LUBRICATION OF THE TRANSMISSION, ETC.
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A Previous Article Having Dealt with the Lubrication of the Engine, this, the Third Article of the Series, Deals with the Transmission and the Working Parts of a Chassis.
IT has been shown in the previous article that there are numerous features of design arid circumstances of running to be considered in an attempt to decide the grades of oils suitable for engines. The lubrication of the transmission and of moving parts of the chassis also requires due care in order that the wear and fear on heavily loaded parts shall be reduced to the minimum. The fact that some chassis parts are not so easily lubricated as the engine is no excuse for their neglect. The very fact that they are not so accessible means that repairs and renewals frequently involve considerable expense. Moreover, they usually work under less satisfactory conditions, making regular attention to lubrication of equal importance. It will be well to consider the essential properties required of the lubricant to be used for these parts.
Gearboxes and Back Axles.--For the gearbox and back axle the lubricant must possess the following properties:—
1. It must be of the proper character and consistency
to coat, follow and cushion the gears and to provide
adequate lubrication for the gear mesh. 2. It must be capable of thorough distribution to any ball, roller or plain bearing provided in the construction and be of such a character that it will not have a corrosive effect on the highly polished surfaces of the balls, rollers and races.
3. It should contain no insoluble matter, however finely divided or of whatever lubricating value, as, under running conditions, separation and precipitation of the heavier matter are bound to occur.
4. It should be of a body and character that (a) will minimize resistance and power loss from the churning action of the gears, that (b) will not channel, and (c) that will permit of gear-changing with the leAst effort.
• 5. It should be of a body and character that will prevent leakage from the gearbox or back axle under all operating conditions likely to be encountered.
O. It must be such that any metallic particles due to wear or careless gear-changing will fall to the bottom of the gearbox instead of remaining in suspension, whereby damage to the bearings or the gear teeth would be caused.
Thus, a consideration of the points at issue indicates the use of an oil of 'heavy body as being pre-eminently suitable for the majority of the present-day gearboxes and back axles manufactured.
The care exercised in the design, production and mounting of modern gears and in the choice of materials has contributed largely towards improved and quieter running. The wide adoption of ball and roller antifriction bearings has also accomplished much in this direction. Where a gear oil is used for the gearbox and back axle, it should be an oil high in lubricating value, which will allow the gears to engage smoothly and without noise and will not cause difficult operation in cold temperatures. This will prevent unnecessary wear, and will minimize frictional losses.
Where a grease is specified, great care should be exercised in its selection. Correct grease for general service is one that is smooth, light coloured and medium bodied, carefully manufactured and free from all particles of insoluble and non-lubricating matter ; furthermore, it must be absolutely free from acid and from filling or loading material of any kind.
Most gearboxes and back axles are designed for the use of a fluid lubricant; hence, if a grease should be used, indispensable oil leads may be choked quickly and will fail to function. This may probably involve a seized spigot bearing, rendering the gear change inoperative, and it may cause overheating and other serious troubles and damage to the gearbox.
With a new vehicle the gearbox and back-axle casing should be drained and supplied with fresh lubricant of the correct grade on the • completion of 500 miles. Thereafter they should be drained, flushed out with paraffin and filled to their correct respective levels every 5,000 miles in the case of bevel-gear drives and every 2,500 miles in the case of worm drives, but, owing to the large variations in oil capacities of the latter types, latitude must be allowed in the last-named figure. Care must be taken to ensure that the proper oil levels are maintained always. Most manufacturers provide a level-testing orifice, or plug, for this purpose, and where these are not observed the level of the lubricant may be gauged by removing the inspection plate in the case of the gearbox ; the oil should just reach the under side of the lower shaft. In the case of the back axle the oil should fully cover the teeth situated at the lowest part of the crown wheel, but should not reach the differential cage which carries the crown wheel.
Replenishment should be made every 1,000 miles or as may be found necessary, but regular attention is imperative.
