Rear axle nut torque setting.

RHD

RHD

Well-known member
What is the required rear axle nut torque setting? There must be a torque setting these days. Usually I just go good and tight, but would like to adjust properly and have both rear nuts the same.
 
You're gong to get as many answers to that as if you asked which oil!
I do mine to 100 ftlb ± but don't get fussy because it will change when you line up the holes for the split pin.
 
My method (the brake adjusting board was a handy length)

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100 ft-pounds is a good number. Do that and then tighten more to line up the cotter pin (split pin). Do not loosen to line up the cotter pin. Check the torque after a short amount of miles, about 100, then again every 6 months or a year thereafter depending on how much you drive your car. The key does not keep the hub from moving. It is only a secondary backup. The taper on the axle is what keeps the hub from shifting on the axle. You can use some Loctite on the axle if you want. Do not drive the car with a loose nut.
 
In my opinion and practice since 1962, I find 50 lbs-ft works without causing deformation of the tapered hub. 100 lbs-ft of torque is too much. These slides explain my logic and practice:
 

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Tapered shafts always depend on condition of the tapers. They also had to be clean and dry with a key that fits properly.

Torquing them is a process more than just a one time deal. They should retorqued several times after a period of operation down the road. When they stop moving during follow up torque application then they are seated about as good as they get.

For many years, folks have been using torque values based on the diameter and thread type of the screw fastener being torqued. A person has to have some proven methods to go by when torquing screw thread type fasteners. When a cotter pin safety is part of the mix then that also has to be taken into account. A 5/8" X 18 tpi thread can take a lot of torque even if grade 5. SAE charts put the dry torque over 100 Ft/Lbs for grade 5. If the threads are in poor condition or stretched to make the nut hard to turn then adjust the torque to prevent failure. If threads are lubricated then torque is less.
 
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It does not matter. Pick a number between 40 and 100 that you are comfortable with and use it.
The chances are, it will come loose before it should (never) are very good.
Not one person in 100 ever installs the rear hubs as the factory did so how can you expect them to never come loose.
The factory installed them with at least 95% bearing surface on the taper (machined). That was as good as the machinery of the day could do. You can only do better by grinding or lapping the surfaces.
If you lap the hub to the axle and are able to get 100%, it will run with NO key and never come loose, IF all of the threads are in good condition and it is torqued to proper spec according to the SAE charts.
Almost no one does that.
 
The amount of torque does matter because it stresses the hub significantly. Basing the amount of torque on the thread size is not a wise practice. An engineer bases the amount of torque on the stresses in the joint design. The "Red Book" advises torques on the basis of an SAE chart which pays no attention to the joint design. Keep in mind that there were no torque wrenches used in the original build of the Model "A."
 
I will keep torquing mine to 200 as I have done since the 50's.
I have NEVER had one come loose or broken an axle, EVEN ON A VINTAGE RACE CAR.
Oh, and my engines make over 300 hp.
 
My procedure is to set my torque wrench at 90 ft. lbs. then tighten until it clicks. Then look to see where the cotter pin hole is. If it is in view, I leave it. If it is not, I tighten slightly more until it is.

If there is not sufficient toque on the rear axle nuts the brake drum can rotate against the axle key each time you brake and accelerate. This constant pounding against the key slot in the axle can allow a crack to start at the inboard end of the slot. Over time it will work its way around the circumference and the wheel will come off as you are rolling down the road.

Each time I rebuild a rear end I examine the axle key slots carefully and if there is a slight crack, I advise the customer to have the axle replaced.

Tom Endy
 
Tom, I know the cracks you refer to but have a very different take on how they start. From my experience, if the hub moves back and forth as you describe, a crack will open up along side the keyway and a chunk of axle will come off yet it will still drive. The crack that results in the wheel parting company, IMO are due to worn rear wheel bearings. As we know, the bearing surface in the hub wears at the axle nut end. That means that end is larger and with the wheel supporting the weight of the car further out on the axle, the axle is being bent by the sloping wheel. The wheel is inclined inwards at the top as a result of the taper and as it rotates, the stresses in the axle change with every turn. Compression one moment and tension the next. That, repeated over and over many thousands of times becomes too much for the tired old axle and it breaks. The end of the keyway is the obvious place for the crack to develop.
For the longevity of the axles, the rear wheel bearings MUST be in good condition.
 
Anything I have been told says the taper to taper drives the wheel not the key. The key is there just in case. 50 is not enough.
 
The subject of rear axle nut torque never fails to generate interesting discussions. Is it the fit of taper or is it the key that conducts the torque. I believe that it's both. Case in point, take a Morse taper drill shank for example, it like the Ford axle has a taper angle that is designed as a "locking taper" and in fact it will lock and successfully transmit a limited amount of torque, however Morse taper drill shanks ALSO have a flat shank end that fits into a socket that absolutely prevents any slippage.... a two-part system, just like the Ford taper and key. How much torque on the nut? still up for discussion, I suppose. My opinion, something less that 100ft-lb
Joe B
 
I give up arguing this topic. I will continue tightening the nuts to 50 lbs-ft which I have been doing with success for the past 61years.
 
From Brattons under the top bar,Specifications, includes capacities,clearances torque values and what a raven finish is.FORD MODEL A SPECIFICATIONS Rear Axle Nut 100 ft lbs.
 
One thing I'm curious about, and I don't know whether we have the relevant diagrams available – does the angle of taper on the hub precisely match the angle on the axle, or is it slightly narrower?

I'm wondering if perhaps the purpose of the high clamp load by the axle nut is to force the narrower hub taper outward as it presses onto the axle, which would maximize the surface area engagement between the two tapered surfaces.
 
I'm wondering where the 100 lbs of torque number came from ?
Also on a locking taper, the angles match. I don't think you could torque the nut enough to change the size or shape of the hub ?
 
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