MTFCA Forum

My rear axle is finally back together. What Ford says is a three hour job has been in the works since October but hey! I'm having fun and learning a lot.

It will soon be time to fill the differential - The question is, with what and how much? I've already purchased some Lubriplate APG 140 and will probably use that - However:
The Ford Service book from the 1920's says to add a pound and a half of "high grade gear compound"

Murray Fahnestock (also 1920's) says a pint (approx 1 lb) of 600 w is plenty - to use more risks sending it out the axles and over your wheels

The Chaffin pamphlet from the MTFCA says to add one quart of 600 w

Your comments?

Tim,

One quart of 600w has always worked for me!

All the Best,

Hank

Tim, you're likely to get lots of different opinions on which weights to use, and probably all of them will be correct. I personally use the 600w and keep it about 1-1/2 inches below the filler hole, or close to level with the bottom of the axle tube.

Stock Ford rear axle, (non-Ruckstell) should have the pumpkin filled 1/3rd full, with a semi-fluid gear oil, 600W is my choice.
Like to fill just below the port, a 1/2" or so below.

If new fill, dry and empty rear axle, check again in 100 miles as the lube will distribute in the innards and that may allow a bit more to be added.

It also has to do with where on the housing is the fill plug - sometime in '18 - '19, the fill plug was lowered to 1 & 3/4" below the housing centerline so fill accordingly to your particular housing. If you have the earlier housing, the level should be at least 1" below the filler hole.

I use 140wt. Lubriplate myself in my non Ruckstell rear axles - 90wt. in my Ruckstells - all 4 of them !

I have always used 600 weight oil in the past. Since I found Henrietta has a back axle full of grease, I may change my routine. This may not be good in a Ruckstell.

Allan from down under.

My filler hole is on the centerline otherwise I could just fill the pumpkin until fluid starts to run out. I made a dipstick and marked it to show a level 1.5 inches below the hole.... I just don't know how much fluid it will take to reach that level. Time to experiment

My understanding is that 140 gear oil has a consistency similar to 600 w oil. Is there any reason to choose one over the other?

Tim, as far as I know you are correct in your belief that straight 140 mineral gear oil is the same as the 600 the vendors sell. The difficulty is finding stockists of straight 140 gear oil. Like most stuff today, they are making oils with multiple viscosities for different conditions, and reducing inventories. It is easy to order 600 from our vendors.
My next rebuild will be packed with grease, just to see how it goes.

Allan from down under.

A fellow with a lot of experience shared with me that it was only necessary to add enough oil to the differential to cover the teeth of the ring gear. Any more tends to result in leaks. (see photo)

I decided to experiment by adding straight mineral oil and looking thru the opening in the front of the pumpkin so see the level. I found that 20 ounces (1.25 pints) was enough to cover the teeth and ride high enough that the hub of the differential just touches the oil. It is well below the opening to the axles which should help prevent leaks. Using my homemade dipstick I measured the oil level at 1.5 inches below the fill hole which I've been told is where you want it to be. Note: My fill hole is on the centerline.

I suspect that after use some of the oil will be distributed into the hyatt bearings and other mechanisms and a little more oil may need to be added. Nonetheless, I think 20 ounces is a real good starting point. Note: This is just my opinion - time will tell the story.

In the 20s there was differential grease available for Ford cars. A compound is a mixture of two or more parts. My personal opinion only I use 1.5 lbs of grade #1 or #1.5 non flowing grease as determined by the NLGI National Lubricating Grease Institute. The treaded plug is for inserting grease and is referred to as a grease plug. The plugs are all in different places on the housing as it doesn't matter when inserting grease. To fill with oil to within a certain level relative to the plug hole is all things to all people as it may be 1 pint or 3 pints depending where it is located. The ultimate default is oil will appear at the axle ends as they were not sealed for oil, felt does not stop anything except some dust from the outside in. Still learning to post photos.