The worm drive operates at a higher temperature than does the bevel gear, whilst the tooth pressures are very heavy and, again, there is a high rubbing speed, thus making the operating conditions severe. Most heavy commercial vehicles have top worm drives and the lubricant used for them must be sufficiently fluid thoroughly to lubricate the gear and its bearings. Too heavy an oil may " track " in cold weather and also fail to provide efficient lubrication of the worm thrust. The choice of a suitable lubricant is, therefore, a matter of considerable importance, as failure will mean costly replacements which require accurate fitting. At all times avoid the use of grease in worm-driven axles.
Clutches.—For the clutch the lubricant required, if any, will depend upon the type employed, as, primarily, • -two main classes are used, viz., " wet " and "dry "--but the clutch spigot and thrust bearings must not he neglected. To ensure easy gear-changing, regular attention should be given to the lubrication of these parts, a grease cup or oil feed being provided for this purpose. The grease cup should be given two or three complete turns daily and refilled as necessary, depending upon the amount of use. Town work calls for frequent clutch operation, whereas long runs in the country entail infrequent clutch usage.
With the " dry " clutch, this is generally either of the cone or flat disc type, the face or faces covered with leather or a fabric material such as is used for brake facings. Where leather facings are used, an occasional dressing of castor oil, sparingly applied, is all that is required to keep them in good condition, whereas fabric facings rarely require attention.
The " wet " clutch is usually of the multiple-disc type, and consists of a number of metal discs which are made either of steel or, alternately, of steel and bronze; it is housed in an oil-tight casing, the driving discs being mounted on splines machined in the clutch housing, whilst the driven discs are mounted upon suitable splines machined in the clutch centre. Where this type of clutch is not lubricated from the engine, special attention should be given to its lubrication. Too heavy an oil will cause considerable inconvenience when driving in traffic owing to fluid friction or drag which causes spinning of the discs when declutching, whilst too light an oil may cause abrasion of the working surfaces when accepting the engine load. Where these clutches are separately lubricated a light, free-flowing oil should be used.
At the end of every 1,000 miles the lubricating oil should be drained from the clutch housing, which should then be flushed with paraffin and replenished to the correct level with fresh oil. "Clutch slip" should not be permitted, or serious damage will result. The lever bearings of the clutch pedal should also be greased or oiled regularly, according to the type of lubricator fitted.
Universal Joints.—The universal joints in the transmission shaft of a commercial vehicle are called upon to perform a heavy duty, and, therefore, should be inspected and lubricated regularly and given careful attention. For an oil-retaining enclosed metal joint a heavy-bodied engine oil or fluid gear oil should be used. Where grease is employed, It should be one of medium consistency, a stiff grease being undesirable, as it may not reach all the rubbing surfaces, owing to the small degree of relative movement. It must be consistent in quality and must not separate or change in body (hiring use.
Leather muffs and protectors to exclude dust, mud and water are a distinct advantage when the joints are not self-sealing.
For grease-filled joints, attention should be given once every 1,000 miles; oil-filled housings should be examined and replenished every 500 miles or as may be found necessary.
Road-wheel Bearings .—Road-wheel bearings are arranged in some cases to use oil and in other cases grease, depending mainly upon the type of bearings employed ; these may be of the ball, the roller, or the plain floating type. The latter type calls for a fluid gear oil to ensure a perfect film over the whole surface of the bearing in spite of the heavy load pressures involved. Under normal conditions they must be lubricated twice weekly. The former types can use either oil or grease, depending upon the road-wheel housing and the sealing of the bearing against leakage. Gear oil is suitable, or a grease of medium consistency may be used. The grease cups or lubricating caps should have regular attention, according to the nature of the service. In some cases, rear-wheel bearings are lubricated from the axle casing, and under these conditions separate lubrication is unnecessary.
It is specially important to use a grease of sort consistency in wheel hubs employing roller bearings, otherwise there is a likelihood of " tracking " of the lubricant and rapid failure of the bearings.
