Continuously Variable Transmission (C.V.T.)

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Continuously Variable Transmission (C.V.T.)

Post by Duvel78 » 20 Oct 2006 02:36 am

[a special thanks to Mac for this article!]

Important note: please don't copy this article without the permission of the authors / V3M; thanks!

Brief History

The Volvo 343 was the end of a line of small cars designed and developed by DAF (van Doorne's Automobiel Fabrieken) in the Netherlands.
Beginning at the 1958 motor show with the launch of the 600, the Daffodil (31,32, & 33), 44, 55, 66 &46 followed. In 1975 Volvo took over DAF and the 'on the drawing board' 77 model (codenamed P900) became the Volvo 343.

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As with previous Daf models, the 77 was designed for the Variomatic transmission which had been designed by Dr. Hub van Doorne.
Consisting basically of pairs of expandable pulleys linked by rubber-composite drive belts the Variomatic gave infinitely variable gear ratios between '1st.' gear and 'Overdrive' The ratio being determined by various factors such as road speed, throttle position, brake pressure and engine speed. Volvo called the Variomatic the C.V.T. (continuously variable transmission AKA constantly variable tranmission).

Definition of terms

Throughout this guide various terms will be used and it may be helpful to the 'technically challenged' if they are briefly explained in the context of their use here.

Vacuum - Air pressure less than that of ambient (ambient barometric pressure - the pressure of the air in which we live - varies from day to day but is generally around 1 bar or about 14.7 psi.). A vacuum is generally created in an enclosed space (a chamber) by lowering the internal air pressure (simply described as 'sucking the air ouf) Ambient air pressure then acts on the outer surface of the space in which the vacuum has been created. On a car a good source of vacuum (the suck) is the inlet manifold.

Gear ratio - Simply put the difference in size between gear wheels or pulleys. A small gear or pulley linked by a belt to, or geared to, a larger gear or pulley must rotate more than once to turn the larger, one turn. A large gear or pully turned once will however turn a smaller one more than once.

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Overdrive - If a driving gear and a driven gear are of equal sizes they have a gear ratio of 1:1. ie the driven wheel turns once for every turn of the driving wheel. If the driven wheel is smaller (and therefore turns more than once for each turn of the driving wheel) an 'overdrive' ratio is present, (see illustration above). In most modern cars with a 5 speed manual gearbox 4th.gear will have a ratio of 1:1 whilst 5th.gear will give an overdrive condition.

Centrifugal Force - The imperative for a mass rotating about a point to move directly away from the centre of that rotation. This force increases in proportion to the speed of rotation. Simply put - if you spin something, anything on it tends to get flung off.
Variable Diameter Pulley - A pulley comprised of two halves, the effective diameter of which may be varied by moving the halves apart or together, allowing or forcing the drive belt to move up or down the cone shaped inner surfaces.

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A brief overview of the system

A centrifugally operated clutch unit is fitted to a conventional flywheel bolted to the rear end of the engine crankshaft. Drive is transmitted from the clutch centre plate by a short quill shaft, to a lightweight aluminium propshaft, and thence to a primary transmission unit. The primary unit accepts drive from the propshaft, turns it through 90 ° via a bevel gear, to a cross shaft carrying a pair of variable diameter pulleys. The primary unit also contains the forward and reverse gearset and the 'park' mechanism (both of which operate on the drive to the cross shaft). The gear lever is connected by a rod to a lever on the top of the primary unit casing, between the pulleys.

Drive is then carried by a pair of rubber-composite drive belts to the secondary unit. The belts transmit the drive forces by friction from and to the sides of the belts and the coned faces of the pulleys.

The secondary unit consists of another cross shaft carrying a second pair of variable diameter pulleys. The casing also contains a reduction gear train and a conventional differential. Drive is taken to the wheels by driveshafts with CV joints (constant velocity joints).

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The propshaft is constructed of lightweight aluminium to minimise out of balance forces as it will always be turning at engine speed whenever the clutch is engaged, even when the transmission is in neutral, (gear selection takes place in the primary unit).

A description of the components of the C.V.T.

The Clutch

The clutch, whilst being fitted to a conventional flywheel, and having a friction centre plate very similar to a manual transmission, operates in an entirely different manner. In a 'manual' transmission clutch the centre plate is clamped tightly between the surface of the flywheel and the friction surface of the cover plate by either a diaphram spring, or on earlier cars (say before 1965) a number of coil springs. The centre plate is only able to revolve freely when the clutch pedal is depressed. In the C.V.T. system however the friction surface of the cover plate is actually held away from the centre plate by 3 light coil springs.

