I tried doing a search of this, but did not have an luck. I have a 2000 Cherokee with an 8.25 in the rear. I do not used my car for any type of towing, or off roading, or anything other than normal, everyday driving. My owners manual recommend 75w90 for the fluid, which is what I've used in the past. Well, I was looking in the factory service manual, and that says use 80w90. It is a service manual for my year and make (and it's a service manual, not an after market haynes or anything like that). I'm confused by that. I am very much a "by the book" person. I know some people say with high mileage to use different viscosities, but I like to go by the book, but now I'm confused, since the owners manual, and the service manual contradict each other.

I'm doing the fluid in both the rear and front differentials. I rebuilt the rear diff in July of 2010, and think I might be hearing some bearing noise from back there, which I really hope I don't, I really don't want to rebuild it again. I decided it is time to change the fluid, to look for metal in it. If I don't see metal in it, the noise I am hearing is more than likely just tire noise. I am all but sure my front diff is going bad, but if that one goes bad...my car will just become 2 wheel drive with sandbags in the back during the winter, I'm not about to rebuild an "optional" differential haha.

Thanks in advance to any input anyone has about my fluid issue!

 

80 90w lucas fluid.
ive never had issues in any of my 6 jeeps..
bit more costly.. but worth it imo.

http://www.lucasoil.com/products/dis...id=12&loc=show

 

I just put Royal Purple in the front and back last weekend. its heavier weight than what you're looking for (but the correct weight for tow package and potentially towing a load).

If you have an LSD dont forget to avoid using brake cleaner in the pumpkin, and to add the LSD formula... Royal purple has it in there already, as do some other synthetic oils

From what I have heard, make sure to use synthetic oil. There really isnt a good reason not to

 

75-90 or 80-90 will work fine. The difference is mechanically insignificant. I personally use synthetic as the cost difference is minimal for something that I change every 30k, but plenty of people use conventional lubricants with no issue. As long as it isn't left in there for 100k!

 

I have never used synthetic oils before. Is there a problem going from a regular conventional oil to a synthetic? I have heard you can't ever go the other way, from synthetic to conventional, without flushing it out. I just want to make sure conventional to synthetic won't be a problem. Also, does anyone know why there is a contradiction between the owners manual and the factory service manual? I know the difference between 75W90 and 80W90 is minimal, but I am a "by the book" person, so it bothers me why there's a difference. Maybe I should call a service department and ask.

 

There is no issue with going from conventional to synthetic. Period. Nor is there an issue with using 80-90.

But by all means, call the service dept. if you don't believe this. They will confirm.

 

If you have the proper tools why not rebuild both the front and rear if necessary? You must really drive the crap out of this thing to burn up a set of bearings in a year!

 

I don't have alll the proper tools. My sisters ex-husband helped me do it, and he had tools like to measure the backlash and things like that, that I could only guess on. Obviously, unless it is needed, I don't want to ask him to help with the front one too. I have figured out where my front diff problem is coming from (I think), so I don't think it is bad anymore. When I replace something Thursday, I will know for sure. I no longer think my rear diff is making noise, I think I'm just overly paranoid, since that was a fairly major job to do. It must be tire noise