Worn rear axle threads

Conaway2

Conaway2

Well-known member
I’m sure this is a common issue - how do you deal with worn rear axle threads ? The rear axle on my car is original, and I can just imagine how many times the axle nut has been removed and tightened. Although the threads aren’t stripped, I’m pretty careful now when I tighten the nut.

At some point, it will be a problem. Is the most obvious repair re-tapping the threads to a slightly smaller size ?

Thanks - Jim
 
Conaway, a good permanent fix would be to have the axle built up and re threaded. A GOOD welding shop should be able to spray the appropriate material on and then re thread your axle. Just make sure they are experienced enough to do it correctly so as not to change the temper of the steel. I am NOT referring to having someone use a wire welder to do the build up, but to have the material thermally sprayed on. Big difference in the amount of heat generated between the two methods.
 
I doubt there is any mechanical bond spray metal that will stand the required torque to the nut.
If you apply any fusion bond metal you are going to draw the heat treat down. This won't hurt anything if done right.
There is a method that works but it requires removing the axle and it requires a welder that can follow instructions. I have done hundreds of these since the 50's so I know it works.

Glass bead the end to clean it completely.
Get some 1/16 Airco 10016D2 arc welding rod and scrub the flux off of several rods with a wire wheel.
Wrap a wet rag around the axle ONLY in the keyway area especially at the upper (big) end. This is where they break most often.
Preheat just the end of the axle to 200 degreesF.
TIG weld the thread area up enough so new threads can be machined. WELD IN SMALL INCREMENTS TO KEEP THE HEAT DOWN. Keep the rag wet. Do not get in a hurry. DO NOT let the taper area turn color.
When done welding, let cool under a blanket.
Machine new thread.
Lap hub to axle with valve lapping compound till you get at least an 90% contact surface.
Clean lapped surface with lacquer thinner or brake cleaner.
Install axle.
Clean lapped surfaces with lacquer thinner or brake cleaner and install hub DRY with new key
and torque new nut to 225 ft. lb. If you can't get the cotter pin hole aligned at 225, PULL MORE till the hole lines up. DO NOT loosen the nut to align the hole.
 
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Yes, a common fix is to rethread to a smaller size.
The nice part about this fix is that it can be done with the axle in the vehicle and should last until you are ready to tackle a full rear-end rebuild.

The original thread was 5/8-18. You can rethread to 9/16-18. The vendors sell the hardened nuts in 9/16-18 size. Just back off on the torque spec slightly once you go to the 9/16 size.

See this video.
https://www.youtube.com/watch?v=lC_zIvb1Yuo&list=PLav-W1BC-Nj-T6al6Pk5bcpNJQdDfO5H8
 
Pete. The torque value of 225 foot pounds seems very high for 5/8-18 axle nut. Maybe a high of 125 foot pounds, usually we torque to 100 foot pounds on a good used axle and then go to the alignment of the cotter pin.
 
Fhane said:
Pete. The torque value of 225 foot pounds seems very high for 5/8-18 axle nut. Maybe a high of 125 foot pounds, usually we torque to 100 foot pounds on a good used axle and then go to the alignment of the cotter pin.
Click to expand...

Recommended max. is 240.
I have never had one that I fixed, strip or break as long as I lapped the hub.
 
1931 flamingo said:
Wait til something happens. JMO
Paul in CT
Click to expand...

Yes, I have turned and threaded to 9/16 Fine. YOu can get the recommended 100ft-lbs without turning it off. (Some go higher on the OEM size, but 100ft-lbs is kind of proof of the pudding in any case - and why push your luck?)

Still, axles are not that hard to find. I have bought four of them in the last year. The most I paid was $15 per shaft.

But of course getting to the point where you can install it is the challenge.

Joe K
 
I re threaded the axle to 9/16 and also made a much longer nut from hex stock that engages more of the axle threads. Just one hole for key adjusted for proper torque by lightly sanding the length of nut. Has worked fine for 6 years.
 
Bob from Northport said:
I don't know where the 225 torque came from. Way too high. 100 lbs and then adjust for the cotter pin
Click to expand...
I would be afraid of stretching the hub where it jambs onto the shaft taper - not to mention the difficulty in getting it off afterwards.

I've often felt that the shaft nut/thread are somewhere between SAE Grade 5 and Grade 8 bolting.

https://www.boltdepot.com/fastener-information/bolts/US-Recommended-Torque.aspx

9/6 Fine: Grade 5 = 91ftlbs - Grade 8 = 129ftlbs

5/8 Fine: Grade 5 = 128ftlbs - Grade 8 = 180ftlbs
Click to expand...
https://www.bayoucitybolt.com/torque-to-bolts.html

Clamp load is typically around 75% of a bolt’s proof load; that is, the highest stress the bolt can accommodate before experiencing plastic deformation. The proof load itself is usually 85% to 95% of a bolt’s yield strength, but the clamp load is significant because it is what ultimately provides the clamping pressure. Once the clamp load is determined, finding the correct torque value for a bolt is one simple calculation away.
T = K x D x P
Where:
K: coefficient of friction (as determined by bolt surface treatments)
Click to expand...
Table there but K for a lubricated situation (recommended) is usually 0.18

And from this the torque table above is calculated.

