Why did my axle break?

[jim galli]

In 54 years of using and abusing Model A's I've never experienced a broken axle. So I'm curious what the combined talent here can teach me. Did it break because the rear roller bearing is worn out and it flexed too much? How would someone measure that?

This is a car that gets used. Myself and 2 high school buddies did 1000 miles in this last October. All our gear plus junk we picked up along the way. Some dirt roads. Maybe 5% of the drive. Happily a photographer friend and I had just loaded our 8X10 camera outfits and were heading out for a shoot and the axle failed in the driveway. Pretty good luck, eh? We loaded everthing in the trunk of the '38 coupe and carried on unphased.

Yes, I did search first. Thank you ahead of time for your ideas.

[larrys40]

Jim,
I have had one break as well. I think metal fatigue is probably most likely. I was lucky they line failed in a parking lot albeit 500 miles from home. I changed it out the next morning .
Axle keyway and hub we’re fine . Just it’s time . It broke inside the housing and couldn’t be seen. Many times keyway stress from looseness can contribute near the key slot.

I’ve rebuilt hundreds of axles and che k them for stress cracks. You just don’t know.
Anyway, glad it didn’t happen on the road .
Replace it, check the other side.
All the best
Larry shepard

[Tom Endy]

What I have noticed is that a crack will occur at the inboard end of the locking key. I suspect it is due to the axle nut not being torqued down to 100 ft. lbs. This allows the key to rock fore and aft with acceleration and braking. The crack starts out ever so slight. For this reason I inspect the axle shaft key slots very carefully during a differential overhaul.

Eventually the crack will increase until it travels the full circumference of the shaft, and then separate.

Tom Endy

[M2M]

Originally Posted by Tom Endy

What I have noticed is that a crack will occur at the inboard end of the locking key. I suspect it is due to the axle nut not being torqued down to 100 ft. lbs. This allows the key to rock fore and aft with acceleration and braking. The crack starts out ever so slight. For this reason I inspect the axle shaft key slots very carefully during a differential overhaul.

Eventually the crack will increase until it travels the full circumference of the shaft, and then separate.

Tom Endy

Tom, how do you rate the new axles that are available? Are the axles sold by the various suppliers all from the same source? If no, which ones do you recommend?

[Tom Endy]

I would not buy one. The gear end is welded on and I have seen some that have come apart. I also had one in a job where the gear end was too large. Whoever put it together must have notice it was locked up. However Henry's 40 horses broke it loose and it wallowed out the inside of the carrier. I had to replace the axle and the carrier.

They are also too expensive at about $400. There are plenty of serviceable originals still around. Try Bert's in Denver.

Tom Endy

[M2M]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by Tom Endy

I would not buy one. The gear end is welded on and I have seen some that have come apart. I also had one in a job where the gear end was too large. Whoever put it together must have notice it was locked up. However Henry's 40 horses broke it loose and it wallowed out the inside of the carrier. I had to replace the axle and the carrier.

They are also too expensive at about $400. There are plenty of serviceable originals still around. Try Bert's in Denver.

Tom Endy

The gear is welded on??? I know that new axles for Model Ts have no gears so you need to remove the gears from old axles and fit them to the new ones (by pressing them on I think). Model A axles couldn't have been made the same way? New Model T axles are about $100 each.

[Purdy Swoft]

I've never had a model A axle break .

Here is my thought .

The outer seal that is just past the outer wheel bearing wears a pretty bad groove in the axle .

looking at the pics , it looks like your axle broke in that area

[Mike Peters]

The rear axle broke a year ago on our 28 Tudor. Same place as yours. I think the axle nut was tight, but it still broke. Just check your axle nut torque from time to time and hope for the best. Lots of good used ones around, just check carefully for cracks just behind the keyway.

[SteveB31]

Tom Endy, the welded on axles have not been made for aa couple years. The new axles made now are all one piece and made by the same company that currently makes axles for Ford, and in the USA. $495 each though.....

Steve @ Bert’s

[Synchro909]

Originally Posted by SteveB31

Tom Endy, the welded on axles have not been made for aa couple years. The new axles made now are all one piece and made by the same company that currently makes axles for Ford, and in the USA. $495 each though.....

Steve @ Bert’s

Heck, that would be near enough $1,000 by the time it got here. I only want an axle, not the whole darned fatory!

[M2M]

Originally Posted by SteveB31

Tom Endy, the welded on axles have not been made for aa couple years. The new axles made now are all one piece and made by the same company that currently makes axles for Ford, and in the USA. $495 each though.....
Steve @ Bert’s

Good news; but a pity they don't sell them without the gears (like the Model T ones). Without the gears they would be a lot cheaper.

