75W90 vs 75W140 - TCCoA Forums
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post #1 of 5 (permalink) Old 08-15-2008, 04:53 PM Thread Starter
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75W90 vs 75W140

Trying to decide which weight gear oil to use. I see both 75W90 and 75W140 recommended. Any suggestions on one over the other?


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post #2 of 5 (permalink) Old 09-16-2008, 10:56 PM
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75w90 is what you should use, 75w140 is to heavy of an oil. 1400hp pro stock cars run 75w90 i think you'll be ok. unless your driving a semi truck or dragracing an 8,000hp top fuel dragster they use 75w140 some 80w140. think of it this way: with 75w140 your trying to stuff pudding down a pin hole.....75w90 is way more thinner

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post #3 of 5 (permalink) Old 03-19-2009, 01:49 AM
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How many quarts of gear oil does the IRS take?
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post #4 of 5 (permalink) Old 03-19-2009, 06:43 AM
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Originally Posted by GilroyRacing View Post
How many quarts of gear oil does the IRS take?
If empty, it will take a little over 2 bottles. If you have a trac-loc rear, don't forget to add the trac-loc addivitive. Ford dealers carry little bottles of it and you only need one. IMO, don't use the bottles at the parts stores with the addivitve already in them.

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post #5 of 5 (permalink) Old 08-21-2009, 05:53 PM
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gear oil

All the truck diff manufacturers spec 75w90. Ford put 75w140 in mine. when I change mine I will go 75w90 synth with the friction modifier. If it can handle 2050 ft/lbs from an ISX cummins, I think it can handle my 4.6 torque.
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