Proper fill levelf for differentials?

[stchman]

Even since I was young, I had always been taught that a differential is full when the fluid comes running out the fill hole. The same was believed for manual transmissions and transfer cases.

Is this always the case?

My Silverado owners manual states this:

Quote:

For all 4.3 L, 4.8 L and 5.3 L
1500 Series applications, the
proper level is 1.0mm to
19.0mm (0.04 in to 0.7 in)
below the bottom of the fill hole,
located on the rear axle. Add
only enough fluid to reach the
proper level.


1mm to 19mm. Strance, it sounds like anywhere in-between that range is OK.

 

[Eddie]

Yes.

 

[4wheeldog]

Your understanding is true in most cases. Occasionally, manufacturers will give more convoluted instructions.

I had a '72 Ford Courier (Built by Mazda) that had maybe 75hp, and a rear end that looked like it would do duty in a 1 ton truck. The instructions for filling the differential started with lifting the rear wheels of the vehicle 12" higher the the front wheels. Pull plug, fill to bottom of threads. Why, I cannot imagine.

 

[DemoFly]

Mostly true, but not always the case.

A Mercedes ML350? I think it was had the fill hole above the axle tubes, to fill that diff to where it poured out would have been over 2 gallons considering I would have had to fill the axle tubes.

Some aftermarket diff covers have the fill holes higher than factory as well, so always double check.

 

[wirelessF]

My 02 has a instructional tag on the rear axle to fill it up until it's a certain height from the bottom of the fill hole. On Amsoil's lookup website that comes up to 4.9 pints which is shy of 2 1/2 quarts. When I first changed the gear oil when not reading the warning it took almost 3 quarts until the fluid started coming out of the fill port.

I'm guessing the gear oil was supposed to be at a low level so the oil does not go into the axle tubes.

 

[CT8]

It seems to be that level forever.

 

[Lapham3]

I think ther've been problems with some rear banjo designs where the lube can overload axle seals and goober up brakes, ect=think cranking hard through a freeway cloverleaf. Lowering the level helps that and the rear end still has plenty of lube to live.

 

[WyrTwister]

Originally Posted By: stchman
Even since I was young, I had always been taught that a differential is full when the fluid comes running out the fill hole. The same was believed for manual transmissions and transfer cases.

Is this always the case?

My Silverado owners manual states this:

Quote:

For all 4.3 L, 4.8 L and 5.3 L
1500 Series applications, the
proper level is 1.0mm to
19.0mm (0.04 in to 0.7 in)
below the bottom of the fill hole,
located on the rear axle. Add
only enough fluid to reach the
proper level.


1mm to 19mm. Strance, it sounds like anywhere in-between that range is OK.


That is the way I was instructed , also .

God bless
Wyr

 

[WyrTwister]

Originally Posted By: Lapham3
I think ther've been problems with some rear banjo designs where the lube can overload axle seals and goober up brakes, ect=think cranking hard through a freeway cloverleaf. Lowering the level helps that and the rear end still has plenty of lube to live.


Wow , too cheap or too stubborn to change the casting process to move the hole down that much . On all future diffs .

Or make better seals .

But , that does make a little sense on previous builds that are still on the road .

God bless
Wyr

 

[Al]

1 mm below bottom of the hole max lol. Considering everyone puts enough til it starts running out the fill hole....

 

[Snoman002]

This has been common for years. In the early 2000's I had a summer job at a quick lube place. Many of the trucks we serviced required a fluid level below the fill hole.

 

[DoubleWasp]

It's to prevent oil foaming, BTW.

 

[Joel_MD]

The big 11.25" AAM rear axle on my Dodge Ram specifies filling it slightly below the fill hole, which seems ridiculous. There is a line cast into the cover, but how are you supposed to see the oil level inside the diff? When I service it I fill until it runs out the hole, and then suck out a few ounces with my Mightyvac brake bleeder. I figure it's close enough.