Changing rear end fluid posi or not

[truckin 79]

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?

[Matt Man]

Originally Posted by truckin 79

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.