Workshop -Transmission

Details for this section are for the Lambretta 175 Li Series 1 and 2 however there are many similarities between these models and other models of Lambretta threewheelers/Lambros. This information and the pictures included are provided from the 'Instructions for Repair Shops' for these models published in 1963. It is intended for informational purposes and we would recommend seeking professional advice before undertaking anything described in the Workshop section.

Rear Axle

The rear axle (Fig. 29) consists of a central differential casing in light alloy, containing the differential unit, and two flanged tubular arms attached to it.

The oil filler and level plug are placed at the rear of the differential box, while the drain plug is placed underneath same.


The differential unit (Fig. 30) consists of a bevel pinion supported by two ball bearings situated with their oil seals in the flanged bush on the front of the box, and the differential casing containing two satellite gears, two gears and the crown wheel. The box itself is supported by two ball bearings force fitted into their seats in the arms.

The arms, which are of different lengths (the right hand being longer than the left hand arm), support the rear wheel hubs while the driving action to the rear wheels is through two half shafts, one on each side, which are splined to the planetary gears at one end and to hubs at the other. The half shafts can be pulled out from the differential box without dismantling the wheel hubs, but only removing the drive flange in the wheel centres.

The lubricant to be used is SAE 90 EP Gear box and differential oil, and the quantity required from empty to the oil level is 6.35 ozs.
When flushing the rear axle, i.e. after long periods of usage or at the oil change, it is advisable to use one of the oil companies recommended detergent oils and NOT paraffin.


Adjustment of the crown wheel and pinion
If the adjustment of the bevel pair group has not been carried out correctly, abnormal noise will occur during running. This must be eliminated as soon as possible, as bevel gears running out of correct mesh deteriorate very rapidly and a delay would render the attempt of adjustment useless. Bear in mind that wear and deterioration of the pinion and differential ball bearings can bring about this trouble.

A bevel pair is correctly adjusted when the play between the teeth is between 0.07 and 0.12 mm, and the contact zone of the teeth in mesh is about in the middle of the tooth width.

The play between the teeth can be measured according to the play on the rear yoke arm splined sleeve which can be felt by hand when rotating before the movement actually affects the crown wheel. Said play, measured in correspondence to the centres of the yoke arm holes, should be only up to 0.2 mm.

The contact zone of the teeth can be easily ascertained, by blueing the pinion teeth, refitting back and turning the pinion by hand a few turns, and then extracting the pinion for the check.

To adjust the bevel pair, proceed in the following manner :

Change: the gasket 18330208 ( available 0.5 - 1 - 1.5 mm thickness) placed between the flange bush support the pinion group and the differential casing, thus varying pinion position,

The shim 41042014 placed between the differential box and bearing on the crown wheel side, that is the left hand axle arm. The substitution of this shim, available in 1.8 and 2.2 mm varies the position of the crown wheel. Bear in mind that the variation of the shim thickness 41042014 must also be carried out on gasket 41042029 or between left hand axle arm and differential casing, so that the play between the differential box and its supporting bearings is not altered.

They play should not normally be more than 0.1 mm, but in the meantime not be zero to avoid overloading the ball bearings, which otherwise will deteriorate very quickly.

The gasket 41042029 is (was) available in the following thicknesses : 0.2 mm (paper) - 0.3 - 0.5 - 0.7 mm.



Lift the rear of the vehicle by placing the jack in correspondence of the first transversal frame beam, behind the gear box, and add two stands one at each rear frame extremity.


To detach the rear wheel hydraulic brake tube; unscrew the two hexagonal unions connecting the tubes with the shoes brake cylinder (10 mm spanner), release the clips fixing tubes to the rear axle, loosen the nut fixing the three way union to its support (14 mm spanner) remove the three way union, de­tach the tubes from the axle.


To detach the hand brake controls: unscrew the screws fixing the cable trunnion screws (8 mm spanner) and detach the cables.


To detach the rear axle from the frame: open the front transmission coupling hose rear clip, drain oil from differential, pull out the split pins of the spring pins and with 17 mm spanner unscrew the nuts fixing the pins. With the proper punch ease first the front and then the rear spring link pins (Fig. 31). Note : Between the rear links and the springs two bronze washers are inserted. Remove the rear axle complete with wheels and springs, sliding the transmission shaft from the splined sleeve at the gear box end (Fig 31 bis)


To remove the rear wheels: unscrew the four dome nuts on each wheel (14 mm spanner) fixing rims to the hubs and remove the wheels from the hubs, (Do not unscrew the other four nuts).


