Inhibited Oil Solves Problem of Lubricating Pre-selective Gearboxes
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I N his paper entitled "The Lubrica tion of Pre-selective Gearboxes," which he read before a meeting of the Institute of Petroleum, on October 16, Mr. A. T. Wilford, B.Sc., A.R.C.S., A.R.I.C., reveals many interesting facts about the units installed in the vehicles operated by London Transport.
When this type of gearbox was first fitted in the Board's buses, trouble was experienced through severe oxidation of the oil, as was evidenced by the presence of a gummy deposit on the working parts of the box. At the best, this made it difficult to obtain a change of gear, and at the worst, many drivers found it impossible to effect a change.
The trouble, says the author, was eventually kept within bounds by modifications in the design of the gearbox, a reversion to a Pennsylvanian grade of oil conforming to 104-110 sec. Redwood at 140 degrees F., and an oil change after every 6,000 miles.
Amongst the lubricants investigated was an inhibited oil, which was allowed to run for periods in excess of the normal, its performance, however, being closely watched. Twenty-five gearboxes were involved in these tests, and at intervals of a few thousand mikes, samples of used oil were removed.
It was found that the viscosity of the oil remained practically unchanged. and that acidity did not exceed 0.2 mg. KOFfigrm. Despite the fact that the boRes were neither new nor .freshly overhauled, no fewer than 14 were still in service after 40,000 to 50,000 miles of running without an oil change.
Further tests proved so satisfactory that the lubricant—an inhibited turbine oil—was adopted in the pre-selective gearboxes of all vehicles operated by the Board. The oil remains in use for the life of the box—about 80,000 miles —and upon removal is clarified by Stream-Line filtration. This filtered lubricant is adjusted by the addition of a standard quantity of inhibitor, and is then passed out to garages for re-use.
Mr. Wilford refers to instances of gearboxes remaining in service for as long as 120,000 miles without an oil change. It should be mentioned that fresh oil is added about twice a year.
Towards the end of his paper, Mr. Wilford says, "There is an urgent need for a laboratory oxidation test which would produce results, acceptable to both sutiplier . and user, of sufficient reliability to enable the rejection of oils not likely to give a satisfactory performance in pre-selective gearboxes.
"Such a test woUld not dispense with the necessity for conducting service tests with an oil which reached the required standard, but might perthivits initial use in, say, 50 gearboxes instead of only six; and so reduce the time which must elapse before it could be finally approved."