GumpsVa

I have a 2004.5, 2500 4WD with 4:10 Rear, like to know the best gear oil for both diff and in the rear do I need to add additive for anti slip or do the new gear oils already include it?? Also plan to tow a 5th Wheel 12K GVW of trailer.



Thanks

KATOOM

Any of the few name brand quality synthetic gear fluids you can find at most parts stores will be just fine. Red Line, Royal Purple, Lucas, Amsoil, etc... (Amsoil only available by suppliers)

The fluid weight you want to run will be best based on such variables like the average climate you live/drive in, the weight you regularly pull, and the type of terrain (hills or flat).

torquefan

You won't need to add any friction modifier, as the limited slip units in the 3rd gen trucks don't have clutches.

Grit Dog

No additive needed.
I typically don't run spendy trendy oils except in things I don't want to have to maintian for a long time, like diffs.
Changed OE fluid for Amsoil at about 15kmi. Changed rear again around 100kmi, Amsoil. Just changed the front at 140k. Half Amsoil, half whatever the other bottle was in the shop! Fwiw after well over 100kmi the front oil still looked like new.

soulezoo

As said twice above, no friction additive needed as you have a worm gear type of anti-spin differential as opposed to the clutch pack type of limited-slip.

KATOOM also had good advise above.

Jeff in TD

After talking to folks at Redline about what to run in these AAM's, I went with 75-90 front and 75-140 in the rear, the regular stuff. They also make a version with no limited slip additive, but they said though AAM's limited slip doesn't require additive, most all oils have some limited slip additive, and the additive doesn't hurt anything and may actually reduce local temps. Also there had been some threads about binding when turning while running oil with no additive.

Anyway, if you tow heavy and live where it can be over 110f, a group 5 synthetic 75w120 or 75-140 in the rear IMHO would be fine.

GumpsVa

Thanks all for the answers that's helps me out a whole bunch. Will start changing soon

Jeff in TD

A couple things I'd mention: the factory torque spec (if I recall 24ft/lbs for the plug and 30ft/lbs cover bolts) I think is a bit high. Several folks have had bolts snap off before reaching 30 ft lbs, so you might consider not tightening them quite that much.

Also, shortly after the switch to AAM axles, a thing came out saying max oil level should be 3/4" below the hole on the 11.5, apparently to reduce risk of seal failure. Some
Of the later trucks have "fill level___" stamped on the rear cover, with the line below the level of the plug, but you have to be looking for the marking to see it.

KATOOM

30 pounds does sound high for those smaller bolts. I've always used RTV and just snug them up tight but not cranking on them.

As for the fill level..... Thats a well debated topic because you'll hear people try to argue that the seals will pop if its too full. But understanding the fact that a differential is vented, it would be impossibly to pop a seal unless the vent was blocked. And if that was the case then any amount of heat or pressure would pop a seal. Worst case scenario would be oil puking out the vent.

The argument of oil foaming isnt plausible either because the hypoid action of the R&P which is constantly churning the entire stock. Even if the R&P was fully submerged (impossible) what you'd get is more heat build up given the oil wouldn't be able to dissipate as well.

Rather making sure the oil level is high enough that its constantly bathing the outer bearings is most important. If the level is too low then the wheel bearings starve for lubrication and burn up. Considering off camber driving and turning should be considered too.

All that said, I've always filled my differential oil level until its spilling out the fill hole. On my Mag-Hytec I have the ability to run it even higher.....which I do.

Jeff in TD

These AAM's have nice reuseable rubber gaskets, which is nice.

On my previous truck I got through the first hangs fine, so I figured folks that reported broken bolts maybe got sketchy bolts but mine would be fine- but then one snapped on the 2nd oil change. Fortunately they seem to be easy to remove.

sojoe

you do not need synthetic oil in front diff according to my 04 owners manual. Just syn GL5 for rear dif.

ftltmp

Other than my truck being a 3500 dually, I have the same year and gears as you. I run Amsoil 75-140 in mine.