The wheels on the bus go - - - - - -

[JimPghPA]

Down the road without the bus.

Just a follow up about the two wheels that came off the port authority bus while it was doing about 55 MPH on a major highway here in the Pittsburgh area about a month ago. That caused two vehicles to swerve to avoid those tires and those vehicles wrecked.

There was a follow up on the news today. It turns out that the problem was that the lug nuts were over tightened. So much so that the lug nuts cracked, and then came loose.

Now they are installing a fluorescent-orange indicator on each individual lug nut after it is tightened. These indicator have a big pointer and they are installed so that the pointers point towards the next lug nut. With these indicators any lug nut that turns will be caught with a simple visual inspection.

So it turns out that over tightening is just as bad as under tightening.

I wonder if the cold winter temperatures had any part in the over torqued lug nuts cracking?

 

[Chris142]

Those nuts are huge! I wonder how yoi could get them so tight that they cracked? Ive never heard of that

 

[JimPghPA]

Probably some kind of power tool.

 

[TooManyWheels]

Originally Posted By: JimPghPA
Down the road without the bus.

Now they are installing a fluorescent-orange indicator on each individual lug nut after it is tightened. These indicator have a big pointer and they are installed so that the pointers point towards the next lug nut. With these indicators any lug nut that turns will be caught with a simple visual inspection.



I've seen those for a while on the local fleet. Knice to know what they are for!

 

[3311]

Originally Posted By: Chris142
Those nuts are huge! I wonder how yoi could get them so tight that they cracked? Ive never heard of that
3/4" or 1" impact at max setting.

 

[Colt45ws]

When I worked for the County down in Vegas, we used 1" guns on big equipment like that. Never torqued, either, just buzzed them on...hmm, they might need to rethink that. OH WELL, nothing I can do about it now.

I kinda wonder if it was constant overtightening that fatigued them to the point they cracked. If they did the same thing we did, they would have been overtorqued probably nearly everytime a wheel was put on.

 

[TooManyWheels]

Is there any indication whether the wheels in this incident were steel or aluminum? I'm thinking I didn't see the pointers on our local fleet until it changed over to aluminum.

 

[Fleetmon]

The pointers are called WheelChecks and they have two benefits. Number 1, naturally, is the ability to see if a nut has moved out of position indicating a possible loose wheel lug and number 2 is the WheelChecks melt at around 250'F which could indicate a dragging brake or brake not working on the other side of the axle.

I use them more for heat detection than anything and if a wheel comes in with melted "checks", it is warning you something is amiss.

Most bus and truck wheels torque at 450 ft lbs.....a large 1" impact with the proper size air hose can put out well over 800 ft lbs of torque. Overtightening causes the stud to stretch and ruins the studs "elasticity" to "spring" back which is what causes torque. However, in my experiences, most bus and trucks also use hub-piloted brake drums which, if not careful when replacing, can cause brake dust and dirt/debris to congregate at the hub-to-drum interface which will cause a false tightening of the nuts which leads to a loose wheel.....once the wheel is loose (talking only a couple of thosands of an inch here but several hundred ft lbs of torque lost)it is only a very short time before the wheel begins breaking studs and coming off.

 

[NateDN10]

I've seen those on local buses. I figured it was for making sure the lugnuts weren't loose. Apparently it's also to make sure they're not too tight!

 

[GMBoy]

Originally Posted By: NateDN10
I've seen those on local buses. I figured it was for making sure the lugnuts weren't loose. Apparently it's also to make sure they're not too tight!


I was confused too as I know it can indicate a loosening lug night...but overtorqued???

 

[eljefino]

They should make the pointer long enough (and strong enough) that it jams against something and keeps the lug from spinning off.

I bet there's been a real stuff-storm in the maintenance garage, and they have people tripping over each other signing off on and checking each other's torque now.

 

[Fleetmon]

The WheelChecks serve no purpose for overtightned lugs and really don't prevent any loosening and/or tightening of the lugs......it's a simple piece of plastic that is slipped over the nut once the lug is torqued.

