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Just got done working on the Dana 60 in my '01 E250 van. I filled the differential case with gear oil until it started flowing out of the fill hole. Later, I came across the Motorcraft document below. It says not to use more oil than what is listed as the capacity. This capacity would not bring the level up to the fill hole - just slightly below.
So, I guess my differential is slightly overfilled. Question.. is there any harm? Should I drain 1/2 quart or so out of it?
I tend to believe people/techs fill the fluid till it runs out. If I am right, millions of cars are running over filled and they have no problems.
I agree. I'm guessing the whole assembly was designed to run on a certain amount of oil, and the fill hole is not necessarily designed to correspond to that level. But in some rear ends it's close and people just use it. Next time I change oil, I think I'll put in exactly 3 quarts and call it good. That would be just 1/10 quart over the spec.
Anyway, I'm still curious about Ford's warning not to overfill. What harm would having "extra" oil in the differential cause?
There are people/shops that lift the truck and fill the oil, there are other shops that have a drive on rack. Just the angle of the differential dropping is going to change the level.
It's wise to ask, but sometimes it just really does not matter.
If the axle housing has a functional vent, there should be no pressure build up.
If there is so much fluid that it interferes with the vent, it should just puke out the vent hose.
The axle housing is designed to hold proper fluid capacity for more than one gear set. If overfilled, it may cause more internal pressure than it was designed to hold. That is why FORD ENGINEERING gives a fill capacity amount for each application.
None the less, expelling fluid while going down the road is most likely going to cause future problem(s), one being a compromised/blocked vent. That vent is designed to do more than just expel an overfill situation.
If overfilled, it may cause more internal pressure than it was designed to hold.
How much pressure differential at any one time is there in a differential. Yes, if the vent is plugged, the pressure will change and therefore fluid will push out. But a properly working vent on the top of the differential is not flowing a lot of air in either direction. Slightly over/under filling is not going to change that flow.
When we are talking about over filling, I am not talking about filling it up at the vent until it does not take any more. I believe the slight difference in filling with the differential hanging or loaded on the ground is not going to ruin anything. If it did, there would be a huge problem that EVERY shop would know about.
As for capacity how does one know if the differential is completely empty? I certainly would not use that as a fill amount. I would use that value as a guesstimate on how much oil I have to order for the job. Certainly a way to bill for the right amount used.
Again, I am talking about an once, not quarts or gallons. I think everyone can agree, if you over fill it that much, something is going to happen.
I always fill to the fill plug hole, then I take it somewhere where I can tilt the rear axle each way fairly well to get gear oil out to the bearings, then I check/fill again to the fill plug hole.
If it were up to me to guess, I'd guess that the factory-described fill level passed all of their rigorous testing so they decided that this is the correct fill level. "Over"filling by filling to the fill plug hole will make no measurable difference in anything.
One might assume (including me) that Ford specifically placed the fill hole location so that the bottom of the hole corresponds to the correct, as-designed fill amount. But that's really just an assumption. The fill hole might be there, or anywhere above that location.
One might assume (including me) that Ford specifically placed the fill hole location so that the bottom of the hole corresponds to the correct, as-designed fill amount. But that's really just an assumption. The fill hole might be there, or anywhere above that location.
- a$$-u-me -
If that were true, FORD would have had to drill & tap a different fill port for each separate rear housing according to each gear set installed and recommended lubricant level(s) for each gear set.
If that were true, FORD would have had to drill & tap a different fill port for each separate rear housing according to each gear set installed and recommended lubricant level(s) for each gear set.
Now that would have been a nightmare.
Wouldn't it be more like for a specific rear end set, like 9", 8.8", 8", 7.5",... each having its own carrier size, would have its own position for the fill hole? Even if you somehow installed an 8" gear set into a 9" pumpkin, one of the major differences is how much clearance the ring gear has from the bottom of the housing. The axes of the gears are going to be at the same place as those of the 9" set, so you need to have the same level of gear lube in the housing to have the gears properly immersed.