[Bob Bidonde]

Axle failures like yours are not rare occurrences. This type of failure is the result of fatigue and a stress riser. The photo here is a textbook classic of how a fatigue crack initiates at a stress riser and grows to become a static overload.

The stress riser is at the end of the axle's key slot where the taper begins. Note how the crack grew outward across the section of the axle.

[M2M]

Originally Posted by Bob Bidonde

Axle failures like yours are not rare occurrences. This type of failure is the result of fatigue and a stress riser. The photo here is a textbook classic of how a fatigue crack initiates at a stress riser and grows to become a static overload.

The stress riser is at the end of the axle's key slot where the taper begins. Note how the crack grew outward across the section of the axle.

Would not having rear shocks on a car mean more fatigue and a stress on the axles?

[rotorwrench]

Ford had a lot of time to experiment with different steels to come up with a relatively ductile axle that could take thousands of stop and go cycles. These shafts do twist a bit during every cycle so eventually fatigue will get all of them. The design was such that it had a built in place for failure with the key way being cut in there like that. If the key way had radii cut in, it would have last longer but likely not a great amount of cycles longer. It was a "designed in" weak point. I don't think Ford would have ever thought that so many of these cars would still be on the road 90-years later.

[jim galli]

Thanks so much for all the answers. I'm lucky. It happened at home in the driveway, and I have a parts rear end in the back yard that still has it's drums on. When I get it all dis-assembled I'll do some good pics of the break along with whatever other evidence I can see then.

Yes, it's remarkable that we're running around in these almost 100 years later with so few problems. A testament to good engineering and materials.

[Y-Blockhead]

Originally Posted by Tom Endy

What I have noticed is that a crack will occur at the inboard end of the locking key. I suspect it is due to the axle nut not being torqued down to 100 ft. lbs. This allows the key to rock fore and aft with acceleration and braking. The crack starts out ever so slight. For this reason I inspect the axle shaft key slots very carefully during a differential overhaul.

Eventually the crack will increase until it travels the full circumference of the shaft, and then separate.

Tom Endy

I wonder how many folks are out checking the torque on their axles this morning...

I actually did check mine ~2 weeks ago while doing my "bolt check" routine.

[frank55a]

I had the right axle break on our 29 Tudor coming back from the 86 MARC/MAFCA meet in Wisconsin. We had driven about 3500 miles on that trip and were about 5 miles from home when I went around a sharp corner onto a bridge. It had rained a short time before and the road was dry except for a small puddle about 4 feet in diameter. I was only doing about 10MPH. When the rear right wheel hit the wet spot it spun up and then when it wheel hit the dry pavement it was like trying to bring the wheel to an abrupt stop while the axle was still spinning. It twisted the axle and broke it. Needless to say over the years I have collected a few spare axles just incase. Anyone need an axle contact me.

[ursus]

Originally Posted by Bob Bidonde

Axle failures like yours are not rare occurrences. This type of failure is the result of fatigue and a stress riser. The photo here is a textbook classic of how a fatigue crack initiates at a stress riser and grows to become a static overload.

The stress riser is at the end of the axle's key slot where the taper begins. Note how the crack grew outward across the section of the axle.

I have some axle shafts that are in nice shape except for an annular groove worn into the shaft where it rides in the seal inside the housing. Is this a potential site for breakage or not a concern (aside from oil leagake)?

[ronn]

maybe the HS buddies were doing hole shots, while you were out picking up lunch...........?

[Joe K]

Originally Posted by M2M

Would not having rear shocks on a car mean more fatigue and a stress on the axles?

Hard to say.

Use of shocks may actually INCREASE cyclic loading - best shock restraint is called "critical damping" - a skosh more damping (technical term) results in almost impact, while a skosh less damping can result in wheel hop.

Um - extending this thought, the best (least force on the axle) damping condition MAY be where wheel hop is imminent - and impact is minimized and extended.




Joe K

[jim galli]

Originally Posted by ursus

I have some axle shafts that are in nice shape except for an annular groove worn into the shaft where it rides in the seal inside the housing. Is this a potential site for breakage or not a concern (aside from oil leagake)?

It appears this is the area of the breakage in my case. Groove gets worn and perhaps even a bit more heat at that one spot over 90 years. Maybe this spot becomes the "stress riser"?

Originally Posted by ronn

maybe the HS buddies were doing hole shots, while you were out picking up lunch...........?

I'm more worried about the transmission when they drive than the rear end. Crunch crunch crunch.

Hey, if it only breaks every 90 years, I'm good with it.

