammer, tap gently on the three pins (12).
Take out the three pins (12) and the snap ring (11).
Remove the three planet gears (14), the needle rollers (15) and the shims (13).

Clean the planet carrier (10), the pins (12) and the planet gears (14). Check the parts.
Smear the needle rollers with miscible grease. Install a row of needle rollers in each planet gearShim the planet gears. The shims (13) are available in three different thicknesses.
Install the planet gears (14) with the shims (13) of medium thickness on either side of the planet gear. Engage the three pins (12).
Use a set of shims to determine a thickness of shims (13) to fit to obtain an axial clearance of between 0.15 and 0.55 mm on each planet gear.
Pull gently on the three pins, and Install the shims (13).
Push back the three pins and the snap ring (11). Open the snap ring (11).
Tap gently on the three pins so that the snap ring Install into the groove of the planet carrierEnsure that the tab washer (9) is present.
Reinstall the planet carrier. Install shims to obtain the required preload.
Reinstall the trumpet housing.

Bearings and seals

Remove the trumpet housing from the rear axle housing.
Remove the planet carrier. Remove:
- the tab washer (9)
- the cone (8A) (free fitted on the shaft).
Take the shaft (2) out of the trumpet housing.
Extract the cone (5A). Drive out the lip seal (3).
Using a puller, take out:
- the cup (5)
- the cage (4) of the seal (3)
- the cup (8)
Drive out the seal (7).

The ring gear (21) is force fitted in the trumpet housing (6). It is centred by the three pins (20) (Loctite 638) and secured by the screws (16). Tightening torque 79 - 90 Nm (Loctite 242).
Clean the seal mating faces and the location of cups and cones inside the trumpet housing and on the shaft. The seal, cup and cone mating faces should be free of burrs and dents.
Smear the external surface of the seal (7) with Loctite 542 (metal cage).
Replacing the seal (7):

Without replacement of the shaft 2): So that the seal lip does not rest in the same place on the shaft, fit the seal 4 mm from the shoulder of the cup (8).

With replacement of the shaft (2): Position the seal 5 mm from the shoulder of the cup (8).

Lubricate the cups (8) (5) and Install them home against the shoulder.
Install the cage (4) home against the shoulder.
Install the three-lipped seal (3) home against the shoulder of the shaft.
Lubricate the shaft (2) and Install the cone (5A) against the shoulder.
Moderately grease the cone (5A) and the lips of seals (3) (7) (using BP Agricharge grease or equivalent).
Protect the splines of the shaft (2) and insert it into the trumpet housing. The lips of the seal (3) must be facing outwards.

Remove the shaft protection and lightly lubricate the cone (8A).
Reinstall the cone (8A), washer (9) and planet carrier (10).
Install shims to obtain the required preload.
Replace the plug (27) with a grease nipple. Partially fill the trumpet housing cavity between the cone (5A) and the seal (3) with BP Agricharge grease or equivalent. Take off the grease nipple and retighten the plug.

Preloading the axle shaft bearings

Place the trumpet housing assembly in vertical position.
Remove the screw (23) and the washer (24).
Seat the cones (5A) (8A) in their cups by turning the trumpet housing on its shaft.

Determine a thickness of shims (25) greater than dimension X in order to obtain a clearanceInstall the washer (24) and the screw (23) and tighten to a torque of 270 - 440 Nm.
Using a dial gauge, check the clearance by moving the planet carrier axially.
Remove the screw (23) and the washer (24). Depending on the dial gauge reading, remove the surplus shim thickness (25) in order to obtain a preload of: P1 = 0.025 to 0.125 mm Clean the tapping at the end of the shaft (2).
Reinstall the washer (24). Clean the screw (23) and smear it with Loctite 241. Tighten to a torque of 270 - 440 Nm.

Replacing the wheel stud

Drive out the defective stud using a bronze drift and a hammer.
Use a brush and some solvent to clean the serration marks left by the stud on the shaft flange. Dry off with compressed air.
Apply a few drops of Loctite 270 to the new stud serration.
Install the new stud over the serration marks left by the previous stud.
After checking that the splines are properly engaged, bring the stud head up against the inner flange of the axle shaft with a bronze drift.