The following describes the rear hub, swing arm and suspension as fitted to a 04 S4R (Desmoquattro) the same system is also used on other S*R models.
Update. I had discovered an error in the previously stated 82mm, a couple of measurements were off. Now corrected and every thing cross checks. I have also included a drawing showing the suspension relationship. PM for a dwg. I apologise for the error.
Adjustments to the suspension, are outside the scope of this discussion.
S*R models use a single sided swing arm that pivots on the engine cases, chain adjustment is facilitated by means of an eccentric hub that carries the wheel axle, the suspension strut and a ride height adjusting rod are secured at their lower ends to the swing arm, the top ends are connecter to an unequal length rocker arm pivoting about a shaft fixed to the frame. The wheel has a specified travel of 148mm describing a radius of 530mm. The axis of the axle is offset by 15.5mm from the axis of the hub.
The suspension is rising rate, this means that the spring compression rate increases when the wheels move further into jounce. A rising-rate suspension maintains consistent ride and handling characteristics under a variety of situations: loaded or unloaded, straight roads or curves, and smooth roads or bumpy. The suspension has a 2:1 ratio.
The swing arm is a two part aluminium construction, the front part is cast and is welded to a tubular rear. The arm pivots on needle roller bearings two in each crankcase half .The pivot shaft is located in the arm by circlips at each end. The arm is clamped to the left hand end of the shaft with a cotter type arrangement, the right hand end is not clamped to the spindle.
Swing Arm and Shaft
A plastic chain guide is fixed to the front of the left hand arm to prevent contact with the chain both top and bottom.
The large bolts screwed into each end of the shaft, serve only to secure the inner component of the foot peg mounting elastomeric vibration isolation bush.
The location and axial play of the arm/shaft assembly is controlled by shims placed either side between the engine case and the arm, these shims also form the axial load thrust faces.This location of the swing arm to the engine, is critical to wheel alignment, according to the following table, the swing arm is referenced to the right hand mounting.
Measured Play Left Shims Right Shims
0.10mm --------- 1 x 0.10mm
0.20mm 1 x 0.10mm 1 x 0.10mm
0.30mm 1 x 0.20mm 1 x 0.10mm
The wheel axle hub is mounted in a bore at the rear of the swing arm, the bore is split and two 10mm bolts provide the clamping force to secure the hub. The hub is located axially by face to face contact with the swing arm. Rotating the hub within the arm causes the eccentric axle center line to describe a radius, this has the effect of varying the distance between the axle and the engine output shaft center lines. Rotating the hub also varies the ride height as well as the wheelbase.
The eccentric hub should be established with the axle below eccentric axis side of its adjustment. Operating it in the upper side has a significant affect on the ride height. The eccentric hub should nominally set the axle between the 4 and 5 o'clock position (viewed from the left side). The proper chain tension can also be obtained when the eccentric is in the wrong position - with the axle set between the 1 and 2 o'clock position.
The following table indicates the position of the axis relative to rotation of the hub. Note that the potential increase in ride height of 15.5.mm and the alteration of the wheel base of 31mm these are considered significant figures.
In practice however, it will be the chain/sprocket combination and their condition that will determine the position of the axle. The pic below, shows the position of the eccentric with a 15/44/104 sprocket chain combination, the axle is at the approximate 7 o’clock position, most probably the axle would be at the 6 o’clock position with the std 15/42/104 set up. and the factory ride height setting and wheelbase dimension reference against this axle position.
The table assumes a reference position of 6 o’clock. The ride height rod can be adjusted to compensates for any decrease in ride height as a result of the position of the eccentric.
Position Ride Height Chain Adjustment & Wheelbase
3 o’clock -15.5 +15.5
4 o’clock -13.4 +13.4
5 o’clock -7.8 +7.8
6 o’clock 0 0
7 o’clock -7.8 -7.8
8 o’clock -13.4 -13.4
9 o’clock -15.5 -15.5
The bearings within the hub consists of a needle roller on the wheel side and a double row angular contact ball bearing on the sprocket side.
The sprocket side double row angular contact bearing part number is SKF BAH 0062 and has dimensions of 35mm bore x 62mm OD. The design of the bearing provides for thrust load in either axial direction and serves to locate the axial position of the axle and the components mounted to it. The thrust preloads are set during manufacture. The bearing is a press fit into the hub bore and secured by a circlip. The bearing incorporates rubber seals on both sides and is ‘lifetime lubricated’.
Double Row Angular Contact Bearing
Sprocket Side Bearing.
