The hidden danger of metal fatigue!

Submitted: Saturday, Jan 24, 2015 at 20:42
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Travelling up the highway we witnessed a early model Van with a wheel off, a big furrow ploughed up the road, as we went passed it was clear a stub axle had sheared off,as they had the wheel sitting up with the stub sticking out. this van was a early tandem so they were lucky it just dropped and stayed half straight. At a guess I would say it was late seventys model so getting on in years. To me it looked like fatigue was the cause, as no other vehicles where around, It happened to me in a old truck one time,with a front stub, So its something to be wary of when using old gear.


Cheers Axle
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Reply By: Bushranger1 - Saturday, Jan 24, 2015 at 21:14

Saturday, Jan 24, 2015 at 21:14
G'day Axle,
That should be a reminder to everyone to check under the chassis of vehicles & vans regularly. In particular when driving for hours a day on corrugations.

I found stress cracks on the chassis of my old camper trailer near the spring attachments during my weekly checks on a big trip & got it repaired & reinforced well before it let go.
Doesn't take long to do & its a good time to hose the underbody in order to check it out properly.
cheers
Stu
AnswerID: 544821

Follow Up By: Axle - Saturday, Jan 24, 2015 at 21:44

Saturday, Jan 24, 2015 at 21:44
Mate its one time when the old theory" Out of site out of mind" thing gets a bit dangerous.
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Follow Up By: Ron N - Sunday, Jan 25, 2015 at 00:48

Sunday, Jan 25, 2015 at 00:48
Here's a good one. A mate with a Falcon headed to the East around 1983 from Perth. It was mid-Summer and the Easterlies were strong, as per normal for that time of year.

Halfway across the Long Paddock, on one of the longest loneliest stretches, he spots some score marks in the bitumen.
They're on the LHS of the road, inline with with his LHS wheels.

They waver back and forth and continue on for many kms. He ponders what could have caused them. Something dragging on the road, for sure.

He keeps driving for numerous more kms, and sees a fair-size caravan ahead. As he gets closer (it's not going real fast, about 70kmh), he realises it's on a bit of a tilt to the left.
As he gets up behind it, he sees the back LHS wheel and hub of this fair-sized tandem caravan is gone - completely!! The end of the axle is dragging on the bitumen!

He passes the rig pulling the 'van (a Landcruiser wagon) and waving and gesticulating and pointing and carrying on like a pork chop, he finally makes the driver realise something is wrong, and he pulls up.

The driver gets out, and he's an old bloke - 83, to be precise, as he shortly found out!
He tells him he's short of a wheel and the old bloke looks surprised. "Gee, I thought it was pulling a bit heavy, but I thought it was the headwind!", he says!

They go around the back to inspect the damage - and get this.
The old bloke had been pulling the 'van for so long, with the wheel missing - that the hub had fallen off - the end of the axle had ground along the bitumen for so long, it had lost about 200mm off the end of the axle - and the axle had heated up to red heat - so much so, that the spring had collapsed with the heat, and was now in a reversed camber to normal!!

My mate couldn't believe it, that the old bloke hadn't noticed anything wrong, or had even pulled up to check!
He was of the opinion the old bloke was past towing caravans, and probably past driving long distances, too!

I know some people who are around that age and they are quite fit and healthy - but towing big 'vans long distances is certainly something I won't be doing, when I'm 83!!

Cheers, Ron.
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Reply By: Kev J - Saturday, Jan 24, 2015 at 21:29

Saturday, Jan 24, 2015 at 21:29
G'day guys
Not only old campers, I live near the Gibb River rd and the amount of new Chinese built campers on the scrap heap up here was incredible. Kev
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Follow Up By: Axle - Saturday, Jan 24, 2015 at 21:50

Saturday, Jan 24, 2015 at 21:50
The steel they use is not that welder friendly either, so repairs are a pain so I believe.

Axle.
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Follow Up By: Member - bbuzz (NSW) - Saturday, Jan 24, 2015 at 21:54

Saturday, Jan 24, 2015 at 21:54
It happened to me on a tandem boat.
I put it down to the twisting of the tandem setup when reversing and turning sharp corners.
Too much stress on the end of the axle.
Good practice is to replace axles, on single axles too, after a suitable time interval or mileage.

bill
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Reply By: Ron N - Saturday, Jan 24, 2015 at 22:15

Saturday, Jan 24, 2015 at 22:15
Axle fatigue resulting in fracture near the spring is pretty rare.
It's usually because too small an axle size has been used for the loading.
A lot of people are using 45mm axles when they really should have 50mm axles.
Most axle breaks are at the machined radius at the inner edge of the inner bearing race, because this is a high-stress area.

