dencordle

I changed my front and rear diffs. I put Castrol 80-90 in both (gl5) because I couldn't find any 75-90 where I was.
Is this going to hurt anything?
or do I need to hunt down some 75-90 and change it. I haven't driven anywhere yet.

underwoodtransp

no problems at all. If you tow alot eventually I would change it out to some 75-140 but it will be just fine. A few numbers wont hurt a thing. Now if you put atf or 5w30 in them I would be worried.... Just drive it and make the change next time. No big deal.

dencordle

Thanks, just needed some reasurrance, I forgot to get any additive for it so I am heading out to get some.

underwoodtransp

NO ADDITIVE!!! These new ones don't need it. You are wasting your money. look in the owners manual.

djbikeman

Limited Slip Additive is not required for the AAM 11.5 rear diff with TracRite (Limited Slip).

edit: Underwood must have been typing as I was, but hopefully you get the point.

dencordle

ok... the manual says 75-90 synthetic limited-slip AAM real axles do not require a limited slip additive. The 80-90 that I put in is not a synthetic limited slip oil.

Is it still ok?

underwoodtransp

yea I would just change it sooner like 15k or so.

dencordle

Sorry I must have been tryping the same time you were.

Ok I'm safe
Thanks guys.

underwoodtransp

now you've learned your lesson Next time you will shop around for a synthetic oil and modify the weight if needed.

dencordle

Yes I have learned. I was in a hurry yesterday and didn't have time to go somewhere else to find the right oil. but now I know

no_6_oh_no

Drive for a while first without the additive and see how it reacts. If it starts making noise and giving you problems then try the additive. Some diffs do not like the lack of the the modifier and start popping and banging on corners when warm.

Jeff in TD

I guess I will respectfully disagree with the group, in that if I were in your shoes I'd dump that stuff.

The difference in weight is slight, but I'd want synthetic GL-5 in there like the manual calls for.

There have been a couple of threads about people having rear ends redone under warranty, and if you didn't have receipts showing the the correct replacement oil every 15K you would give them something to argue about.

It wouldn't take long, or cost that much to swap it out for Synthetic.

CRXsi

I agree with Jeff in TD, I would also re-change it asap. The weight difference is minimal but non-synthetic would worry me. If you are unsure how a torsen diff works I would read the following or search more on google:

How a Torsen Diff Works

Even better How a Torsen works

A torsen diff relies on the gears being spread out against the case of the internal assy which provides friction and in theory reduces slipping....FRICTION! This is why I would be worried without a synthetic.

John Robinson

There is no way I would take a chance on this one, I would go down to my local friendley dodge dealer & get the good stuff. Thicker oil is not better oil. Even the large 18 speed trannys are running thinner oils these days, the thinner oil doesnt hold heat as much & it will flow better.

CRXsi

Just to confirm...transmissions and diffs are 2 completely different animals. Tranny's use light oil for a different reason...mostly having to do with syncro and gear design. I would however also recommend going with the Dodge approved fluid. I was talking with my Mobil 1 rep once and asking him if their gear oil would stand up well...his response, Yes it will however it won't have the special additives that are put into the factory Dodge oil for the exact tolerances of AAM. He recommended staying with the Dodge oil (even if it is bloody expensive). This doesn't mean that other synthetic oils aren't good but I do agree that sometimes there are additives and chemicals in the factory product that aren't announced yet are very benefitial.