Loose key in rear axle

Richard, nkaminar, the taper on the axle is not a locking taper and cannot be associated with the taper in use on machine tool collets, etc. The taper on the Model A's axle is for centering the axle. Try this. Take the keys out of the axles and run your Model A. You will not get far as the friction of the taper fit cannot react the engines torque, so the drum will spin on the axle. I have done this experiment, so my analysis is not armchair engineering. Ford engineers added the key for a reason, and that is to transmit the engines torque. This is a basic engineering concept.
 
It is a locking taper. If it wasn't you would not need a drum puller or a torch to remove drums that have been properly installed. Larry has it right. Something not mentioned here is the condition of the taper. At this point in time I would suggest most axle and hub tapers have been ruined by amateur mechanics and hobbyist who are unfamiliar with how tapers are supposed work. The proof is in the pudding. Worn keys and keyways get into that condition due to improper assembly, simple as that. The last two model A I purchased the axle nuts where on basically finger tight which is a recipe for disaster. Consider yourself lucky if your axle tapers and keyways are in good shape. I have worked with locking tapers on flywheels and axles since the sixties. If your tapers have ridges and discoloration the hubs have been loose and have lost their functionality.
 
Well...this just upset my barrel of apples. Two totally opposing views from well respected Model A owners/mechanics.

I'm a novice Model A mechanic. What I am well trained at is how to read and remember what I have a passion to know. I've read about this question in many places including online at various rear end and axle articles as well as this and other forums. The best answer I have seen may be that the two components, (the taper and the key) work together.

The coupe I've owned for 4+ years and driven 24,500 miles had scarred axles and hub tapers. The keys were loose in the key way. Last winter I found a long crack that meandered parallel to the axle key from the inner end of the keyway all the way into the threads. I rebuilt the rear end with two good axles (tight key ways) and two new hubs and centered drums. I torque the axle nut to ~95 - 100 lbs. I remove the rear wheels, clean and repack the bearings at 2500 miles. The nuts have never been loose and sometimes pop as they let go (using the vendor's bell shaped hub puller).

I sometimes read Dyke's and the Service bulletins. I seem to remember one of those two advising to: "tighten the axle nut heavily"????
 
Discussion at length about required torque of the rear hub nut at https://www.fordbarn.com/forum/showthread.php?t=288009&showall=1

My comment on 9/16" reduced thread/100ish ft-lb is there. And someone who perhaps indicated 225ft-lbs as "a number" (too high IMHO.)

The problem with too high is you can "stretch" the hub. 5/8 fine thread Grade 8 lists officially as 240ft-lbs which may be true of Grade 8, but the axle is not necessarily Grade 8. Probably more like Grade 6.5 (ha,ha - something better than Grade 5, but NOT Grade 8)

I see my opinion from 2020 has not changed. Not quite into "live for the moment" memory.

https://www.almabolt.com/pages/catalog/bolts/tighteningtorque.htm

Joe K
 
Bob, i suggest you try your test again. You don't have to drive the car, which could be dangerous. Keep one rear wheel on the ground and jack up the opposite side. Remove the key. Clean the hub and axle tapers with acetone so that no oil or grease remain. Torque the nut to 125 foot pounds. Put the transmission in low and then try to turn the wheel. You can try jerking the wheel back and forth which will add the inertia of the wheel and tire to your test. Don't overdo that or you may damage something.
 
Rob has nothing to worry about as he has done things right. My guess is Bobs tapers were not in the best shape and or nuts not tightened enough. As mentioned in the links provided by Joe lapping of the tapers may be needed to affect a proper axle - hub fit. Also of interest in the bolt torque charts is mentioned these torques are for non critical parts. I think I consider wheels failing of as possibly critical! Last thing is torque specs depend a lot on the treatment of the threads. Most specs are for lightly oiled threads, not dry. Also very important but not always considered is whether the bolt or nut is plated or not. I take note that I have never seen a factory axle nut that appears to have been plated but it seems the nuts supplied by vendors is plated which does require a significant reduction of the torque, sometimes as much as 25 per cent.
 