Cheers, Ron.
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Follow Up By: Steve in Kakadu - Sunday, Jan 25, 2015 at 14:42

Sunday, Jan 25, 2015 at 14:42
There are those that use Landcruiser wheels on a holden/ford bearing, then expect the stub axle to hold up.
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Reply By: 671 - Sunday, Jan 25, 2015 at 00:15

Sunday, Jan 25, 2015 at 00:15
There is also the problem of leaf springs with no shock absorbers. I noticed Collyn Rivers in his article "Why wheels fall off " found while testing suspensions back in his days as a General Motors research engineer that a compressed undampened spring generates 35 times more force than a properly dampened one. This rams the wheel back into the ground with tremendous force inducing excessive stress into the end of the axle and the wheel bearings.
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Follow Up By: Honky - Sunday, Jan 25, 2015 at 13:52

Sunday, Jan 25, 2015 at 13:52
My simple brain would say the opposite. A shock would give the energy of the spring a short sharp jolt i.e. to stop the rebounding of the springs.
In my way of thinking the purpose of the shock is mainly handling and stop you from getting seasick;
One of the main reason I got a leaf spring trailer without shocks was the stories I heard of off road camper vans punching the shock mounting through the sub from on serious off road.

Honky
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Follow Up By: 671 - Monday, Jan 26, 2015 at 00:27

Monday, Jan 26, 2015 at 00:27
They absorb the energy in the spring and dissipate it in the form of heat. Without them there is nothing to restrain a compressed spring when it lets go except whatever is between it and the road. That is where the axle, bearings and wheel stud problems come from.

As Collyn said in that article: the question of why so many caravans and trailers have wheel and axle problems while the cars towing them don't has been asked since the early days of motoring. The answer is cars have a correctly matched set of springs and shocks while the vast majority of trailers leave a lot to be desired.

The first thing I was taught about shocks at TAFE was their primary purpose was to keep the wheel in contact with the road. The wheel will bounce with worn shocks or no shocks.

Shock mounts punching holes in anything is simply poor design. Once again car shocks don't do it although I have seen a few damaged shock mounts and two cases of the rear mounts ripped out of the floor of a station wagon.

All of those cars had aftermarket 'sports" shocks that were far too stiff for the standard mounts.
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Follow Up By: Member - Bill13 - Monday, Jan 26, 2015 at 09:59

Monday, Jan 26, 2015 at 09:59
Honky,
I agree with you 100%. I have towed my Roadstar Trackvan with tandem 7 leaf springs (no shockies) over many dirt roads and just come back from a trip in 2014 that included approx 9000k of dirt. Had this van since 2005 and had no issues with the suspension other than regular maintenance. I let the tyres down to 20lb cold on the dirt and let the tyres help with the work.
No wrecked cupboards or any issues with the van.
Common sense and ground speed along with regular walkarounds plays a big part in it as well when travelling on corrugated dirt roads.
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Follow Up By: 671 - Monday, Jan 26, 2015 at 17:30

Monday, Jan 26, 2015 at 17:30
Member - Bill13 posted:

I have towed my Roadstar Trackvan with tandem 7 leaf springs (no shockies) over many dirt roads.

Had this van since 2005 and had no issues with the suspension.
-----------------------------------------------------------------------

Are you sure you are going to get the same results the next time you go out?
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Follow Up By: Honky - Monday, Jan 26, 2015 at 18:14

Monday, Jan 26, 2015 at 18:14
My Australian built off road camper tailer with 9 leaf springs in addition to 2 "W" shaped leaf on each end ( no shocks) sits better on the road than any of the towing vehicles that I have used which are Pajero, Delica, Commodore, Triton and now a ranger.
I have had friends follow me and they have remarked on how well it tracks.
Never had an egg break in the fridge and these are in an ordinary egg carton.

Honky
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Follow Up By: Member - Bill13 - Monday, Jan 26, 2015 at 20:52

Monday, Jan 26, 2015 at 20:52
671 replied
Are you sure you are going to get the same results the next time you go out?

No one is 100% sure there will be no issues with their suspension when they travel corrugated dirt roads.
However if you are going to travel these remote outback roads then you are a fool if you do not do preventive maintenance on your van and vehicle. Nothing is a given but by doing all that is possible you stand a good chance of not having a mechanical failure.
I have stopped and tried to help good name vans who have broken their simplicity suspension, one to mind was on the Gibb River road. Nothing against the van but caused perhaps by lack of respect on the road travelled as he had past me 2 days previous doing approx 80 Klm on very rough road. Lack of maintenance may also have contributed.
Since coming back from the trip last year, the van now has 4 new springs fitted along with freshly packed wheel bearings. I believe they had reached their used by date. Ready to go on the next trip.
I don't preach to know what is right or wrong but this works for me, so yes 671, I expect the same results next time I travel, along with the next trip after that.
Been working for me since 2005.

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Follow Up By: 671 - Monday, Jan 26, 2015 at 21:11

Monday, Jan 26, 2015 at 21:11
"Since coming back from the trip last year, the van now has 4 new springs fitted along with freshly packed wheel bearings."
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Sounds good but did you get the ends of your axles and your wheel studs checked for excessive stress by a metallurgist?

