Drivetrain Failures - Dump Trucks

[KBasson]

Good Day All

I would really appreciate any comments with regards the following issue. I am currently experiencing a high incidence of drivetrain related failures on one of our mining operations in South Africa. I have noticed that we are also overloading our trucks by up to 20%. I would appreciate any comments as to what you believe the expected or anticipated consequence of these actions could be with specific reference to the drivetrain. My colleagues are of the opinion that the overloading could not cause or contribute to the failures. I obviously disagree with this. Any comments will be highly appreciated.

Regards
Kenneth M Basson

 

[GregLocock]

Do your drivers shift from reverse to forward, or vice versa, at full throttle? I've always though that rather alarming practice might have something to do with driveline failures. Overloading teh truck will allow more grip at the tyre, so it may increase the shock loads in the driveline.

I don't know how you escape workplace safety liability issues if you routinely overload the truck, since the manufacturer can just walk away from ANY responsibility.

Cheers

Greg Locock

 

[enginebob]

By driveline do you mean uninversal joints? Or something else? I agree with Gregg. Sounds like a driver problem.
Are they power shift transmissions? Are there alot of hills - grades?

 

[crysta1c1ear]

Are they unloading by reversing backwards until they bump the pile they are trying to add stuff to?

I don't know anything about dumper trucks really, but I'm just trying to imagine one with the back tipped and some stuff not coming off, like having a tractor bring a trailer load of wood for the fire in winter ...

My garage is a bit tight. Tilting is limited when partially reversed-in due to the height of the garage doors. So the farmer can try to jiggle things off the trailer by going up, down, up, down with it; or they can try to-ing and fro-ing using momentum to get the wood to slide out of the trailer.

Accelerating and leaving the wood behind shouldn't be a problem.

But reversing to give the wood momentum and then stopping suddenly could be problematic. If they reverse a bit and hit the clutch and brakes (in that order), I guess that is alright. However a misjudgement of where the pile is would happen every now and then, reversing until things hit a sudden stop.

The other guys here are the experts, but wouldn't reversing into something solid be a massive shock to the driveline.
Is anything like that happening?

When the truck is 20% overloaded, can it still tilt its load properly to unload it, or does that mean it struggles to tilt and they drive backwards with the thing partially tilted until they hit the pile they are unloading into, causing the stuff to slide off and add nicely onto the pile?

=

Just thoughts. I've little experience but you can just bin the idea if its not applicable!

=

Just corrected some spelling and thought more about it. If you try to unload something sticking in the back by accelerating away, you need to be close to 'the pile you are adding to' or else the new stuff will be too far away. So in all cases, you are likely to reverse into things.

Are your guys under lots of pressure to do things quickly rather than well? (Sorry, hard question that one!)

Is your load something that is likely to STICK in the back, like several awkwardly shaped big boulders, rather than something that would come out easily like a pile of chippings? That might mean that the load actually gets stuck and they need to reverse into something to provide enough momentum to shake it free.

Sorry. I'm stuck on this one idea, and your problem could be anything!

Take a ride in one of the trucks and see if you can spot what might be giving the shocks. If productivity drops while your their, they are treating the truck well due to your presence. You need to avoid that somehow.

 

[crysta1c1ear]

*while your THERE - not - while your THEIR.
I've got in IQ of 10 today!

 

[GraviMan]

Hi KBasson,

"I have noticed that we are also overloading our trucks by up to 20%."

That would be the reason then! Off-highway transmissions are designed for a fatigue life based on rim-pull. Since they spend a lot of time accelerating in low gear, 20% overload means that you have exceeded the fatigue stress of ALL the driveline components. It's only a matter of time before the weakest link gives...

On highway spends very little of it's time at full torque in low gear, so fatigue life is based on diffirent parameters. You cannot really compare the two duty cycles.
Most european on highway trucks, for example, would be spitting out gears after their first day on the average road in China (I've actually seen this).

Another favourite mode of failure is overspeeding. Since off-highway trucks are generally used in rough conditions that limit speed, they are seldom are able to "top out". With a very flat dry site, higher speeds can be obtained than even the manufacturer intended. I have even known engine RPM limits to be ignored! It is even worse when trucks are travelling in convoy, since the aerodynamic resistance per truck goes down (cyclists use the same trick, when bunching up).

Put an overloaded convoy on a smooth site, with a slight downhill gradient, and you have a recipe that will upset the hardiest of warranty inspectors...

