Rear Axle Key

The chamfered end goes towards the center of the car and towards the center of the axle. The chamfer is put there to accommodate the radius in the keyway that was part of the machining process.
 
To add to what nkaminar says about the key: the point is to have the key "totally fill" the space for it in both axle and hub. There are some "short" keys out there being sold that maybe don't fill into that "ramp" area.

Conversely, one wants the key to "not overhang" the key-slots lest they get hung up in the adjacent parts.

This is one of those I almost wish the suppliers provided the key "long" - and you insert and drive the key home, and then cut off the excess. Were it not for the center retaining nut/thread this could be so.

Joe K
 
The axle key transfers all of the engine's and brake system torques in shear, so the keys must be a snug fit in their key-ways.
 

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Bob you are an experianced Model A person,where did you get the theory that the key drives the wheel.

The first Model T s used a key to drive the wheel and had to change to a taper because the key failed.

All my machine tools are driven by a taper, no keys.
 

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john in illinois said:
Bob you are an experianced Model A person,where did you get the theory that the key drives the wheel.

The first Model T s used a key to drive the wheel and had to change to a taper because the key failed.

All my machine tools are driven by a taper, no keys.
Click to expand...

People have been telling him he's wrong for over ten years, repeatedly. Every time someone asks about rear axles, he jumps in to say the key transmits the torque and has to be corrected. I don't think he's gonna change his mind.
 
Of course the $64 question is: Henry obviously saw a need for the key. So what exactly is that need?

There are an awful lot of Bridgeports that have NO key. And an awful lot of Water Pumps that have a key AND a taper.

I think I'm asking a fundamental question that even this Engineer is not quick to answer.

https://en.wikipedia.org/wiki/Coupling discusses comparison between "keyed" shaft couplings and tapered couplings, the taper generally considered stronger because of no removal of material . But what of those that have both?

Joe K
 
Belt and suspenders. The key is a backup. I have worked on cars where the rear axle nut was loose. The keyway and key were all buggered up. 100 foot-pounds on the nut and check at least once a year.
 
I have wondered why the key. I think it is a backup for a loose axle nut. I have bought a model A with loose axle nut and it drove ok. Axlle was ruined.
My Bridgeport is 1943 and there are many better tool holders now.

John
 
If the taper bond fails the key helps to prevent spun damage to the taper, but only for so long as the key is a weaker means of securement. Keys are cheaper and more easily replaced than an axle shaft that has spun out its taper interface with the hub.
 
Lawn mowers, outboard motors, snow blowers. The key plays a much more important role.

Model A’s, torque the axel nut to 100 foot pounds. If hub nut is not properly torqued, key will deform, break, axel will be ruined.

Enjoy
 
If you were to remove both keys, the car would still move if the rear axel is torqued properly. If not Bob’s comment is correct. The axel would start turning inside the hub.

I have broken a key on one of my cars. It would move and than stop. Fortunately, I did not continue driving. When we jacked up the rear end. Drivers side wheel would spin with a drag and than stop until you put more force on it. Did not matter whether car was in or out of gear.

Passenger side would not turn when we put car in gear.

Removed drum and the key was in piece’s. I could just pull the drum off. No need for a puller. It must have been loose.

From than on I check rear axel nuts every year. 100 plus foot pounds.
 
WHN said:
If you were to remove both keys, the car would still move if the rear axel is torqued properly. If not Bob’s comment is correct. The axel would start turning inside the hub.
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The fit of the two tapers also has to be precise. I think that’s the source of a lot of the confusion. 100 years of wear on either component means that even with proper clamping load via the axle nut, the taper may be incapable of transferring torque without the key if the contact isn’t complete.
 
On top of all the other information provided, don't forget that when assembling the hub/drum to the axle and key, everything has to be CLEAN and DRY, no oil or grease.
 
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