[Jim M]

I had one crack and was lucky someone following me tooted and told me my right rear wheel was wobbling. Shure enough when I took it apart there was TWO cracks and would not have lasted long. I took the oppurtunity to take everything off up the the engine while I had it apart. After lots of $'s and 6 months of putzing it is back together and running fine. I got two used axles from Bert's and am VERY satisfied with everything I have got from Steve. He also knows just about everything you ever need to know about the A's and gives great advice!!! Jim

[Tom Endy]

I had a job a while back where the failure mode was the gear end of an original axle shaft sheared where the gear attached to the shaft. There were actually two failure modes. Years before the differential had been overhauled by someone who did not understand carrier pre-load. When the car was back on the road the rear was locked. Henry's 40 horses broke it loose. Usually it does so by spinning the carrier bearings on the mounting hubs. In this case it was locked so tight that it sheared the hub on the ring side of the carrier. The car operated like this for about 8 years before the heat cycling finally got to the axle shaft and the left axle shaft sheared right at the gear next to the sheared carrier hub.

See the attached link for photos.

Tom Endy



http://www.santaanitaas.org/wp-conte...ilure-2018.pdf

[alexiskai]

If I want to check the torque on those axle nuts, do I need to remove the wheel or can I just remove the hub cap? May be a stupid question, but I'm having trouble visualizing it.

[M2M]

Originally Posted by Tom Endy

I had a job a while back where the failure mode was the gear end of an original axle shaft sheared where the gear attached to the shaft. There were actually two failure modes. Years before the differential had been overhauled by someone who did not understand carrier pre-load. When the car was back on the road the rear was locked. Henry's 40 horses broke it loose. Usually it does so by spinning the carrier bearings on the mounting hubs. In this case it was locked so tight that it sheared the hub on the ring side of the carrier. The car operated like this for about 8 years before the heat cycling finally got to the axle shaft and the left axle shaft sheared right at the gear next to the sheared carrier hub.

See the attached link for photos.

Tom Endy

http://www.santaanitaas.org/wp-conte...ilure-2018.pdf

Tom, perhaps you can get a hold of one the new one piece axles Steve from Berts mentioned and let us know what you think.

[Mike Peters]

Sponsored Links (Register now to hide all advertisements)

If I want to check the torque on those axle nuts, do I need to remove the wheel or can I just remove the hub cap? May be a stupid question, but I'm having trouble visualizing it.

Alexi_ There is a cotter pin to remove in order to check axle nut torque. It will be much easier to remove the wheel in order to get the cotter pin out and back in later. If there is no cotter pin in your axle, by all means install new cotter pins.

[Purdy Swoft]

Originally Posted by alexiskai

If I want to check the torque on those axle nuts, do I need to remove the wheel or can I just remove the hub cap? May be a stupid question, but I'm having trouble visualizing it.

I would just remove the hub cap . Removal of the hub cap may require the removal of the wheel to bend back tabs


If you have an extra wheel and tire without a hub cap ,

maybe you could temporarily use it and save having to remove the hub cap on your nice painted wheel .

After the axle nut is retorqued the original wheel can be replaced

The 28-29 hubcaps can sometimes be snapped off like a modern hubcap

[Bob Bidonde]

100 ft-lbs torque on the axle nut is extreme in my opinion as it increase the tensile stress in the axle shaft. Cracks occur in tension stress fields. I run with 50 ft-lbs, and have not had any issues doing so in over 50 years of Model A'ing.

[alexiskai]

Originally Posted by Bob Bidonde

100 ft-lbs torque on the axle nut is extreme in my opinion

Don't the V8 guys torque to 200? 100 doesn't seem extreme in that context.

[ryanheacox]

According to my bolt chart, Grade 5 5/8-18 is good for 170ft-lb dry. Assuming the axle shaft is not quite grade 5 and with 90 years of use and fatigue I definitely wouldn't want to go over 100ft-lb. Last time I did mine I went to 90 and then lined up for the cotter pin.

[Tom Wesenberg]

Originally Posted by ursus

I have some axle shafts that are in nice shape except for an annular groove worn into the shaft where it rides in the seal inside the housing. Is this a potential site for breakage or not a concern (aside from oil leagake)?

Unless that groove was deep and had sharp edges I wouldn't think it will be a problem.
I think worn wheel bearings and axle tube could allow more flex and could be a contributing cause to broken axles.
I'm an easy driver, and have never broken an axle.
Hole shots, and spinning the wheel on mud or ice can certainly snap an axle.

[dumb person]

Originally Posted by alexiskai

Don't the V8 guys torque to 200? 100 doesn't seem extreme in that context.

I don't think they do. Probably 120 max.
200 for a rotary flywheel nut maybe, but you'd pull the axle right through the hub at 200 on a ford.