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Tuesday, June 07, 2005
Ready Reference for Lubricant and Fuel Performance: "

Ready Reference for Lubricant and Fuel Performance

Driveline Lubricants - Automotive Gear Lubricants

API Gear Oil Designations (See API Publication 1560 for full description)

Service Designations in Current Use

Service Designations not in Current Use

BenzWorld : Viewing a thread: "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: dingbat@codesmth.demon.co.uk (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)

Pennzoil Frequently Asked Questions: "2. What happens if API GL-5 gear oil is used in an API GL-4 gear oil application?

API GL-4 and API GL-5 products typically use the same extreme pressure (EP) additive system, with the API GL-5 having about twice the concentration of a API GL-4. In service, these additives become active under extreme load and temperature when the protective oil film can be squeezed away. EP additives work by forming wear-resistant compounds with the metal of the gear tooth surface. As the gears mesh, these compounds shield the gear teeth from direct metal-to-metal contact that would cause wear and damage to the gears. If too little of the active additive is present, proper protection would be compromised. Too much of this additive could cause excessive chemical corrosion of the gear surface. If an API GL-5 gear oil is used in a application where API GL-4 gear oil is called for, chemical corrosion of 'yellow metal' components may occur, such as bronze synchronizers, brass bushings, etc. This may lead to shifting difficulties or shortened equipment life. "

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