Chains," Enclosed" type chains are lubricated usually from an oil bath, which forms part of the chaincase; this should .be replenished weekly with engine oil and the chain cases flushed out with paraffin, afterwards being periodically refilled to the desired level with fresh oil..
" Open " type chains should be kept well lubricated at all times, and a clean exterior should be maintained in order to prevent adhesion of mud and dust. In wer weather more frequent attention is necessary.
Chains will, be preserved in the best possible condition if they be taken off after every 2,000 miles, washed thoroughly in paraffin and, when dry, placed in a tray of adequate depth containing a suitable graphite grease, the tray being heated gradually until the grease is just fluid or melted. After the chain has soaked thoroughly, surplus grease should be wiped off and the chain replaced. When a fleet of vehicles is employed, It is a good plan to have some spare chains, so that, without disturbance of working, the chains from each vehicle may then in turn be cleaned, examined and treated as described.
Where this procedure cannot be conveniently followed the chains should be thoroughly cleaned and painted over with warm gear oil, which should be worked well into the joints.
Steering.—A vital and important part of the chassis which demands frequent examination and attention is c38
the steering. Heavy bearing pressures and shock loads are encountered in the steering worm boxes, necessitating the use of a heavy-bodied oil and, where oil cannot be retained, a suitable grease may be used to ensure perfect freedom of all working parts, enabling the steering to answer immediately to the slightest movement of the steering wheel:
Steering knuckles, pins and bushes also require ample grease or oil, according to the lubricator fitted. Weekly' attention is desirable, and it is preferable that the front axle be lifted by means of the lifting jack, as an easier path is thereby afforded for the lubricant to penetrate to all the working surfaces, particularly the steering swivel pins.
Water Pump.—The pump may be situated on either of the water pipes—the hot or the cold. A medium yellow grease is generally used in the cooler position, but where the pump is located on the front end of the cylinder block, as often occurs, a stiff grease is necespsaurryp.oseSpecial greases are frequently supplied for this Road Springs.---Neglect of lubrication of road springs results in excessive friction between the leaves and is a major cause of hard riding, breakage and annoyance. The spring leaves should be dismantled annually, the rust removed and all leaves examined for breakages, a thin coating of suitable graphite grease being applied between the leaves. A dressing of oil will assist in preserving the riding qualities of the chassis if applied to the springs when they become harsh.
Road Spring Shackle Bolts.—It is important that these bolts receive proper attention at frequent intervals. Where arranged for grease lubrication, a high; grade medium grease should be used. Where fitted for oil lubrication, the same oil as is used in the engine suffices, but gear oils may also be used Where the method of application is suitable.
Controls and Brake Connections, etc.—All control joints should receive attention every week, engine oil being.. used. Grease-lubricated bearings should receive attention daily, the grease cups being given a full turn daily and kept filled, a high-grade medium grease being
used. . 2
Engine Fan Bearings.—Cooling-fan bearings are generally lubricated with grease, but occasionally oil is used. A medium grease of high quality is desirable, and attention should be given daily. Oil-lubricated bearings should receive attention weekly, engine oil being used.
Propeller Shaft Plunging Joints—Where a plunging joint is fitted on a propeller shaft—splined type— a good quality graphite grease should be used, and this joint should be lubricated frequently, as it is constantly working when the vehicle is on the road. In some cases daily application of engine oil may be necessary.
Oil and Grease-gun Systems.—Simplified methods of chassis lubrication by means of suitable oil or grease guns are now generally employed. These appliances have made it possible to give attention more rapidly and with certainty. A medium high-grade grease or a heavy gear oil may be employed.
Front-wheel Brakes.—The regular lubrication of all joints in the operating gear should always be eftected in order to ensure equalization of braking effort, which is of the greatest importance. Much care in extensive adjustments may be entirely wasted if the joints are not free. Sometimes front-wheel brakes cause the front hubs to run at higher temperatures than normal, particularly.in town service, and it may prove necessary to use a slightly stiffer grease than would otherwise be the ease in order to prevent leakage into the brake drums.