What Gear Lube to use in a Ford Model A

Question:

I'm looking for a gear lube for my 1930 Ford Model A. The Model A suppliers sell lube that is 600W. The container only states it is 600W and no other information is given. I know 600W is not the weight of the lube. It stands for cylinder oil. Mobil makes 600W in several ISO viscosity grades, but which one can be used in the steering box, transmission and rear end? I was thinking on Mobil 600W with an ISO viscosity grade of 680. The lube needs to be thick to slow the trans and slow any leaks. I have been told the lube needs to be safe for copper, brass and bronze.

Do you have any suggestions on what type of lube to buy and where I can get it? The Model A club members would be thankful for any help.

Answer:

There appears to be very little mention in original Model A Ford literature on what should be used in the transmission, but a couple of references do specify 600w gear oil. No one I have been able to talk to knows for sure how they measured gear oil viscosity back then, or exactly what was meant by it. But it is also apparently known as steam oil. Steam engines, contrary to what we might imagine, did need a certain amount of oil in the water from which they made steam.

Modern rough equivalents are Texaco Meropa 680, Shell Omala 680 and Castrol LS 680, and the Mobil 680 you mentioned will do the trick too.

I have heard of people using STP blends with lighter modern gear oils as well, but I would worry about the amount of heat STP can handle without losing its viscosity. As for the type of oil, only mineral-based gear oil is applicable. No vegetable-based or other 600w weight oil is appropriate except perhaps a synthetic exists. I was not able to locate one with any of my sources.

Some Model A owners use heavy modern gear oil such as 250 ISO—and it works— but it may also leak out the rear around the universal joint if that seal is not good, and the transmission will not shift as smoothly. Smooth, quiet operation of the straight-cut gears was the reason for the heavy gear lube in the first place.

Modern oils that contain additives that attack yellow metals such as brass and copper are unacceptable in any case because they can cause bushings and other soft metal parts to deteriorate. To determine if such additives are in any modern equivalent gear oil, call the manufacturer for advice.

Fortunately, though, the original formula, correct gear oil for your needs is available from Snyder’s Antique Auto Parts, among other sources. The part number is M533 and it sells for $7.95 a quart.

Perhaps the easiest way to get the stuff into the differential is to use a squeeze bottle similar to the types they use for mustard and ketchup in diners. You can reach Snyder's at: snydersantiqueauto.com

Another good source for original correct Model A transmission lube is Mac’s Auto Parts. https://www.macsautoparts.com/