Fluid Change Questions

Chuck FB · June 8

3 hours ago, Core-Lokt said:

I think the Banks cover is higher capacity, given I don’t see oil in the sight glass. They say to observe factory capacity over sight glass. I used approximately 6 1/4 pints bc I assume not being able to fully drain bags, and a tiny bit of spillage when I squeezed. Got Amsoil ATF as-indicated on their website.

I have gas engine and six speed. Transmission service will happen after the transfer case and front differential (I’ll likely get another cover with drain, also). Besides the dipstick mod, idk what’s all underneath the pan.

That is an odd comment Banks would have about the volume given that the sight glass is there for the specific reason to allow for not only bringing the level to that range but to visually be able to check at any time that the diff has a sufficient level. I know its been commented that what GM claims is the volume required for the rear diff ends up falling short of what it actually takes if filling it to the bottom of the factory level plug, and the fact that GM ( actually the axle manufacturer ) is underfilling the diff at their factory below their own specs as mine was as well which has been a whole other issue and is leaving the oil down almost a quart low from full. As I read about the Banks cover instructions right on their webpage, they do say to go by the sight glass ( half way up the sight glass on level ground ) unless the vehicle has had the pinion angle changed due to a lift etc that throws off the factory pinion angle. I'll put it this way, if I installed a Banks cover on my own stock truck I would fill it half way up the window and then recheck after the truck has been driven and sat for hours while sitting on level ground to confirm the level.

Core-Lokt · June 8

I’m going off the instructions.

Chuck FB · June 8

1 hour ago, Core-Lokt said:

I’m going off the instructions.

Yes I read that as well on their website and its all in how its interpreted for one thing and I believe the GM spec itself does not call for enough volume to bring the oil level up to the bottom of the factory covers fill/level port which also is puzzling. Banks are also bouncing between two different truck makes in the instructions since both the Ram and the GM use AAM axles with those instructions.

The problem with not seeing the oil in the window is that one has no idea where the actual level is. Certainly anyone else on here reading this and having worked with the banks covers should chime in as they may have more information to provide. I am just simply concerned because I don't want to see someone underfill the diff as its not just the diff that is critical to lubrication, its the wheel end bearings. The dealership I bought my truck from had two HD pickups a while back have their rear wheel bearings fail because of being too severely underfilled at the factory and no one had checked and topped them off at the dealer but luckily warranty paid for a whole new complete axle housing as it mangled the axle housing spindles when the bearings failed and sent metal throughout the whole diff.

Core-Lokt · June 9

I agree it's ambiguous, and somewhat complicated with a shared application. For S&Gs, I just looked on Amsoil's website for a 2023 Ram 2500 with 6.4 gas. https://www.amsoil.com/lookup/auto-and-light-truck/2023/ram/2500-pickup/6-4l-8-cyl-engine-code-j-esb-j/

There's a lot of listings for Ram rear differentials, and too early in the morning to dig into the variants. But there's a big difference in fluid volume called for between them and GM applications, assuming it's the same axle assembly.

So, if GM differentials tend to be underfilled, what does everyone think about a 7 pint fill, as opposed to the 6.3 pints listed on Amsoil's website? It would somewhat conservatively split the difference between Ram and GM specs.

Chuck FB · June 9

I did a search outside of this forum and came across a thread from this forum from two years ago which was amusing but one I recall now from a trusted member who had himself had to add a quart on his brand new truck to bring it up to near the level plug level. Then after accumulating 5000 or so miles on the truck he pulled the cover to drain it out and wiped out the bottom of the diff housing and put the factory cover back on and in his case it took exactly 4 quarts to bring it up to within that 4/10 of an inch below the fill/level check plug, far more than the GM spec. That is a big difference between that GM spec ( which is why the GM diffs are below the level they themselves say they should be when coming out of the factory ) vs what amounts to around 8 pints of oil.

My own truck when I first got it home from new, I had not measured how much volume mine took since I used a hand pump on a 6 gallon pail of gear oil to top it off but I had measured it by using a bent wire on the flat shop floor after the truck sat overnight and a ruler and it was exactly 1" below the bottom of the fill hole on the rear diff. That fell right into line with what others have measured from a factory filled rear diff on these HD trucks, however the GM instructions are to fill from within between 4/10" of an inch or up to the bottom of the fill/level check hole as the full range. So that is why it alarmed me when you mentioned not seeing any oil in that window although I wasn't sure if that diff cover held the exact same amount as the factory cover so can only speculate its probably very close to retain the same oil flow characteristics over the top that the ring gear provides with the factory curved cover vs some of these odd flat back diff covers ( the whole video Gale does on that about some of the goofy after market covers out there ).

Core-Lokt · June 9

Good find and points, sir.

Core-Lokt · June 13

Thinking on things over the week, I decided to use the remaining oil in the pouch. Basically, there's a gallon in the differential, minus a tiny bit of spillage and whatever remained in the bags.

I think Banks designed this cover biased towards the standard Ram fill (some of those applications are greater than others, but by Amsoil's website, capacity is minimum about a pint greater than GM applications. In the picture, the differential appears fairly tilted, but it is really slightly tilted; the camera angle is skewed.

