Rear axle nut torque setting.

[stevemclark]

I found the 100ft lbs. on a site claiming it to be a Ford specification although I have read that in the factory there were no torque wrenches there. Anybody heard else this?

[Phil Brown]

Found this on the web for what it's worth
Although the torque wrench was invented in 1918, it didn’t really spread until about 1938 when Chrysler developed the beam torque wrench and licensed it to a small company to manufacture. This company, now Sturtevant Richmont, was incorporated in 1940 and made huge innovations in the torque industry. The beam type torque wrench was perfected and was the primary torque wrench for a while, however as we have seen with many other tools like the hammer and screwdriver, the torque wrench has undergone many changes and many variations have come from that.
Kinda sounds like it might have just got the "thats tight torque"

[alexiskai]

I went back through the archives of The Restorer to look for references to torque values for the rear axle nut. It actually doesn't get mentioned until 1991. There is a Tech Q&A column in which John Hargrave gives 80 ft-lbs as the ideal value, in response to a letter complaining about worn axle keys.

Previous mentions of the rear axle nuts say they should be "tight" or "snug."

[Model "A" Fords]

Morse taper drills and reamers hold the torque with no fastener. The tool is slid in the taper using a quick hand thrust and works as long as the variables are correct. Tapers must be defect free or can produce a poor fit leaving the tool to depend on the tang if there is one. The taper is further tightened by the pressure caused from tool use and requires a drift to remove it. There are many twisted tangs on tools that had poor engagement because of a damaged taper surface.

The axel isn't loaded with a force from one end like above but from multiple directions, some pulling the taper apart. It has to be a nice fit using the nut to keep it engaged and a key for additional safety.

A loose fastener can expand and contract with the load causing fatigue. If too tight it can be over stressed and break. Designed correctly, the fastener will be torqued and pre-stretch to a point where the load during use stays below that set amount to reduce fatigue.

Of coarse what to do becomes a chore dealing with vintage parts with no history, hence the varied recommendations here using the trial and error method which appears apparently largely successful.

[Phil Brown]

Model "A"Fords, well said and 100% agree

[rotorwrench]

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The small tapered shafts I worked with are on magneto drives. The large ones were for propellers and cooling fans on the Robinson helicopters. The fan on the R44 has a BIG taper. I had to purchase a 600 ft/lbs torque wrench since the big nut is torqued to well over 300 ft/lbs. They lock it with a roll pin safetied with .032" safety wire.

The first series Lycoming 0-435 6-cylinder engine has a taper for the propeller on the crankshaft. They don't make the cranks any more but they still require a pretty good torque for the prop hub if a person is still running those old WWII vintage engines.

[redmodelt]

They didn't need torque wrenches. The length of the wrench sets the torque. The main bolt wrench is 12 inches long. An average man pulling on it, can get approx 80 fps of torque to full stop. I don't have a Model A parts book so can't look at the factory axle nut wrench but think it might be longer than that. The factory Model T rear axle nut wrench was 20" long.

[goodcar]

Use the red book spec of 125 if you want to strip the threads.

[Pete]

When I come here, I don't need to watch Tom and Jerry.