Between the cover plate body and its' friction surface are loosely sandwiched 3 steel rollers resting in tapered grooves (or tracks) radiating away from the centre. Due to centrifugal force, when the engine is running, the tendancy is for these weighted rollers to move outwards along the tapered tracks. This forces the cover plate friction surface away from the cover plate body (which is bolted to the flywheel) which forces the linings of the centre plate against the flywheel and the clutch becomes engaged.

At idle speed the coil springs hold the cover plate surface away from the centre plate to allow gears to be engaged and to prevent 'creep in gear'. As the throttle is depressed and engine speed increases the clutch progressively takes up drive. Again due to centrifugal force, the higher the engine speed becomes, the higher is the clamping force on the centre plate.

If the clutch is correctly fitted and adjusted it will begin to engage at an engine speed of between 1000 and 1150 rpm. By 2500 rpm. the clamping force will exceed 103Nm and will continue to climb as engine speed rises.
One problem arises during cold start/drive off - the engine speed with the choke engaged is higher than 1150 rpm. To allow forward or reverse to be engaged under these conditions the clutch housing is fitted with a vacuum operated servo which acts on a release arm carrying a bearing. This partially counteracts the centrifugal weights by depressing release fingers on the cover plate. This, when correctly adjusted can delay full clutch engagement until 2000 rpm. The servo is operated by engine vacuum via an electrically engaged valve triggered by a microswitch operated by the button in the head of the gear lever.

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The differing adjustment will be covered in the section on servicing.

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The Propshaft

The propshaft is comprised of a hollow aluminium tube with bonded-in rubber bushes at each end.

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Passing through, and bonded to, the bushes, are internally splined steel tubes into which the clutch drive quill and primary unit input shaft fit. The propshaft couplings are not clamped to the clutch and primary unit shafts, but a spring at the rear (between the rear bush and the primary unit) serves to tension the shaft. In addition when the propshaft is refitted after removal the splines of the couplings and those of the clutch and primary unit shafts should be coated with an adhesive compound 'High Tack', Volvo part no. 1161077 (if it is still available).

The Primary Unit

The Primary Unit is located at the rear of the car and consists of a gear case with a splined input shaft connected to a cross shaft by a bevel gear set. This gear set also includes a sliding mechanical 'dog' clutch to facilitate forward, neutral and reverse. A 'park' position is incorporated. Forward gear is selected by engaging a sliding collar into mesh with one of a pair of bevel gears on the cross shaft. The sliding collar is splined to the shaft and hence transmits the drive. Reverse is selected by engaging the other bevel gear. Neutral position is a mid-way point where neither bevel is engaged. When 'park' is selected the cross shaft is mecanically locked. At each end of the cross shaft are variable diameter pulleys consisting of inner pulley halves fixed to the shaft and outer pulley halves splined to the shaft that can slide in and out to vary the diameter of the pulley.

The outer pulley halves are comprised of a drum shaped housing with a coned inner face. The housing is divided by a diaphram into two chambers (inner and outer). The inner chamber contains a pair of centrifual weights pivoted on a carrier on the cross shaft. The weights are shaped so as to act on the inner face of the housing when under centrifugal force, causing the housing (outer pulley half) to move inwards along the cross shaft (increasing the effective diameter of the pulley). The inner chamber also includes a light diaphram spring to ensure the outer pulley half remains in contact with the drive belt when centrifugal force decreases.

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In addition to centrifugal force causing the pulleys to change diameter, engine vacuum is used to influence their operation. The diaphram dividing the outer pulley half housing is fixed to the cross shaft. A pipe connection is provided to both inner and outer chambers such that engine vacuum may be applied to either.

Evacuating the outer chamber (applying vacuum to it) will resuit in the pulley half moving inwards, whiist evacuating the inner chamber will cause the pulley half to move outwards. The principal is that reducing air pressure in the outer chamber (reducing its' volume) allows ambient air pressure to act on the outside of the housing and as the diaphram is fixed, the pulley half moves inwards. Reducing air pressure in the inner chamber causes the opposite. It can be seen therefore that engine vacuum can be used to assist or oppose the opération of the centrifugal weights.

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The Drive Belts

The belts are constructed of a rubber compound with reinforcing synthetic cords running along them. They are of toothed design but the drive is taken by the sides of the belts not the teeth. The teeth give stability to the belt during operation. Originally the belts were produced only by Goodyear and supplied only by Volvo but as the 300 series has aged other suppliers have appeared. The belts fit over the Primary Unit variable diameter pulleys and link them to the expandable pulleys of the Secondary Unit.

