Well, today was fairly productive. I got the rear Mag-Hytec from the Men In Brown today. So I took it, 12 quarts of Royal Purple and the Husky Liner mud guards that I got a few days ago over to the Auto Hobby Shop to do the deed.
Both covers came off easy but the rear had lots of dried mud and rust around the seal. It took awhile to clean the surface area with some emery cloth, but it came out pretty good. The new Mag-Hytec went on easy and took about 7.75 qts of Royal Purple 75W-140.
I decided not to change the front cover, but during this process I decided to change it the next time the service is due. Having a drain plug would be outstanding... Anyway, I filled the front with just under 3 qts of Royal Purple 75W-90.
The fluid I drained from both diffs ran out like water...
While I was at it I installed the rear molded Husky Liner Mud Guards. I like the look and they go on pretty easy so I recommend them.

 

got pics of the finished truck?

 

Good to know about the capacity, I think I am going to finally install the MH that is sitting in my garage this weekend......

I am going with 75W110 though

 

75w140 is not whats called for in the AAM axels.Chrysler built axels take that weight.Doubt it will hurt anything but fuel mileage maybe.Bet it gets THICK in Montana.Thicker is NOT always better.Less heat tansfer and I've read it holds heat more.

 

The reason for the 75w-140 is that we are going to be towing a 10K trailer 5,000 miles in the next month. Dealer reccomends the heavier weight for this trip. The heavier weight is better for the increased load and I feel better about it.

 

It does not call for 75w140 pulling 15k for 10,000 miles.The PERSON at THE dealer is WRONG.But what ever.

 

I checked my '06 chrysler service manual. It clearly states 75W90 Synthetic, no additive. Hounddog is correct.

 

Won't hurt anything but told the heavy fliud does not loose heat as well as the thinner.Wish someone had a temp gauge to the diff. and do a fliud swap and see.But the 140wt is not recomended by AAM or Dodge.The heavier wt.does have some effect on fuel mileage and I bet its REAL stiff cold.Dealer near me also pushes the 140wt.I KNOW why.Its easier on them! I think BG products also pushes a LOT of dealers to use the 140wt and ADDITIVE.It then goes into EVERY truck at YOUR exspense.Thats what I ran into at SEVERAL dealers when I asked what wt.they used in AAM axels.Oh BUT SO and SO says its OK.Well I use what is SPECIFIED and I did NOT want to PAY for ADDITIVE when it wasn't needed.I talked to AAM a couple years back and they said they DID NOT recomend the 140wt.I use Amsoil Severe Gear 80w90 in BOTH my trucks but my 06 Mercury Gran Marquis calls for the 75w140 and thats what is in it.

 

You keep mentioning that it must be thick when it is cold... Please explain this?
I am no expert but I thought, and still think, that the 75W stands for 75 which is the weight of the gear oil I bought and that they recommend and that the 'W' stands for winter, as in, how it will act in cold temps... 75W-90 and 75W-140 will react the same way and maintain a certain viscosity when cold.
Now the 140 IIRC will maintain a higher viscosity when warm, and provide an extra amount of cushion under load. The heat transfer you mention is likely to be affected though.
I am not an expert and only barely knowledgeable so I am not stating these things I am only trying to add to the conversation, if there is an expert please chime in. I do, however, think what I have said is true...

 

I hear you.All I know is try pouring 75w90 and 75w140 SYNTHETIC gear oil lets say at 32 degrees.There is a differance.I used some 75w140 full synthetic in a manual trans(in fact several manual transmissions) and in anything below 45 degrees it was next to impossible on first shift to second gear or any gear really.Trans was also just plain STIFF in ALL temps until vehicle really warmed up etc.until some miles and heat.Swap it back out for 75w90 synthetic and worked slick and as designed even in 20 degree weather.Had the oil company I dealt with pick up that 75w140 and had to drain it out of a number of customer vehicles as well as my own.Oil rep told me in cold there would be NO differance in 75w140 or 75w90.He was WRONG.I do NOT think the W stands for winter.It has to do with flow propertys at certain temps etc.Maybe someone with the real skinny on this will jump in.I say this also.I can remember hand pumping the 75w140 in the shop and pump was STIFF.Big differance same hand pump in the 75w90.My wife about beat me silly for putting that 75w140 in HER Maxima.I heard about it daily until I got the CORRECT weight gear oil back in it.Had some REAL unhappy customers also.It didn't give me a warm fuzzy feeling in differentials knowing what it felt like in manual transmissions and drained it out of them also.But hey my 06 Gran Marquis calls for 75w140 and I hear the newer Dodge corporate rear axles do also.

 

One tid bit of info, I am being stationed in Alabama in August so at least I won't have to deal with another Montana winter...
I hope that some of the characteristics that might be bennificial work in my favor over the next few months and next year when I change the fluid again I can change gears, so to speak.

 

 

I have those same splash guards front and back on mine.They fit good don't they?

 

I do like them, rather than the more 'industrial' types.

 

Will their molded splash guards work with the mopar fender flairs?