To dismantle the rear hubs: unscrew the six screws ( 11 mm spanner) locking the hub driving flange, and using two of the screws as extractors, screwing them into the two threaded holes, remove the hub flange, remove the gasket, straighten the tab washer locking the centering, withdraw the layshafts and then with the lock ring spanner unscrew the centering, remove the washers and with the same spanner remove the lock ring, fit tool 53289, fixing it with 3 screws to the hub and withdraw the hub with its bearings (Fig. 33).


To remove the brake shoes: open up shoes from the hand brake cam side, turn them 90degrees so as to bring them perpendicular to the back plate and remove them.


To remove the Back Plate : unscrew the four nuts (14 mm spanner) fixing the back plate to the flange on the axle arm, remove the washers and then the back plate (Fig. 34).


To remove the rear springs: unscrew the four nuts (14 mm spanner) of the two U clamps fixing the springs to the axle, remove the washers, the U clamps and then each spring,


To remove the transmission shaft: unscrew the three nuts ( 14 mm spanner) on the rear yoke arm, re­move the washers and the bolts, detach the coupling with the transmission shaft.

Take care of the rubber dust ring of the centering guide.


To remove the differential : straighten the tab washers of the bolts fixing the arms to the differential box, unscrew 4 screws and 4 nuts (10 mm spanner) from the right hand side of the box, remove the right hand arm of the box by tapping with the mallet on the flange holding the back plate or the rear spring attachment, moving it axially. (Fig. 35 & 36).

Afterwards unscrew the four screws (10 mm spanner) on the left hand side, remove the screws and remove the rear axle box from the left hand arm (Fig. 37) then extract the differential complete with crown wheel and satellites.

Take care of the arms and axle box.


To remove the pinion : open up the tab washers, unscrew the 4 bolts (10 mm spanner) fixing the pinion bearing bush to the differential box and tapping the pinion through the box now without the crown wheel and satellites, extract it from its seats. Holding the coupling yoke arm, unscrew the nut locking the yoke arm (19 mm spanner) remove the washers, withdraw the yoke arm and by tapping, push out the pinion.



To remove the satellites and planetaries: remove the split pin of the satellite support pin, remove the washers, the satellite pin and by rotating the planetaries, remove the two satellites. By moving them towards the centre of the box, remove both the two planetaries. Take care of the shims. (Fig. 38).



To reassemble the rear axle, follow the operations in the reverse manner, bearing in mind the following.


To reassemble the planetary and satellite gears: refit with the interposing of the shims 40330228, the planetary gears into the satellite support box. Mesh in a diametrically opposite position the sa­tellites. Rotate the group so that the holes in the satellites come to coincide with the holes on the box, then introduce from the outside of the box, the satellite holding pin, fix it with washers and split pin.

Check the play between the teeth of the planetary and satellites (about 0.1 mm), otherwise substitute the shims 40330228 with others of appropriate thick­ness. (0.4 - 0.5 - 0.6 - 0.8).


To refit the pinion slide on to the pinion shaft the shims 41042009 and insert the pinion shaft into the bearings and distance piece fitted in the bush, then slide the yoke arm on to the splined end of the pinion; complete with dust protector ( 41044002 ) and interposing the washer, fix the shaft by tigh­tening the nut (19 mm spanner). When fitting the yoke arm be careful with the oil seal. Insert the pinion group and bush with gasket 18330208, into the differential box and tighten the four bolts.


To refit the differential; assemble the differential box with the crown wheel on to the left hand axle arm (short) taking care of the shims between box and bearing. Normally it is sufficient to fit one shim of 1.95 mm No. 410420141 control the parallelism between crown wheel and arm flange.

Fit on to the left hand arm the differenlial box, complete with pinion and carry out the adjustment of the bevel pair as laid down previously (see page 56).

When fitting the differential box to the arm, ensure its correct placing. The plate for anchoring the leaf spring to the arm should be in a position diametrically opposite to the drain plug on the box.

The bolts fixing the arm flange to the box must have tab washers fitted even if originally spring washers were fitted.

To reassemble the right and axle arm

Apply the arm to the box, taking care to fit the shim between box and bearing and to the gasket between the arm flange and axle box.

As said beforehand, it is necessary to adjust the thickness of the gasket between flange and differential box, so that the play in the box between the two support bearings be the least possible (it should not be higher than 0.1 mm) without however causing interference which could be dangerous to the bearings due to excessive axial load.