Yes, I'm sure there is a lot of attention on lugs at the garage right about now. Also, lugs, particularly when used to secure aluminum wheels are required to be re-torqued within a couple of hundred miles. I always left the WheelChecks off the wheel I just changed to remind me it needed to be re-torqued.....the vehicle was logged in the re-torque book and WC's left off until the next day....the fueling staff would make note of the vehicles in the re-torque book and the fact that WC's were missing and segregated from the rest of the herd for action....either the wheel re-torqued or the cause of the missing WC investigated.

 

[SLCraig]

Originally Posted By: Chris142
Those nuts are huge! I wonder how yoi could get them so tight that they cracked? Ive never heard of that


A 1" impact gun could. Those things are pure beast.

 

[mechtech2]

Maybe the lugs were substandard?
All of them cracked from too much tq?
Normally, lugs strip well before any damage like this can occur.

 

[OVERKILL]

Originally Posted By: mechtech2
Maybe the lugs were substandard?
All of them cracked from too much tq?
Normally, lugs strip well before any damage like this can occur.


Maybe they were sourced from China.......

 

[Fleetmon]

It would only take a nut or two loose to begin the process of all loosening until studs start to shear and then a wheel-off occurs.

The bus involved is a transit bus.....transit buses go through MANY more brake jobs than almost any other kind of vehicle. As a result of so many brake jobs, the hubs, with studs, are used many times over therefore studs may in fact be many years old and had many, many lug nuts tightened over the years. In other words, in the transit world, hubs do not stay with any particular vehicle since with transit, most are the same. I've been there and done it and some of our hubs were 20-30 years old. Yeah, studs were replaced as necessary but Meritor prefers the hubs be replaced if more than two studs are replaced. Most people notice too when replacing studs in these hubs that the hub can actually "grow" a bit which will cause problems when mounting the drum. IIRC, the tolerance of the drum-to-hub was only about 0.012" maximum.....if all ten studs were replaced and each stud caused the hub to "grow" 0.0015", the hub will already be way out of tolerance. The drum may fit over the hub but it WILL crack sooner rather than later from heat-cycling.

There are always a bunch of theories why wheel-offs occur but MOST times the cause is found to be the wheels were improperly installed....either inadequate torque, excessive torque which previously weakened the stud, or dirt/debris between the mating surfaces. I've seen managers question how a bus operator could not tell their wheels were loose and, well....let"s just say that statement is a lot easier to say than it is to live by. The wheels on a bus are approximately 20' away from the driver who is negotiating traffic on a noisey, probably overcrowded bus, operating in the curb lane of some nasty city streets.....the drivers are lucky they have time to inhale/exhale let alone trying to figure out if something is wrong. Let's face it, the average speed of a city bus is normally in the single digits.

OVERK1LL has a good point too.....they could have been inferior studs....transit properties are SUPPOSED to purchase certified replacement parts if the bus operations is in any way funded federally. But we all know how that goes.....a stud is just a stud, right?

 

[JimPghPA]

That bus was doing about 55 MPH. From what I remember I think it was on the stretch of highway by the greater Pittsburgh Airport. On that road there is a long section where the speed limit is 65.

What is really scary is the thought of cars dodging those wheels. I do not know it they went into opposing traffic, but if they did the combined speed and those wheel hitting a windshield are a scary though. From what it showed on the news the wheels in the opposing traffic might of been what happened.

 

[George7941]

We had a few wheel-off incidents in Ontario in the late nineties and a few car drivers were killed by the flying wheels. The government introduced new regulations on how wheels were to be mounted on trucks. Torque wrench use was made mandatory and, as a result, there were no more slamming on the lug nuts with 1in impacts. The regulations greatly reduced the number of wheel-offs.

 

[meep]

i saw a wheel-off in person years ago. car in front of me dropped to the ground and started spewing sparks. the wheel just kept going, on its merry way... took a high bounce in the median and caved in the front left corner/suspension of a large sedan (volvo?) on the other side of the road. that car immediately spun and had secondary impacts. it's been over 20 years.... I don't think anyone was injured, but I noted that had it hit a windshield... the driver would have been killed.

 

[abycat]

alot of big trucks around here have the little indicators on the nuts. I used a 1" impact that was rated to 2400 ft-lbs last year. It was huge.