The Secondary Unit

The Secondary Unit consists of a gear case with drive input via a cross shaft. The shaft drives a reduction gear train and conventional differential unit. From the diff. The drive is taken by driveshafts, fitted with constant velocity joints at each end, to the rear wheels.

The cross shaft carries an expandable pulley at each end. Unlike the primary unit, the outer pulley half is fixed and the inner half can move in or out. The moving halves have no actuation or control mechanism but 'follow' the operation of the primary pulleys. At rest the pulley halves are held together by a strong diaphram and coil spring. During operation as the diameter of the primary pulleys increase the belts are'pulled' into the 'V of the coned faces - thus reducing the diameter of the secondary pulleys and raising the gearing. As the diameter of the primary pulleys reduce, the secondary pulley springs close the halves together - increasing their diameter and lowering the gearing.

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To facilitate adjstment of the drive belt tension, provision is made for the secondary unit to be moved forward or backward in its mounting frame controlled by a threaded adjusted between the casing and primary unit. The adjustment is determined by the measurement between the secondary pulley halves.

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Differences in gear levers

All C.V.T. equipped cars have a conventional looking gear lever, allbeit with only 4 gear selection positions P R N D. The selection system has an inhibitor switch (as in all modern automatics). The only real difference is the placement of the microswitch that operates the clutch disengagement servo. On very early (1977, 1978) cars the microwitch is in the head of the gear lever whereas in all later cars the switch is at the base of the lever and is operated by a rod from the selecto button.

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The Vacuum System

As previously described, rotating weights, under the influence of centrifugal force, serve to effect a change of gear ratio both up and down by causing the outer halves of the primary unit pulleys to move in or out. In addition to this purely mechanical system engine vacuum is employed to assist or oppose the effect of the weights. This is done by evacuating either the inner or outer chambers of the primary unit outer pulleys, connecting them to a vacuum source via a control valve known as the 'four way vacuum valve'.

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The valve is mounted in the off side of engine compartment just in front of the fuse box. It is flexibly fitted to a metal plate by three rubber bushes.

The unit is comprised of two separate valves, each with is own control solenoid operated by 12v. The unit has a single pipe connected to the engine inlet manifold, (in fact to a spacer plate fitted below the carburettor), to provide a source of vacuum. A pipe is connected to a source of filtered air at ambient pressure (the air cleaner) and two pipes run to the rear of the car where they are connected to the inner and outer chambers of the primary unit moving pulleys. One control solenoid connects the outer chambers to the vacuum source and the other solenoid the inner chambers. It can be seen that applying vacuum to the outer chambers will cause the outer pulley halves to move inwards, thus assisting the centrifugal weights to 'change up' the gearing. Applying vacuum to the inner chambers will cause the outer pulley halves to move outwards thus opposing the action of the weights.

As described, the 4 way vacuum valve is divided into two 'sides' - they are termed the 'Brake' side and the 'Overdrive' side. The brake side applies vacuum to the inner chambers of the primary pulleys and the overdrive side to the outer.

Refer to the section covering the Primary Unit for details of the vacuum pipe connection to the outer pulleys.

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The electrical operation of the 4 way valve will be covered in the next section.

Engine vacuum is also used to operate the clutch disengagement servo (see section covering the clutch for details). In this case an electrically operated valve is used to connect the clutch servo to the source of engine vacuum. A pipe runs from the valve to a T piece in the vacuum source pipe that goes to the 4 way valve and a second pipe connects the valve to the servo. The servo is mounted in the engine bay low down on the N/S.
The following line drawing shows the location.

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The Electrical control System

As stated the 4 way vacuum valve is operated by electrically controlled solenoids which are themselves controlled by various switches and, on vehicles from 1978, a speed sensing relay - the Tachometric Relay, (contains two relays, one speed sensing and one changeover (switches from one contact to another)). A almost every CVT car will have the later system I shall describe that first and note any differences later.
An overall wiring diagram should help.

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This shows the location of the various electrical components on the car.

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Each of the possible operating senarios will now be explained.

1. Engine is started and is at idle speed.

The Tachometric Relay receives a speed signal from the Renix unit (or coil on pre 84 cars), but as the engine speed is below 1750-1850 rpm. The tacho relay remains open (current cannot pass). The changeover relay is activated, its' trigger coil being supplied with 12v from fuse no. 8 and being earthed through the high pressure brake, throttle cable and low ratio hold switches, all being closed. Neither solenoid of the 4 way valve is activated so no vacuum is directed to the primary pulley chambers.