"Clamp Load" has it's own transference (K) from movement along the taper to actual expansion (stretch) of the hub which like torque is a function of the friction between the two parts.

220ftlbs certainly above the elastic limit for the shaft thread. Your success to this point may be due to your particular torque "K," which is at best "variable."

Joe K
 
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Just wondered what the torque should be put on an AA truck axle nut,way more than 125 ft/lbs I think .

John in Suffolk County England .
 
john charlton said:
Just wondered what the torque should be put on an AA truck axle nut,way more than 125 ft/lbs I think .

John in Suffolk County England .
Click to expand...
7/8-14 castle (A21941) which according to the chart referenced above (I still have a tab open on my computer) is...

7/8 Fine: Grade 5 = 355ftlbs - Grade 8 = 501ftlbs

I myself remember taking off the rear wheels of an AA basketcase which I brought home. My Harbor Freight "Earthquake" 750ftlb capability 1/2 drive impact wrench would not do it. It took borrowing a 3/4 drive impact from work. (So much for "Earthquake." Maybe that only a "strong tremor" in real life?)

A rear wheel puller from work was also necessary - and a 4 pound "mini-sledge hammer." Also the gas-hammer - and some tempsticks (not to go above 400F.)

That AA was "interesting." Found under a barn here in Cow Hampshire it was seriously degraded due to a generation of dis-use. However, in it's day, that truck was heavily used, and heavily maintained. The engine date code dated the truck to February 1930 (i.e. Borg Warner 4 speed and upgraded undercarriage) but the brake drums were cast iron - which was the 1931 Model AA-Model BB "transitional" drum. (told by a "square" cast into the edge of the drum flange.)

The frame of that truck also had been "rendered" (imagine the loading!) but repaired with 3/4" thick "sister plates" and done up VERY nicely. If I didn't already have an AA truck chassis with only 26K original miles, I would have kept it.

Someone put some serious money into that truck during it's life.

Joe K
 
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My book listed 240 for a grade 8 nut and bolt. I use 225 because there have been no failures at that. Most all of my repairs have been to vintage race car axles. FAR MORE stress than any street driven car for a couple of reasons. They have a locked rear end and FAR more hp.

Oh and another thing, I can get lapped hubs off without any sledge hammers or part damage.
 
fhane said:
pete. The torque value of 225 foot pounds seems very high for 5/8-18 axle nut. Maybe a high of 125 foot pounds, usually we torque to 100 foot pounds on a good used axle and then go to the alignment of the cotter pin.
Click to expand...

model a is 100-120 fps
 
On a tapered shaft, never back off the castle nut to the last cotter pin hole. Always tighten to the next cotter pin hole.
 
Pete said:
I doubt there is any mechanical bond spray metal that will stand the required torque to the nut.
If you apply any fusion bond metal you are going to draw the heat treat down. This won't hurt anything if done right.
There is a method that works but it requires removing the axle and it requires a welder that can follow instructions. I have done hundreds of these since the 50's so I know it works.

Glass bead the end to clean it completely.
Get some 1/16 Airco 10016D2 arc welding rod and scrub the flux off of several rods with a wire wheel.
Wrap a wet rag around the axle ONLY in the keyway area especially at the upper (big) end. This is where they break most often.
Preheat just the end of the axle to 200 degreesF.
TIG weld the thread area up enough so new threads can be machined. WELD IN SMALL INCREMENTS TO KEEP THE HEAT DOWN. Keep the rag wet. Do not get in a hurry. DO NOT let the taper area turn color.
When done welding, let cool under a blanket.
Machine new thread.
Lap hub to axle with valve lapping compound till you get at least an 90% contact surface.
Clean lapped surface with lacquer thinner or brake cleaner.
Install axle.
Clean lapped surfaces with lacquer thinner or brake cleaner and install hub DRY with new key
and torque new nut to 225 ft. lb. If you can't get the cotter pin hole aligned at 225, PULL MORE till the hole lines up. DO NOT loosen the nut to align the hole.
Click to expand...


225?? Insane
 
Pete's instruction seem generally spot on - he's welding with material with 100K effective tensile strength (which is probably 80K when the previous 80 percent of yield is considered.) Still, pretty good overlay, probably better than the original.

However, I might not "cut" the thread - the original thread was "rolled." Instructions today for refreshing the thread on the axle generally go to a "thread reformer" of which there are several versions around, and all do not cut thread but rather "mush" it back into dimensional conformance.

Rolled thread tends to be stronger than cut - which is why most grade 8 bolts today incorporate rolled thread. In fact MOST commercial bolts today incorporate rolled thread since that allows selection of a cheaper steel and yet attain the necessary ANSI property as a bolt.

I have "cleaned" up an axle thread using a "little giant" tap & die - a die system which allows adjustment of the die cut. I start out "loose" and cut the minimum amount of thread necessary to get the nut to start - then use the nut to "form" the thread.

NOW I have a clamp-style thread reformer. Much superior and less chance of crossing the thread with the die.

Joe K
 
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