Using shocks and springs together is not my idea. It has been known to the motor industry since the Model T days when they started using crude friction shocks.

The industry solved the problems of axle and wheel failures way back then but the trailer industry still has a long way to go.

Do the research yourself.
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Follow Up By: Member - Bill13 - Monday, Jan 26, 2015 at 21:55

Monday, Jan 26, 2015 at 21:55
671
I am happy with what I am doing. End of debate.
Take a chill pill mate. All good.
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Reply By: Member - Odog - Sunday, Jan 25, 2015 at 14:38

Sunday, Jan 25, 2015 at 14:38
G'day all
Wife and I have a cub regal off road, we purchased it off someone we know, when I checked under neath, the top shock mounts had been ripped off, and small damage, to the underside of the floor, where the shock had rubbed... We were told the original owner had done the damage, when he purchased the trailer, it didn't have the shocks, we have used the camper, numerous times, and have towed it on one trip of over 10000km.. Coped plenty of reasonably rough tracks, and towed like a dream, although we did get it air bourne a couple of times, driver error, was to blame.. But handled all extremly well. Shocks or not, it seems to tow fine... I don't belive this to be fatigue, more that the shocks didn't allow the correct amount of travel, or maybe , not driving to the conditions.. This is a 2004 model, the damage would have occurred in the first year or two...
Cheers Odog
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Reply By: disco driver - Sunday, Jan 25, 2015 at 15:52

Sunday, Jan 25, 2015 at 15:52
A lot of the time the trouble can be traced back to lack of care and maintenance.
The caravan/boat trailer sits in the shed/yard for some time, someone decides to go for a trip taking the van or boat with them and lo and behold the wheel falls off, bearings, hub and all.

It is particularly noticeable in WA where almost everyone has a tinny or bigger trailered boat. While we are just going to the nearest boatramp and back we have no problems but come Easter or School holidays we all decide to tow our boats from Perth north to Coral Bay, Exmouth and further north or else we head south to Margarer River, Albany or Esperance. In most cases the wheel falls off after about 250km when the hub runs hot because the grease hasn't been checked
or changed since you bought the trailer, if then.

As a preventative measure I decided a good few years ago that the hubs on all my 3 trailers/1 caravan would be cleaned and refilled as close as possible to April 1 each year.

Needless to say I've never lost a wheel in all the years I've been driving.

Disco.
AnswerID: 544846

Follow Up By: Ron N - Sunday, Jan 25, 2015 at 17:58

Sunday, Jan 25, 2015 at 17:58
That's good stuff, Disco - pity more people don't have the same attitude towards trailer bearing maintenance.

Water gets in behind the inner seal or through the bearing cap (if it still has caps! - seen more than a few without them!) and when the trailer or 'van sits for a while, rust starts on the exposed bearing surfaces.
Once you get rust on bearing rollers or races, they fail rapidly.

Used to have to do the old Holden front wheel bearings religiously after every flood event, or even wet Winters when the creeks rose pretty high.

Park the old ute and leave it for a couple of weeks, and you would be guaranteed to hear front wheel bearing rumble within a week or two of taking her out again.

Cheers, Ron.
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Follow Up By: Frank P (NSW) - Sunday, Jan 25, 2015 at 18:47

Sunday, Jan 25, 2015 at 18:47
There's a whole discussion to be had about bearing seals and caps for trailers whose hubs are going to go in the water!

A hot hub that gets immersed will develope quite a strong vacuum that will try to suck water in past the seals and/or caps.

Ordinary seals which caravan and trailer accessory shops refer to as Holden or Falcon seals will hold grease in and under most circumstances, dirt and splashed water out. But they won't hold water out if immersed and there's a vacuum in the hub.

When will that occur?

A braked boat trailer driven through the suburbs in traffic may well have hot hubs on arrival at the ramp. Ditto the off-road camper that's done a long descent down to a water crossing. It takes ages for the hubs to cool sufficiently, far longer than people are prepared to wait, so into the water they go.

A vacuum builds up, even with unsealed bearing caps, and the standard bearing seals simply let the water past and into the hubs.

What is needed for hubs doing this kind of duty are marine seals and sealed bearing caps. The bearing caps must be sealed. As the hubs heat up under braking pressure develops. The marine seals let the pressure out (but they don't let the grease out, just the air) which ensures the bearing caps don't pop off. Then as the hubs are immersed a vacuum develops. The sealed bearing caps cannot leak, which makes the marine seals get sucked harder into contact with the hub, increasing their seal.

For hubs that are going to be immersed, sealed caps and marine seals are the only way to go, I reckon.


There is another option - a very robust type of industrial/agricultural seal. However it will not allow pressure relief, so you have to make sure neither it nor the bearing cap can be dislodged by pressure build-up in a hot hub.

There are bearing caps that give pressure and vacuum relief, such as this one, available in common sizes:


Cheers
FrankP

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