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Old 08-17-2002, 10:59 AM   #1
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Wheel Assembly Balancing

Hi, I'm new to the group and wanted to know about the critical procedure for balancing Airstream tires/wheels, then hubs, then tires/wheels AND hubs again, together.

I'm told severe stress and heat buildup to point of failure will occur if balancing procedure is not exactly followed.

Could anyone enlighten me as to if this is correct?

Thanks in advance,

CJ
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Old 08-17-2002, 02:16 PM   #2
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that's what they say,but finding someone too do it is the problem.i just have mine computer balanced
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Old 08-17-2002, 09:44 PM   #3
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HUB/TIRE BALANCING

I think Andy of InlandRV mentioned that if you cant find an RV place that still does it, most TRUCK tire places can do this kind of balancing. Im guessing that is a reference to Heavy Duty Semi truck tire places. Let us know how you make out.
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Old 08-17-2002, 11:08 PM   #4
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Wheel balancing

The interesting thing about this wheel balancing thing is if you brought your trailer to any AS dealer in the country and asked for a wheel/hub balancing they couldnt do it for you because they are not set up for it. If you brought your trailer to the factory and asked they couldnt do it for you either they dont do wheel/hub balancing, so what does that say?

"I'm told severe stress and heat buildup to point of failure will occur if balancing procedure is not exactly followed."
Where/Who did you hear this from?

Check this link http://www.airforums.com/forum...=&threadid=165
and this link
http://www.airforums.com/forum...=&threadid=100

John
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Old 08-18-2002, 09:22 AM   #5
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Awesome, this has gotten to be an urban legend.

On the plus side, balancing the rotating assembly has it all covered. I understand vibration is going to cause damage. But in my world the roads induce more stress than an unbalanced brake drum ever could.

On the side of reality, this seems like over kill. The wheel and tire are balanced as a unit, the only thing left is the brake drum or rotor. To say that it is so poorly cast and machined that it must be balanced or disaster will strike makes me question it's integrity.

John
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Old 08-18-2002, 12:42 PM   #6
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I have checked the drums on my van and on my vintage car for signs of balancing - both have it.
The A/S drums don't.
I am going to ask my friend at a local machine shop if they can balance brake drums.
They do cranks and other engine components, perhaps they can also do drums??
If so, then one can get the drums balanced, so as to get closer to a vibration free assembly. Maybe not perfect, but a lot closer.
This is assuming that a well balanced tire/wheel assembly is being installed.
I can see the point here. Very low axle mass, very high unsprung weight. Disastrous if out of balance ( IF!) in my humble opinion.
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Old 08-18-2002, 08:40 PM   #7
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Airstream says they do not balance the hubs or drums on new units.

But the frame has been beefed up substantially since your '73 came out, so perhaps they no longer need to.

Andy at Inland Rv believes passionately about this. He contends it is the source of the dreaded "tail droop" in the 70's rear bath models. But his is about the last place on the planet where it can be done.

The amplitude of any vibration is going to depend on the moment arm. An out of balance tire is going to cause some pretty terrific vibration. An out of balance drum, being closer to the spindle, will cause less. An out of balance hub less still. Likewise, the longer the trailer, the greater the amount of movement caused by the vibration at the nose and tail. The tail of a 31 foot unit is farther from the axles than a 20 foot unit, and will move up and down far more.

Finally, the greater the weight at the end of the frame, the more damage a given amount of vibration will cause. So a rear bath, with the waste tank(s) located well aft of the axles will suffer more than a side bath.

If you could get someone to balance the drums, it would be a plus. On the other hand, there must be thousands of Airstreams and Argos- (just what IS the plural of Argosy, anyway?) out there that have never had the wheel assembly balanced.

Mark
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Old 08-18-2002, 09:34 PM   #8
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Tail dragger (tail droop)

"Andy at Inland Rv believes passionately about this. He contends it is the source of the dreaded "tail droop" in the 70's rear bath models. But his is about the last place on the planet where it can be done."

The tail droop from rear bath trailers was from the added gray water tanks and putting them in the rear behind th axles, they were not supported enough by the frame and when people travelled with them full it made it even worse. The constant bouncing pulled them away from the trailer. Later AS beefed up the frames and they have kits now that can fix the problem as well.

