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Old 01-27-2020, 06:31 PM   #1
truckin 79
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Changing rear end fluid posi or not

Did a 79 1/2 ever come with a posi rear end? I need to change gasket and fluid but did not know if I needed to add special posi fluid. I have a big oil sludge hanging under rear end and so I think it is leaking gear oil and needs changed.
thanks
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Old 01-27-2020, 07:45 PM   #2
Matt Man
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Re: Changing rear end fluid posi or not

Could have came with a g80 which required the additive. Once you have the cover off you will know if it has one or not.
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Old 01-27-2020, 10:30 PM   #3
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Re: Changing rear end fluid posi or not

Does it still have the spid in the glove box?...
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Old 01-28-2020, 07:59 AM   #4
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Re: Changing rear end fluid posi or not

I always used Carquest gear oil that works in either one.
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Old 01-29-2020, 11:02 AM   #5
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Re: Changing rear end fluid posi or not

We started using the Ford posi additive to anything with posi traction.
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Old 01-29-2020, 12:27 PM   #6
truckin 79
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Re: Changing rear end fluid posi or not

I do not have spid had to change glove box doors as hinge was gone. I just assumed most later trucks with be a one legger and no posi. I heard that if you go with Synthetic a person does not need to posi additive. Is this true?
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Old 01-29-2020, 01:30 PM   #7
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Re: Changing rear end fluid posi or not

Quote:
Originally Posted by truckin 79 View Post
I do not have spid had to change glove box doors as hinge was gone. I just assumed most later trucks with be a one legger and no posi. I heard that if you go with Synthetic a person does not need to posi additive. Is this true?
No synthetic fluid does not replace the posi additive.

This is a open rear end:


This is a g80 rear end:


The g80 in the half ton axles (12 bolt, 10 bolt) are not very good I would be surprised that it would still be in there. My 81 came with one but when I got the truck it was not there, just had a open diff.
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Last edited by Matt Man; 01-29-2020 at 07:49 PM.
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