The wheel side needle roller bearing is a Torrington NK42130A that runs directly on the axle, an oil seal is fitted into the wheel side of the hub bore
The hollow axle carries the rear wheel locating pins and the mounting lugs for the brake disc. It is drawn up tight to the sprocket side bearing by the left hand M33 nut. The rear wheel is mounted on the right hand end of the axle, located by four pins and centered by a conical spacer, it is drawn up tight to the axle flange by the right hand M38 nut. The wheel is driven by the frictional clamping force between the wheel and the axle flange. The drive pins serve to locate the wheel on the axle.
Rear Wheel Axle
The drive sprocket is fastened to the drive flange by means of five rubber isolated bolts, the drive flange is splined to the axle and is drawn up tight onto the angular contact bearing by the nut.
Sprocket Cush Drive Bolt
A limited amount of angular movement in both directions is afforded to the sprocket by the rubber bushed bolts, providing a cushioning affect to the transmitted load. The bore of the sprocket rotates on a spigot on the drive flange.
The rear 245mm dia brake disc is rigidly bolted to the axle with 4 M8 bolts, four ferrous buttons are riveted to the disc to provide pulses to the speedometer sensor.
A Brembo two piston caliper is fitted to the brake torque reaction plate the plate pivots on an extension of the eccentric hub, a slot on the plate engages with a pin fastened to the swing arm, the plate is rotates about its bore on the hub, and secured with a circlip, O rings either side prevent the ingress of water and dirt. The movement is required to compensate for movement of the eccentric when adjusting the drive chain tension.
The plate also carries the hall effect sensor for the speedometer input.
Brake Plate
The suspension strut (shock absorber) is a coil over de carbon type damper with a separated gas pressure reservoir. The Showa 44mm body and 14mm shaft shock has provision for preload, compression and rebound adjustments. The preload of the 56mm ID spring is adjustable by a threaded collar on the shock body, the spring has a free length of 200mm and the fitted length is variable from 175mm to 160mm depending on the preload setting, as delivered the preload is set to 172mm. There is no indication on the spring as to its rate.
The strut has an eye to eye extended dimension of 300mm and an effective stroke of 45mm (The shop manual states a stroke of 65mm but that is without the bump stop). A 20mm thick rubber bumper is provided at the compression extremity.
In operation, the strut is compressed from both ends by the action of the suspension movement.
Wheel travel is given at 148mm, this translates into the full 65mm metal to metal stroke of the strut. Using the effective stroke of 45mm plus 10mm of bump stop compression, the wheel travel is reduced to 128mm.
The graph below plots strut length against wheel travel.
Below is the relationship of the Swing Arm, Strut, Ride Height Adjuster and Rocker Arm.
The rebound damping adjustment is positioned at the rod end of the strut, clock wise rotation of the adjuster increases the damping and anti clockwise decreases the damping, the factory setting is 1 turn anti-clockwise from the fully seated position. The compression damping adjuster is located on the upper body of the strut, clock wise rotation of the adjuster increases the damping and anti clockwise decreases the damping, the factory setting is 2 turns anti-clockwise from the fully seated position.
Showa Shock Absorber
The suspension rocker arm pivots on needle bearings and has a liberal amount of end float, seals are provided to prevent the ingress of water and dirt. The rocker arm has a center to center dimension of 52.5mm for the ride height end to the pivot. The dimension for the similar strut to pivot side is 74.5mm, giving a ration of 1.4 : 1.
Suspension Rocker Pivot
The ride height rod is fitted with spherical bearings at each end, threaded left and right hand, turning the rod varies the eye to eye distance. The length of the rod is given in the shop manual as 261mm, this is incorrect, the measured ‘as delivered’ eye to eye measurement of the rod is 273mm the absolute minimum length is 270mm, and can be lengthened to 285mm
An increase of 3mm (1rotation of the adjuster rod), will cause a corresponding 6mm increase in ride height.
The lower ends of both the strut and ride height rod are free to pivot about an axis 100mm from the swing arm pivot axis, both are fitted with bushes, a bolt passes though a machined bore in the swing arm, tightening the bolt draws the bushes into contact with the swing arm and the component ends.
Operational Issues
The lateral location of the swing arm has an effect on both wheel and sprocket alignment. The procedure for measuring and shimming the swing arm mounting contained in the shop manual should be strictly followed.
The wheel is driven by the frictional clamping force between the wheel and the axle flange. The drive pins serve to locate the wheel on the axle. The securing nut should be torqued to the recommended figure of 176Nm.
Corrosion can occur between the bore of aluminium conical spacer and the axle. The fit between these components is critical to the concentric mounting of the wheel. Corrosion that has caused metal loss is grounds for replacement.