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2. Normal acceleration and cruise.

As the engine speed exceeds 1850 rpm. and the centrifugal weights begin to raise the gearing (as the vehicle drives off), the tacho relay closes, allowing 12v, supplied via the still activated changeover relay, to flow through the overdrive solenoid of the 4way valve and to earth through the tacho relay. The solenoid operates, opening the primary unit pulley outer chambers to vacuum thus assisting the gear ratio 'change up'.

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3. Kick down.

If full acceleration is required a means of lowering the gear ratio is required. This is achieved by depressing the throttle fully to operate a switch built into the throttle cable. This opens removing the earth of the changeover relay coil allowing the relay to switch contacts. 12v (from fuse no.8) is now removed from the overdrive solenoid of the 4way valve and applied to the brake solenoid. This opens the primary unit pulley inner chambers to vacuum and opposes the action of the centrifugal weights. The gear ratio reduces (changes down). Relaxing the throttle restores the changeover relay earth - the relay chages back - and once more vacuum is directed to the pulley outer chambers.

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4. Normal braking.

Under normal braking (brake pressure in the master cylinder less than 20kg/cm 2) the electrical control condition is identical to the overdrive condition ie:- the overdrive solenoid is in operation, (the transmission relies on decaying road speed to 'downshift' by a reduction in centrifugal force.

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5. Heavy braking.

Under heavy braking it is desirable not only to provide extra engine braking (by lowering the gear ratio) but also ensure that the transmission is in a lower ratio for when acceleration is resumed. This is achieved by a pressure sensitive switch fitted to the brake master cylinder. This is normally closed but opens when brake pressure exceeds 20kg/cm 2. This switch is in the changeover relay earth line and works exactly as in the kick down situation.

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6. Low Ratio Hold.

A further switch is fitted to the changeover relay earth line, the low ratio hold switch. It is fitted to the gear lever console and may be used to prevent 'change up' and give engine braking when (for example) descending a steep hill. It also works by redirecting vacuum to the primary unit pulley inner chambers to oppose the centrifugal weights. Operating the low ratio hold switch also directs 12v from fuse no.20, through a bulb and to earth through the throttle cable switch. This illuminates the L.R.H.switch, (and also creates an anomaly in that full throttle with the L.R.H. switch engaged will put the warning light out).

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The clutch disengage servo vacuum valve works in a slightly unexpected way in that it is activated as soon as the engine is started, if the gear lever is in 'P' or 'N'.

The valve is supplied with 12v from fuse no.8 and is earthed through the start inhibitor switch (in pos. 'P' and 'N'). When the interlock button in the head of the gear lever is depressed a switch operated by it takes over the earth as the gear lever is moved into 'D' or 'R'. When the lever has been moved and the button is released the earth is broken and the vacuum valve closes (removing the vacuum supply and opening the clutch sevo to ambient air).

Ignition on - Gear lever In position 'P' or 'N'.

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Gear lever being moved to position 'D' or 'R'.

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As previously stated the vast majority of CVT 300s effect control of the 4 way vacuum valve by means of the speed sensing capability and changeover relay of the Tachometric relay Unit. 1977 model year cars however employed a simpler system.
With the engine at idle, the overdrive solenoid of the 4 way valve is supplied with 12v from fuse no.3, through a microswitch on the throttle linkage of the carburettor (which is open at idle). The solenoid is earthed by a normally closed switch on the throttle cable (where it passes through the bulkhead).

On opening the throttle, the carburettor microswitch closes when engine speed reaches 2650 rpm, activating the overdrive solenoid. For full throttle kick down, the throttle cable switch is opened (by fully depressing the throttle pedal), which removes the solenoid earth, deactivating it, and removing vacuum assistance to 'change up'.

Under braking the throttle closes, opening the carburettor microswitch, and deactivating the overdrive solenoid. At the same time the brake light switch supplies 12v, from fuse no. 13, not only to the brake lights but also to the brake solenoid of the 4 way valve.
Power to the brake solenoid (but not the brake lights) is looped through the Low Rario Hold switch. The solenoid is directly earthed.

Operating the low ratio hold switch supplies 12v from fuse no.2 to the, now closed switch, to the brake solenoid, and to a warning lamp in the instrument cluster.