Hope this helps.

Mart

 

[BillPSU]

What kind of a drive is it and where is it failing?

I worked for Steiger Tractor and when they built a fifth wheel model it was determined the planetary spindle was inadequate. It was determined that the maximum load on the spindle occurred when the load was roaded. The flexing of the tires and the gooseneck scraper was dynamically loading the spindles to higher loads then when digging.

Roading is the worst conditions for highly loaded axles.

 

[Rob45]

Kenneth:
What sort of driveline failures are you experiencing?
In the sort of truck you no doubt have, a 20% overloading is probably not all that uncommon, and might not be at all the reason for your failures.

Are the failures in the universal joints? What type failure is it? For example, brinelling of the joint bearing surfaces might indicate that there's not enough working angle of the joint.

Or are you seeing catastrophic shaft failures? That could be caused by exceeding the shaft critical speed with loaded trucks running downhill, when the design maximum shaft speed could be exceeded.

Need more information!

 

[rmw]

If you are twisting the driveshaft (USA terminology) out of the vehicles, it is designed to be the weakest link, and to give way before something like a transmission, clutch, or differential gives way.

What driveline series are you using??

rmw

 

[IRstuff]

Cannot imagine that the design margin is so tight that 20% over-limits would cause anything but a much longer-term degradation of lifetime.

Even it were that tight, then even "normal" usage would cause premature failures.

Either:
> A bad batch of something
> Poor quality in general
> Some usage condition that's much more severe than 120% of load limit

TTFN

 

[GraviMan]

"Cannot imagine that the design margin is so tight that 20% over-limits would cause anything but a much longer-term degradation of lifetime."

If the truck is operating a lot of the time in low gear, 20% overload will SIGNIFICANTLY reduce lifetime. This could be due to the regular acceleration required on a site, or mudplugging - each site is different. Remember it is rimpull we are considering here, not engine torque.

The transmission (eg ZF or Allison auto) will have a torque converter, that will need to be used more. Most likely the transmission is also being cooked, especially if fitted with a retarder, so that the oil no longer lubricates effectively. Brakes and ALL driveline component lives will be badly effected too.

For offroad stuff carrying, say, 40 tons MAX payload the margin really is this tight! I have actually seen a 100 ton truck overloaded to such an extent that the frame failed! That's why there is a maximum payload specified!

Mart

 

[GraviMan]

Forgot to mention that all the axles have a maximum load capacity too. If you regularly exceed this, you may as well put sand in the axles, for the damage that will occur as the bearings break up.

Overloading ANY off-Road truck really is a very bad idea, unless you want to go into the scrap metal business...

Mart

 

[rmw]

Most axles have their maximum weight rating based on a "road" speed, which these vehicles may or may not reach.

Notwithstanding that, any axle has only a certain amount of maximum "beam" strength, which is not speed dependent. Remember what the civil engineers say, 'if it doesn't deflect, it breaks.'

Off road trucks are regularily overloaded. since they don't have to be subject to the highway weight laws, or cross scales or check points.

I have seen a lot of it.

I would also be surprised at automatic transmissions in this type environment, and would be concerned about how low the granny gear was in these rigs if manual gearboxes. Heck of a potential torque multiplication, if it is like a double low granny.

Bad for drive shafts, and bad for thrust bearings on differential input pinion shafts.

Lots of mines have serious uphill and or downhill slopes, which, if there is a serious (loaded) downhill involved, and there is any serious retardation, such as electromagnetics, hydraulics, or even engine braking, no more powerful than it is, in the lower gears, the torque can be multiplied through the transmission, and whatever form it is, it works on the wrong end of the pinion shaft with respect to the thrust (normally for input torque) bearing direction.

So, Kbasson has driveline failures??

I wish Kbasson would come back on, and give us some more information.

rmw

 

[carnage1]

I am assuming this is a manual trans based on the application you specified
another thing to consider is the engine is not putting out a steady torque, it pulsates and if you are lugging the engine and pushing for max torque at the same time those pulsations rip through the entire drivetrain doing some very interesting things. for example smashing the torque springs in the clutch plate till they break or are too short to do anything, or in the case of dodge diesels warping the splines on the input shaft and the fifth gear (which makes the nut back off and the gear fall out)
so if the drivers are lugging these motors around with the truck already 20% overloaded then I would blame both.