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Oil Changes, All-steel Differentials

15th January 1965
Page 35
Page 35, 15th January 1965 — Oil Changes, All-steel Differentials
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APART from some oil-seal failure calling for additional topping-up amounts, the oil in a vast number of goods vehicle diffs can be left undisturbed for quite long periods. Mileages of 100,000 between complete drain and change are not unknown with units using bronze worm wheel and steel worm shaft. It can be said with some certainty that this particular style of rear-axle unit has served the industry very well indeed. In cases where careful tyre matching ensures normal running temperature, the high mileage obtained probably does little more than colour the oil with a harmless bronze silt, noted in the light of a lamp held behind the draining oil.

However, for those who believe oil to be the cheapest commodity, cliff oil would not be worked beyond 40,000 miles, and there are some dedicated engineers who stick rigidly to the maker's drill book and use a much lower mile

age. With the heavier vehicles, particularly the tractive unit on single drive. the all-steel diff is the answer to increased power, higher speeds and two extra tyres on the road. But now, instead of a harmless mixture of bronze and oil, there is another brew being created when high mileages are run between oil changes. This is steel debris, and the attack made upon the duff mechanism is centred around the bearings, when clearances can be rapidly widened—together with pitted tracks—if the oil is left undrained for long periods.

As an example, after a series of failures to heavy diff bearings, which pointed to abrasive lubrication, three magnetic drain plugs were fitted to obtain the measure of the debris, and the next draining of each diff programmed for 30,000 miles. The result of this test was staggering, as each magnetic plug had such an accumulation of steel whiskers that it almost

resisted withdrawal on leaving the threads. The test, however, provided an answer in two parts: for all-steel diffs. programme oil changes for 20-25,000 miles—or equip each casing with a magnetic drain plug.

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