The clutch disengage vacuum servo valve on these early cars operates in the same way electrically as later vehicles (although the microswitch is located differently.

Service and adjustment of the C.V.T.

There are a number of service requirements specific to the C.V.T. Transmission.

Every 6000mls(10000km):

Check secondary unit pully gap (belt tension)
Adjust if necessary.
Visual inspection of drive belts.
Ensure cooling vents in front bumper are clear.

Every 12000mls(20000km):

The above plus
Check adjustment of centrifugal clutch. Adjust if necessary.
Visual inspection of primary and secondary units for oil leakage.
Check speed sensing function of Tachometric Relay.

Every 24000mls(40000km):

The above plus
Change oil in primary and secondary unit gear cases.

As condition dictates:

Replace drive belts.

Checking and adjusting the Secondary Unit pulley gap

I have suggested that this operation is to tension the drive belts but this is only partially correct. It is true that if there is no secondary unit pully gap at all the belts will be too slack and may well slip (and overheat and degrade) but by setting the pulley gap too wide you will reduce the highest gear ratio available It also may overtension the belt and therefore destroy them! The gap is adjusted by moving the secondary unit backwards or forwards on its support frame which has the effect of 'pulling' the belts into the spring loaded pulleys (or the opposite).
Raise the car on ramps or stands securely. The rear wheels must be free to turn. Remove the inner transmission guard plate from under the primary and secondary units (held on by 6 bolts).

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Drive Belt check

Whilst the vehicle is raised and the transmission guard is removed a visual inspection of the drive belts should be carried out, The whole length of both belts should be examined for condition.
The sides of the belts should be free from cracking or flaking but evidence of light wear and 'polishing' is normal. There should be no evidence of pieces breaking away and no lumps or distortion.

The top surface of the belts (opposite to the teeth) should be smooth.
Light cracking between the teeth is quite normal but deep cracks extending to the outer edge is not. If the cracks have reached the reinforcing cords a corresponding depression will be felt on the top surface, and in such cases the belts must be replaced.

In my experience the life of a set of belts is very variable - depending on car use and location - anywhere between 15000 mis.and 70000 mis. If the CVT pulley coned surfaces are damaged or corroded (perhaps by little use over a long period) belt life could be very short indeed !!.

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Some belt noise is to be expected and is not to be considered a defect. In fact noise level varies from supplier to supplier. Genuine Volvo (Goodyear) belts are probably the quietist (but again from experience may not last quite as long as belts from some other suppliers). In general the longest lasting belts are the noisiest, (harder rubber). Refit the transmission guard.

Cooling Vents.

In use the belts and pulleys can get quite hot, and are cooled by air flowing through grilled vents in the front bumper and along the chassis box sections (the air emerges just in front of the primary unit pulleys. Ensure that the vents are free from any debris that might restrict air flow.

Checking and adjusting the centrifugal clutch.

The centrifugal clutch cover is bolted to the flywheel with adjusting shims between them. The pressure surface is held away from the flywheel by light coil springs. At rest the centre plate (aka friction plate) revolves freely between them. It is this clearance between the friction plate and the pressure surface that is checked and adjusted. As the clutch wears this gap increases as does clutch engagement speed.

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Raise the car on ramps or stands securely. Ensure that the clutch disengage servo adjusting nut is slackened off. The clutch bellhousing is furnished with cut away areas to give access to the 3 pairs of clutch cover plate securing bolts and adjusting shims - and to allow measurement of the center plate to pressure surface clearance. Measure the clearance using feeler gauges . The correct gap is 0.1 - 0.5mm. If adjustment is required this achieved by changing the shims which are available in a number of sizes, a combination of which will cover any adjustment need. Note:- If after adjustment the shim thickness used is 0.7mm. with a correct gap, it indicates that the centre plate is worn and need replacement.

The following shims are available from Volvo:

0.5mm part no.3268618
1.2mm part no.3264403
1.5mm part no.3264404
1.8mm part no.3264405
2.1mm part no.3264406
2.4mm part no.3292198

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When you are satisfied that the clutch adjustment is correct you must then adjust the disengage servo such that a gap of 1 - 1.5mm. exists between the clutch release arm and the clutch bellhousing aperture through which the arm passes.

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For very early cars up to chassis no.314541 (with internal servo spring) the adjustment proceedure is different.

Turn the adjusting nut anti-clockwise until the the diaphram in the servo touches the servo wall. Remove the vacuum hose and insert a depth gauge into the servo pipe. Turn the adjusting nut clockwise to draw the diaphram away from the servo wall by a distance of 7.0mm. (referral to the diagram of the clutch in the components description section should make this clear).

