MTFCA Forum

Is one quart of gear oil the correct amount for a stock 1915 rear end differential?

Yes, that’s the convenient size to buy, quart will do it. If rear axle pumpkin is totally dry.

Just pour in until the fluid reaches 1 1/2” from the bottom of the fill hole. Don’t overfill.

I was wondering that also how much but also what?I am going to rebuild a 15 rear axel later this month. I spent yesterday cleaning and getting the sand ready for sandblasting. I was wondering what’s the best gear oil to put into it I was told once a while back that this was the right stuff. What do you think?

Most use the 600W or similar which is SAE 90-140 rear lube. Not sure ‘bout that sycro lube as to weight, just don’t use too light as the inner Hyatt’s need thicker lube too.

For early pumpkins with the fill hole high up, best tool for level measure is the ‘Jelf Check Wire’

During the last rebuild I filled the axle while it was on the stand, before attaching the torque tube and radius rods. I was able to see the level inside the axle, I know that this does not help if you are refilling with the axle together and in the car but the amounts would be the same. This is a "later" axle with the fill hole/plug below the center line of the axle housing and it took just a little more than a pint of gear lube (1/2 a quart). Where the ring gear is in the bottom of the housing was covered with gear lube and the level was about 3/4" below the fill hole (looking from the inside). The differential had been rotated/turned to make sure that the lube was not just sitting in the bottom of the housing but was also covering all of the moving parts inside.

In the far left, lower corner of the photos above you can see the gear lube sitting on the shelf (next to the can of spray paint kind of hiding behind the cardboard tube from the new drive shaft), one full and unopened bottle and the one that is "half" empty that was used to fill the axle. Again, sorry for the photos, they are the only ones that I have.

Be sure you have a 15 rear axle in your car. Some older cars have later rear axles placed when repairs have been made. The later axles had the fill hole placed lower and you fill those till it is up to the fill hole. You can tell by looking at the plug. It is approximately half way up the housing on the earlier cars and lower by about 1 1/2 inch on the later ones.
Norm

I measured the amount of oil required to fill the pumpkin to 1.5 inches below the fill hole and came up with 20 ounces. I also pre-greased the hyatt bearings before installation. I made a Jelf tool to check levels and it has remained about where it is supposed to be. My rear end runs very quietly using Lubriplate APG 140 that I got from Langs. I'm using modern neoprene axle seals and so far no lube has escaped from the ends of the axle tube. Too much differential lube and lube tends to travel out along the axles.

I would definitely NOT use Sycromesh fluid...
It’s way to thin and has friction modifiers and other additives for manual transmissions.

Did not mean to move in on this thread but I do want to say here that I plan a trip up to Lang’s for some other parts but I will definitely pick up the recommendation made here for rear end fluid.

Thanks for the help!

When returning Henrietta to active service, I checked the diff oil level to determine if it needed topping up because there was so much build up of greasy, dirty muck at each end of the axles that the cast iron brake shoes were clogged. There was no oil to dip! Rather, the pumpkin was filled with grease, so I just put the plug back in and drive on. When I pull the rear axle to rebuild it some time, I will report on what I find. It seems like a good idea to me.

Allan from down under.

Wayne
Some of the answers given here to your original question are ambiguous.
If your 1915 Model actually has a 1915 rear axle the oil filler hole is in a different place (higher) than other Model T's.
Norman Kling alluded to this fact in his post above.
There are photos of the differences in the location of the filler holes in the Model T book by Bruce McCalley.
If you fill a 1915 rear axle to the bottom of the filler hole you will soon have the oil running out the ends of the axle housings making a real mess.
Make sure which type axle housings you have BEFORE you fill the rear axle.
Ron Patterson

I believe the change in location for the filler plug occurred in 1918.

Thank you to all who have replied. My filler hole is in the middle of the pumpkin, and it took approx. 20 oz. to fill to about 1.5 inches below the filler hole, as determine by the "Jelf" gauge.

USA was a little slow for the transition for the lower filler plug, Canada started with the 15/16
as of yet I have not come across the high one on the pumpkin change at that time frame on Canadian T,s

I agree with Joseph M. One pint is plenty (but watch for leaks and check the level often). Far and away the greatest cause of grease leaks at the rear wheels is overfilling the differential.