With ~8 pints, the level is midway on the sight glass; you can see the center hole of the baffle to more closely judge the level. Regardless the 6.3 pint fill spec, I'm going to leave it as-is. I don't blame Banks for erring on the conservative side, and I don't know why there's such a difference in specs between GM and Ram. And I'd also speculate the cover volume is pretty much the same as the stamped steel, as @Chuck FB noted relative volume with his recollection of another member's fill experience.

Chuck FB · Thursday at 07:34 PM

I changed the factory fill oil in the rear diff of my truck for the first time today and the miles is close to 9000 on the truck. There was a lot of fines on the magnet, a very thick layer but working it through my fingers it all felt like mush and as most know it appears like graphite, so no surprise chunks anyway. Certainly was time to do it from my thinking and could have been done sooner but the oil didn't look awful but sure wasn't new looking and never expected it to either. I did use some solvent to help me clean out the bottom area of the axle housing, just get any other stuff settled at the bottom washed and wiped out of the housing for the bit of effort it takes. I used Amsoil Severe Gear 75W90 in the easy packs to try out what they are like and I used up 4 packs and didn't spill much at all in the process but did take all four of the packs and go to the work bench and emptied them into a measuring container and there certainly was some in them that added up to something, then poured that into one of the easy packs and squirted in what I could get out of it. I would say the level is within 1/8th of an inch of being level with the threads at the fill plug so just the perfect amount. Once again, more than what GM says the fill volume is but computes with what others are adding to their rear diffs as well.

Z45 · 2026-07-03T13:50:31Z

I would be surprised if the diff's were not filled (with the cheapest gear lube) at the axle factory before being shipped to GM. If you ever watched them building trucks they install the axles and all suspension parts with the frame upside down and then turn it over before its time to install the engine.

Too much gear lube in a axle can be worse than not enough especially with a lower quality GL where is get whipped up with entrained air (foam) weakening its ability to lubricate.

Chuck FB · 2026-07-03T14:07:08Z

3 minutes ago, Z45 said:

I would be surprised if the diff's were not filled (with the cheapest gear lube) at the axle factory before being shipped to GM. If you ever watched them building trucks they install the axles and all suspension parts with the frame upside down and then turn it over before its time to install the engine.

Too much gear lube in a axle can be worse than not enough especially with a lower quality GL where is get whipped up with entrained air (foam) weakening its ability to lubricate.

There would be one way of determining the quality of the factory oil although probably more than a typical oil lab test, and that would be to draw out some oil from a new truck and send a sample to a lab that could do a more elaborate test of the oil. The issue with too little oil in the diff may not be the lack of lubrication of the diff bearings and gears themselves ( although a lack of oil volume for cooling ) but the wheel bearings because at some point the oil would be too low to properly get onto the spinning axle or fed along the axle tube. That was the claim by the local dealer from a couple of trucks in recent years that had the wheel bearings fail and they figured from lack of sufficient oil due to a severe underfilled diff and some of the bearing material made its way to the diff and it got damaged as well so the axle housings were just replaced on warranty. But your right that if the diff is over filled by whatever margin that it causes more churning of the oil than is desirable and that is no good either and can cause a pinion seal to leak. Also old oil I believe can tend to loose some of its properties like antifoaming and another good reason to change the diff oil every so often.

Core-Lokt · 2026-07-03T17:34:21Z

I got the time to change the fluids in the transfer case and front differential, and I intended to replace the front cover. This is a PML cover, and the noteworthy things about it are all hardware is there, the fill plug level is the same height (but on the side), and it holds a pint more per the instructions. There's no good place to take a pic, so that's the best I could do.

Chuck FB · 2026-07-04T13:45:43Z

19 hours ago, Core-Lokt said:

I got the time to change the fluids in the transfer case and front differential, and I intended to replace the front cover. This is a PML cover, and the noteworthy things about it are all hardware is there, the fill plug level is the same height (but on the side), and it holds a pint more per the instructions. There's no good place to take a pic, so that's the best I could do.

Would this be the first time both the diffs and transfer case oils were changed ( that is if you know the history of the truck since new ) and if so how many miles are on the truck now. Also and of course that would make all the difference if this was the factory oil or had been changed prior, what volume of wear metal fine paste like substance were on the rear vs the front diff cover magnets.

So far I have drained the rear diff oil and the transfer case as I said above at 9000 miles but don't have a clue what would be on the front diff magnet and would be speculating to guess it surely couldn't be near as much as what the rear diff magnet had on it due to it going along for the ride a large part of the time. The transfer case I have has the 4 auto feature which I have tried to avoid using as much as possible due to warnings about the clutch pack slippage wear that takes place, certainly I saw some discoloration of the oil but it still easily identified as red fluid but the fact it has no magnet isn't impressive but I think most transfer cases over the years never had a magnetic plug.

Core-Lokt · 2026-07-04T14:34:49Z

I bought the truck new in December 2022, and it's got 60,000 miles. The front cover magnet had slightly more glitter, but overall very clean, no off odor, and good-colored; really nothing to report. My truck has Hi-Lo transfer case, and the fluid looked great, as well. I have towed..maybe 1,000 miles. Yes, this was the first change for all three driveline items. I'll probably do the transmission at next oil change.