What a messy job! I just filled the differential on my '26 and it took exactly one quart of 600w gear oil to fill it to even with the bottom of the hole, using a suction gun from Auto Zone. Took me longer to clean up that infernal sticky mess from the floor and myself than it did to fill it. Yuk!!!!
To make it easier to draw it up into the suction gun, I put the 600w oil in a pan of hot water for about 20 minutes. It flows much easier when it is warm.
Thanks John. I'll remember that.
If you buy a suction gun from Auto Zone. unscrew the end and pour the thick oil into the top. When pushing it into the differential, don't get in a hurry. Go slow, as you gently push the oil into the hole, or the thick gear oil will blow back, past the rubber plunger seal and end up on the backside of the plunger and you will get a nasty surprise when you pull the plunger back to refill it and the oil flows out the wrong end. Rarely have I felt so grimy as after that job and the subsequent cleanup. Jim Patrick
It's also easier to remove the oil if you drive the car a short while before trying to remove the oil.
Mine was way too thick for any suction gun to remove so: Removed the spare tire for more room. Spread some plastic on the floor. Put a low pan under the diff. With a 1 gal. plastic bag on my left hand and a 3/8" X 1' dowel in my right proceded to dip and wipe. Actual time to empty the diff was about 2 hrs. over the period of about a week. Got right to the bottom. Turned one wheel about 1/4 turn once in a while for the "drippings". Slow, but clean and easy. Formed a sheet metal channel, U shapped,small at one end for the diff hole and poured the fresh oil in.
Much easier with 140wt lube and good rubber seals instead of the 600wt. I hear ford only used that because it was less likely to flow past the poor leather and felt seals and foul the brakes. True?
The thinner lube is much less hassel to use and seems like it would distibute better to the inner works of the diff. better.
Some old diffs, taken apart, reveal a congealed ball or glob of that 600wt lube caked around the works. Who knows how long that was in there though.
Ruckstell (Chaffins)requires lighter wt lube as they feel the 600 will not flow into the guts well enough as I recall.
Jim, I have been there with the old oil behind the plunger sneak attack...real mess unexpectedly.
My differential was empty from when I took it apart several years ago, so all I needed to do was inject the oil with the suction gun. I guess it can be called an injector 'cause it can be used to suck out the oil, or inject the oil. I understand that prior to 1919, the hole was located precisely at the centerline so that, when filling, one needed to stop about an inch below the bottom of the hole. I believe it was 1919 that Ford lowered the hole about 1.75" below the centerline so that the oil can go right up to the bottom of the hole. I believe a rule of thumb is that precisely 1 quart will be about right for all Model T differentials. if they are all the same size as the 1926, but like just about everything on the 1926, the differential may have been redesigned and/or enlarged to accomodate the extra weight of the improved, all steel body of the 1926. Please chime in if this is wrong. I am only an authority on my 1926, which took exactly one quart. Jim Patrick
My 90-something year-old Model T guru says to put one pound of lube in the rear end. One pound = 16 oz., which = one pint.
I think your 90 year old guru is correct. You only need enough oil for the ring gear to run in. I tried a full qt. and had oil pumping into the wheels. I sucked out about half, and have not had problems since.
Isn't it astonishing how much oil a quart is once it's all over you and the floor?
John Gelfer and I put the oil into my diff this fall. It only needed a pint. Just enough to cover the ring gear. We were lucky that the diff was not in the car yet, so it was easy to pour in with a funnel.
Adam Doleshal also installed a drain at the very bottom so it will be easy to drain when the time comes. He also recommended driving the car to warm it up before draining.
I have not had much success with a suction pump. The way I do it is to take a short piece of drip system tubing. I think it's about 5/8" thinwall plastic tubing used here in our arid area for drip irrigation. I use a funnel in one end and put the other in the hole in the differential and bend the tubing so the funnel is up. Then I pour the oil into the funnel.
If you put in a quart, it will be in your brakes the first time you drive it.
I picked up a large syringe from a veterinarian one day to try. This works extremely well. Just suck it out of the can and inject into the fill hole. About a 5 minute job.