The elastomeric sprocket mounting studs have been known to shear, this allows the outer part of the bush to move out of the inside of the sprocket until it contacts the eccentric hub and proceeds to grind it away. After market sprocket carriers have a lip to prevent this. The OEM sprocket can be modified by center punching the inside edge of the mounting hole just sufficiently to cause a burr that will prevent the bush from passing though it.
Prior to removing the swinging arm, clean as well as possible the area around the arm/case interface.
When removing the swing arm pivot shaft cotter, first remove the nut then drive the bolt up from the bottom, do not try to turn the bolt out from the top. Pack the recess with grease.
When removing the pivot shaft remove only the right had circlip and drive the shaft out from that end, catch any shims that drop out as the shaft is withdrawn tag them right and left. Immediately stuff the pivot shaft bearings with a rags to prevent the ingress of dirt
The pivot shaft bearing surfaces are subject to localized wear due to the limited (14°) rotation and the relatively small contact surfaces resisting the directional load.
The pivot shaft is subject to corrosion between the shaft and arm, this can result in the shaft being difficult to remove, coat the shaft well including the bearing areas with a grease having good anti corrosion properties. The needle bearings in the cases should be liberally greased with the same product.
The ride height adjuster threaded ends are prone to seizing, these threads are not lubricated at the factory. It is recommended that the ride height rod be removed to make any adjustments, at this time the threads should be cleaned and packed well with anti seize. This may make it possible to perform future adjustments without having to remove the rod.
The rod ride height adjuster end bearings are maintenance free Teflon and require no further lubrication.
The foot peg elastomeric isolators on the ends of the pivot shafts, are mounted with the inner clamped to the swing arm by the large flanged bolt, check to ensure that a washer is fitted, otherwise the outer of the isolator will also be clamped and as this is fixed to the foot peg bracket, their will be resistance to the movement of the swing arm.
The rocker arm pivot bolt contributes to the frame stiffness, apply moly and torque to 75Nm.
When replacing the rear wheel, take care to ensure that the pins on the axle are correctly engaged into the holes in the wheel hub.
The torque applied to the two 12mm bolts that clamp the hub is critical, over tightening can cause the wheel bearings to bind. They should be progressively tightened in a 1 2 1 sequence until the recommend torque of 33Nm is achieved. Lubricate the bolts with moly prior to assembly.
Care should be taken when applying the not insignificant torque to the axle nuts, the nuts are somewhat slim and the socket can slip off . Speedymoto sells a tool that has a spigot that fits into the axle holding the socket in position.
Put a thin smear of moly on the thrust faces of the axle nuts, torque the 33mm sprocket nut to 156Nm and the 38mm wheel nut to 176Nm. When tightening the nuts, if the safety clip does not line up with the hole in the axle, tighten it to achieve the alignment.
Fix the ends of the locking clips together with a small cable tie, this will ensure the retention of the axle nuts.
Ducati “Forbids” the dismantling of the hub and it is only available as a complete unit
However, any competent shop could replace the bearings, proper drifts should be fabricated to press out the bearings, the sprocket side first followed by the wheel side needle bearing and seal. When fitting the bearings, ensure that the sprocket side is pushed fully home.
DO NOT drive on the inner race of the bearing.
Finding the SKF BAH 0062 double row angular contact ball bearing may be a problem, apparently it is not listed and the dealer has to contact SKF. Expect to pay $50 - $60.
The needle bearing can be lubricated but the ball bearing is sealed, when servicing the axle, check the rotation of the ball bearing by hand and examine the seals for signs of failure.
When assembling, grease all contact surfaces with a grease that has anti corrosion properties, Corrosion Block grease from Lear (the makers of ACF50) is an excellent product for this application, its lubrication properties meets or exceeds service classification NLG1. It can be used almost everywhere.
There are two castellated nuts on the strut body to adjust the spring preload, the thicker nut is the locknut (OD 70mm) and the thinner (OD 74mm) one is the adjusting nut. Due to the high torque required and the confined access, It is preferable to use the correct size hook spanners when making adjustments if the tool slips injuries to the hands can occur. The nuts are prone to seizure from corrosion, consideration should be given to the fitment of a hugger to offer some protection to the strut.
Spring Preload Adjuster Ring Nuts
From the information provided above, it is possible through a combination of sprockets and chain length to achieve a more favorable geometry setup. It is also possible to determine any ride height adjustments required as a result of a sprocket change or chain adjustment.
Where there is significant contact between the chain and the protector, the position of the eccentric should be considered when seeking a solution.
Correct adjustment for sag, is essential if the available stroke of the strut is to be utilised.
