Thread: 9 inch ford rear end

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I'll probably regret this but since these threads come up for review by people using search engines it helps to clarify some things for posterity.

First, if you look at the chart I linked, you'll see the '76 rear is 2" wider than the '73.

Second, if you're relying on a warantee to be backed by a supplier (perhaps such as the Currie example) you'd be wiser to follow their recommendation rather than trying to beat them in an argument, especially using potentially self serving info from say a lubricant suppliers site. Mike's comment about needing to have or add a friction modifier for the clutches is technically accurate, but you might still lose the argument and not have a manufacturer caused failure paid for. Being right and getting reimbursed are two different things.

Third, that being said some manufacturers may be way off base. RJ, if what you relayed is 100% accurate rather than your best recollection or interpretation, then BDS doesn't understand lubrication very well, or doesn't believe their customers have a clue and are trying to take an easy out. They're pretty bright folks there, so it's hard to believe they are clueless about lubrication. A link to the comment would have been useful in clarifying. Viscosity is measured by an ASTM standard. The test doesn't care whether its a mineral oil or a synthetic. Viscosity is a measure of rate of flow at a specified temperature. As an example, a motor oil with a set of two numbers, e.g. SAE 5w20, means that the oils viscosity is expressed at two temps, 0*F (the W designates winter so flow at low temp is important), and at 210*F. A single grade such as SAE 30 is an expression of the rate of flow at 210*F only. Perhaps BDS is trying to say that a synthetic (multigrade by design) MOTOR OIL, shouldn't be used because of it's light viscosity at low temps which might be insufficient to protect the gears at start up.

Fourth, codi might not have gotten an answer originally because his question wasn't directly related to the original intent of the thread. Sometimes it's better to start a new thread if your questions aren't exactly related to the original topic.

Lastly, making cross comparisons doesn't always work. For the sake of brevity there are essentially three types of gears; spur, helical, and hypoid. The spur gears have straight teeth and are a rolling motion between the opposing gear teeth, a pretty easy to lube environ, viscosity can handle it entirely (assuming load to gear size design is correct). Helical gears have angled teeth and the tooth interface has a slight amount of sliding action that usually requires an anti-wear additive (dependant on tooth angle, load, etc.) to help protect the teeth. The hypoid gears (typical to rear ends) have a relatively severe twist to the gear teeth which results in the tooth interface experienceing entirely sliding action. This requires an extreme pressure additive to prevent accelerated wear. What works for a spur gear won't work at all for a hypoid.

Blowers typically have spur or helical gears to syncronize/drive the impellers/screws and are nowhere as demanding as a rear end. Very different working conditions without a comparison of wear action. Similarly, the high temperature of a jet engine has no correlation to the operating conditions experienced by a motor oil. It is accurate that synthetics first came into use because of the unique application perameters of the turbine engine, but their impressive performance there doesn't automatically mean they're good in everything.

That being said, I am not arguing that synthetics can't work in an automobile engine. They have some very good performance characteristics that can be useful, especially at very low temperatures. And I don't intend to get into a debate over whether or not someone is crazy to be for or against the use of synthetics versus minerals, it's like religion, make the choice you feel best with. I won't try to convert you, don't try to convert me, whichever way you perceive my bent.