John
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Old 08-19-2002, 11:29 AM   #9
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John.
Rear end separation did not happen because of the gray tanks.
Trailers made prior to 1974 had the problem. They did not have gray tanks.
The on going confusion comes from owners not understanding what vibration can do to most any object, when there is a moment arm involved.
The moment arm on any Airstream trailer, is the distance from the point of last support to the ground, which is the rear axle, to the rear end.
The moment arm on a 31 foot trailer is 10 feet. Therefore one pound of energy becomes 10 pounds at the rear. Same thing if a bike and rack is added to the rear. Except now the moment arm is about 12 feet. If the bike and rack weighed 100 pounds, then the real weight at the rear becomes 1200 pounds, yes, one thousand two hundred pounds. That is a dead weight. When a bump is hit, then that weight multiples quickly, however momentarily.
Granted, some changes were made in the construction, to beef up the rear end. However, it was not because of inadequate design, but an attempt to overcome the lack of proper running gear balancing, by the owners.
Rear end separation still takes place, and it becomes obvious when that trailer is examined. Poor maintenance.
Ask any pilot about moment arm. They will tell you the difference 10 pounds makes depending on sitting along side of him, or in the tail of any aircraft ever built.
This story has perpetuated itself since the mid sixties and probably will continue to do so.
The question is, if it was such a poor design, then why didn't the separation happen to everyone, instead of the select few?
Hmmmm.
Good discussion material for a rally bull session.


Andy
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Old 08-19-2002, 01:33 PM   #10
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Andy, thank you for enlightening me. I was planning to add a bike rack to the rear of my TT. I think I will find another place to put it.
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Old 08-19-2002, 01:44 PM   #11
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Sorry, Andy, I don't buy it

I'll buy into the fact that speed bumps, curbs, chuck holes, gutters, even the thumps between concrete sections on I-10 may ultimately do rear-end damage because of the moment arm.

I'm sure of the fact that driving with the black tank loaded is almost certain to do damage sooner or later given its location. I will not drive with more than a couple of gallons back there.

What I can't buy is that the low amplitude vibration of a spindle with a properly balanced wheel and tire is going to cause rear end separation or any other major damage. The suspension and the massive intetia of the trailer is going to damp out that level of vibration, especially with 4 or 6 spindles at random vibration phases.

I just had my wheels balanced this morning. My intention was mainly to insure tire life; the trailer is already smooth enough that I towed 150 miles a couple of weeks ago with a ring of keys laying on the dinette. They were still there when I stopped..
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Old 08-19-2002, 01:52 PM   #12
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"When a bump is hit, then that weight multiples quickly, however momentarily.
Granted, some changes were made in the construction, to beef up the rear end. However, it was not because of inadequate design, but an attempt to overcome the lack of proper running gear balancing, by the owners."



It seems to me you are talking about two things, trying to roll them into one.

The moment arm from vibration should be transferring energy from the wheel/tire/drum outward through the trailer, but the moment arm from the bump in the road will transfer energy from the rear to the point on the frame where the rear spring shackle mounts (admittedly to the point of tire contact on the ground but that is not the failure point). 1200 lbs is conservative when you consider some of the holes in our roads and the speed the hole is hit, i.e. the trailer will still be dropping into the hole, but the axle will already be on the way up. Even with decent springs and shocks this has to be thousands of pounds. This is the type of energy transfer that will cause the frame to bend.

Damage from vibration is usually a different form. If the vibration is the right frquency it could theoritically tear the trailer to pieces in minutes. Realistically it will affect different components at different frequencies. It could fatigue the metal frame to the point of failure, but it should stress an entire rail and require that it be replaced not reinforced. First damage would be to the interior as it is not as strong as the frame and shell, cabinets shaken to pieces, seperated from the walls, etc.

But I still don't understand this. If the tires and wheels are balanced, the only unbalanced part of the rotating mass is the brake drum/hub. The out of balance weight is such a small percentage of the rotating mass, dampened by the shocks and springs. How much energy actually is transmitted to the trailer?

John
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Old 08-19-2002, 02:00 PM   #13
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Good answer 74Argosy

It is obvious that we agree wholeheatredly concerning what will and what will not damage a trailer. and that vibration and impact are not the same thing.

I'm sure Andy is sincere, but I think he is way off base on this one.
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Old 08-19-2002, 04:42 PM   #14
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John. If I am off, then so is the factory. They are the one's that said it many many years ago.
I have nothing to gain by giving out information. You, the owners do.
It is still your choice anytime, any day, to do as you wish.
The real problem, is for our newbee.
Facts are facts. They are not opinions.
To disprove facts, do the research, and then disagree.
Surely using the results of several thousands of examples, I would think, is always better than ones personal experience and opinions.
Just my thoughts based on 36 years of everyday experience.

Andy
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