BenzWorld Senior Member
Date registered: Aug 2002
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RE: Whats the importance of Non-Hypoid gear oil?
I had saved this information, this guy is so thorough that it needs no more explanations:
From: firstname.lastname@example.org (Andy Dingley) Newsgroups: rec.autos.tech Subject: Re: Hypoid vs. Non-Hypoid Date: Tue, 09 Jan 1996 17:45:49 GMT Mark <74551.2327@CompuServe.COM> wrote: >Can someone explain the difference between Hypoid and Non-Hypoid >oil? "Hypoid" is not really a question of oil, so much as a question of gearcutting. Old (1920's) rear axles used straight bevel gears to form the crownwheel and pinion. These had two disadvantage, the pinion shaft meets the crownwheel on its central axis, and the straight cut gears are noisy. By using a more complex "hypoid" gear tooth shape (if you look at a pinion, the teeth appear twisted) these problems can be addressed. The more gradual engagement of the teeth along their length reduces noise. By careful design of the geometry the pinion can be made to mesh _below_ the axis of the crownwheel. As the centre height of the crownwheel is fixed by the wheel height, this allows the propshaft to be lowered relative to the car body, giving a clearer floorpan and lower centre of gravity for better cornering. Hypoid bevels are now universal in this application. Because of the sliding contact that hypoid gears make, their hydrodynamic contact pressure is higher. To be suitable for use with hypoid gears, a lubricant must be capable of resisting high pressures. Oils with "EP" ratings (Extreme Pressure) such as EP90 are required. Some brands describe themselves as "hypoid" instead, a term which is synonymous with EP. GL-5 is a formal API standard for this type of oil (comparable to MIL-L-2105B/C/D) > The book is telling me to use Non-Hypoid gear oil 80W or >80W/90 on the manual transmission and GL-5 hypoid gear oil 90W on >the rear axle. A manual transmission won't usually contain hypoid gears, so it doesn't need an EP oil. Rare exceptions are those transaxles where the crownwheel and gearbox share the same lubricant. Although an EP oil is more complex to manufacture, it has no disadvantages when used in instances where the EP attribute isn't strictly required. Manual steering boxes and other slow-moving oil-containing components are often filled with 90 weight oil. It's usual to buy EP90 because that's what the axle requires, then use the same oil for all other components. There's little practical difference between 80 & 90 weights. I fill everything with EP80 and I've never had a problem. There's an increasing trend amongst manufacturers to reduce the number of different lubricant types required. My own gearbox (5 speed Range Rover) runs on ATF, but 20W/50 engine oil or EP90 axle oil are equally permissible. -- Andy Dingley email@example.com