Check Primary and Secondary units for oil leakage

This is self explanatory and should be carried out when checking the drive belts.

Check speed sensing of Tachometric Relay

Place your hand on the overdrive solenoid of the 4 way vacuum valve and with the engine running at idle, increase the engine speed to 2000rpm. At about 1800rpm. you should feel the solenoid activate.

Primary and Secondary unit oil change.

Raise and support the car on ramps or stands but keep the vehicle level (an angle will affect oil level when refilling the units). Remove the transmission guard. This operation should be carried out after a drive to warm the oil (much easier to drain).

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Remove the drain plugs 2 & 4. Allow the oil to drain. Replace the drain plugs using new sealing washers. The same washer part no.947624 is used for both drain and filler plugs. x4 required. Remove the filler plugs 1 & 3 and fill the units until the oil just runs out of the filler plug holes.
Refit the plugs, again with new washers.

The capacity of the primary unit is 0.55lt and that of the Secondary unit 1.Olt. Use a quality transmission oil grade SAE80W-90. (under very cold conditions ATF type F or Dexron may be used). You can purchase suitable oil in plastic bottles complete with flexible spouts which make filling or topping up easy.

Replacing the Drive Belts

Replacing the drive belts is well within the capabilities of a competent D.I.Y. mechanic. As for previous servicing, raise the car on stands or ramps, but is necessary to be able to turn the rear wheels.

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For this task both the inner and outer guard plates should be removed.
The inner plate is held on by 6 screws (2) and the outer by 12(1).

As for belt adjustment, slacken the secondary mounting nuts and the adjuster lock nut, and move the secondary unit as far forward as possible, (the belts as slack as possible). Remove the 2 vacuum pipes from the connections on each outer cover of the primary unit outer pulley halves (2 pipes each side). As they are of different sizes it is not necessary to mark them for reassembly. The belts must now be brought to the bottom of the secondary pulley cones (so that the pully halves are fully apart). Ideally you should use Volvo special tool 9995837 (which looks like a large 'G cramp) to force the belts between the pulleys. A spacer should now be inserted between the pulley halves to keep them apart when the belt is removed. Again if possible use Volvo special tool 9995936.

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Both of the above illustrations show the early version of the tool, the currently available spreader looks like this.

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If, as is most likely, you do not have access to the Volvo special tools, all is not lost. The secondary unit pulley halves can be separated by pulling down hard on each belt in turn as shown. A 'home made' spacer can be fabricated from wood and used instead of the factory version.

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With the belt pulled into the secondary pulleys, and the spacer inserted, pull the belt into the primary pulley (probably already fully in). Slip the belt over the rim of the secondary unit outer pully half first, and then remove the belt from the primary unit. Repeat with the other belt.
Fitting the new belts is a reversal of removal. Hang the belts over the primary unit pulleys and pull down to fully separate the halves. Slip the belts over the outer rims of the secondary unit pulleys, pull hard down to separate them and remove the spacers. Rotate the rear wheels to move the belts 'up' the secondary pulleys and adjust the belts as has been previously described. New belts should be re-adjusted 3000mls (5000km) after fitting, and thereafter as per the service schedule.

Appendix 1

CVT Specifications.

Total transmission reduction (with secondary pulley gap of 1.5mm)
From a minimum of 4.00:1
To a maximum of 14.15:1

Primary unit reduction ratio = 1.53:1
Secondary unit reduction ratio = 4.51:1

Secondary unit pulley gap.
Checking = 1.5 -2.0mm
Setting = 1.5mm
Minimum = 1.5mm

Lubrication Primary and Secondary units.
SAE 80W - 90 gear oil to API GL-4 or GL-5. (Nordic markets ATF A/A, F, or Dexron)
Primary unit capacity 0.625lt. (oil change 0.5I1).
Secondary unit capacity 1.12lt. (oil change 1.0lt.).

Within sliding pulleys.
ATF type A/A, F, or Dexron.
Primary unit capacity 100cc per side.
Secondary unit capacity 75cc per side.

Tachometric relay switching speed 1750 - 1850rpm.
Carburettor microswitch (1977) switches at 2400 - 2600rpm.

Appendix 2

The internal arrangement of the Tachometric Relay showing the speed sensing relay and the changeover relay in a common case.

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NB: Slight amendments courtesy of Antiekeradio. Many thanks to him :)

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