Another thing ! I would have to believe that at the factory workers were supplied with an appropriately sized wrench to affect the proper tightness of whatever nut or bolt they were tightening. In the case of the axle nuts I suspect the tool was of ample size to do that.
 
I couldn't find a photo of the wrench, but I did find a video of a heavy guy putting all his weight on the end of the wrench to tighten the nuts on the rear axle. The guy is in the background and full view is obscured by another man, but he is clearly really snuggling up that nut. I seem to remember a photo of the wrench used in the factory and it was pretty long. The guy tightening the nut was jumping up and down on the wrench. The guy in the foreground is installing the hub and drum on the rear axle.
 

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50Trucking said:
Larry, Have you had any luck in shimming axles that are rubbing the backing plates or the inner side of the drum against the emergency brake band?
Click to expand...

I’m not a fan of the shims unless they are absolutely necessary. The ones from the suppliers are decent, just make sure you fit them and make sure they are curves and not obstructing the key. They can be trimmed easily with sharp scissors. This is to shim it out slightly so the drum doesn’t seat quite as far in. Absolutely only one if needed. Sometimes backing plates have issues so make sure that’s not the case first.
If there are any metallurgic issues with the axle or hub , gauling, loose keys , crack issues, poor threads , replace them .
Loose nuts will not get tighter , only looser.
Wheels do and have come off!


Recapping if you use a shin fit it we’ll install in hub so it has a bit of tension to the hub inside , key on axle and install. Tighten to minimum of 125 ft lbs. with a well fitting nut , and if course cotter keyed at the end . It doesn’t hurt to check your axle torque now and then. Something not thought of often enough.
It actually helps to reduce failures and sometimes uncover issues.
Not saying I have all the answers but I’ve probably done more axle rebuilds and service than most .
Happy A motoring guys !!!
Larry Shepard
 
I agree that the taper is what is doing the job. Ask any machinist about tapers securing cutters on lathes and milling machines.

That being said then why was the key also included? I would guess it is in case the taper did in fact fail to hold?

Seems as like the were designed to work in unison? :confused:
 
If you make and use home made axle shims, DON'T use galvanized sheet metal, use shim stock.
 
The key is there in case the nut gets loose, which they do. But it will get damaged if the nut is loose.
 
Also you can leave your hubcaps off. After driving a 100 miles or more, check the nuts. If the drums and axles are in good shape and the nut was torqued properly the nut may not move but if any of those requirements are not met you can be pretty sure the nut will need tightening. I am old enough to know what was once common mechanical knowledge has now become a mystery to many. To find the root cause of a problem requires more than just a cursory inspection and quick conclusions. Many problems are masked and have several layers that need to be pulled back
 
Richard Knight said:
It is a locking taper. If it wasn't you would not need a drum puller or a torch to remove drums that have been properly installed. Larry has it right. Something not mentioned here is the condition of the taper. At this point in time I would suggest most axle and hub tapers have been ruined by amateur mechanics and hobbyist who are unfamiliar with how tapers are supposed work. The proof is in the pudding. Worn keys and keyways get into that condition due to improper assembly, simple as that. The last two model A I purchased the axle nuts where on basically finger tight which is a recipe for disaster. Consider yourself lucky if your axle tapers and keyways are in good shape. I have worked with locking tapers on flywheels and axles since the sixties. If your tapers have ridges and discoloration the hubs have been loose and have lost their functionality.
Click to expand...
I agree 100% with everything said here, said the machinist of over 50 years.
 
Some have asked about the use/need of a key at all. Since the taper is self-locking?

It might have been created this way as an "assembly convenience" and simply to hold the hub stationary while the hub bolts were fully tightened/torqued.

One might check the previous pix/movie and see if they can tell if the hubs are "held" while the nut is being torqued?

Joe K
 
My local machine shop in England recuts a new keyway 130 degrees away from the original . He says NEVER cut a new keyway 180 degrees away .

John in sunny Chandler AZ but maybe some rain on Friday !!!
 
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