Drop axles - inverting.

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Re: Drop axles - inverting.

Postby mdk » Sat Mar 10, 2012 5:51 pm

KCStudly wrote:I think Angib hit the nail on the head when he suggested that spring wrap will be an issue. IMO it doesn’t really matter what the axle rate vs. load is when you are looking at a dynamic situation like hitting a pot hole.

Look at it another way. When the drop is installed as intended gravity is always trying to stabilize the axle’s rotation and therefore the spring will remain stable. If you flip the axle gravity will always be trying to torque the spring one way or the other, back and forth with every little, and not so little undulation in the road, resulting in many more cycles of fatigue. Depending on the dynamics of this effect it is quite possible that one end of the axle will be attempting to do the opposite of the other end, more so than in the standard configuration, and that could also result in a whole lot of cyclic loading on the axle tube itself...or could set up some wonky side to side oscillations based on minor wheel base changes (as the spring wraps it will change the relative location of the axle).

Don’t take offense, but the fact that you did not realize that the axle spring perches are welded to the axle tube shows that you are not especially knowledgeable on this subject. You may want to reconsider your confidence level at making critical decisions that might affect your and other’s well being.

Take the hubs and brakes off of your old axle(s); buy compatible bare straight axle(s) (gaining 3 inches) with spring perches factory welded in a “spring over” configuration (gaining another 3+ inches); install your existing brakes and hubs on the new axles, and stuff them under your trailer. It’s what I would do in your situation. (I’m a professional mechanical engineer and designer, if that makes any difference to you.)


As to whether the the spring wrap is an issue... It is and it isn't. Millions upon millions of pickup tricks are driving around with anywhere from no to 6 inch blocks between the spring and axle. Yes, axle wrap is an issue, it has its effects on handling, drive shaft geometry, and other matters, but the springs control it, and the number of springs that bust up because of there being blocks is minimal - after all, my truck has 3 inch blocks from the factory.

As to whether the saddles are welded to the round axle... I said I didn't see any welding. I can't imagine they aren't, but I DID NOT SEE ANY. This is not a matter of me being ignorant of how it should be done. It's a matter of looking, but not seeing any evidence of them being welded. Yes, I could have missed it. I have my doubts. I suspect that they actually were not, based on the idea that the axle would be ok without it and gravity would return it to upright if it slipped. It isn't parked at my house it's a few miles away, so I haven't been back to look again, this time up close and in detail.
5 out of 4 people are bad at math.
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Re: Drop axles - inverting.

Postby ebutler » Sat Mar 10, 2012 6:31 pm

angib wrote:
mdk wrote:No, the camber does not improve the towing. The camber is there to make the tires wear better on a crowned road.

I agree that is the 'common knowledge', but I'm going to hold off on believing that until I've seen some engineering evidence. Positive camber has been used on axles since horse-drawn days to improve straight-line running.

Negative camber is valuable/essential on low-aspect-ratio tyres on a racetrack and because of that it has become fashionable elsewhere - I don't doubt it would improve the ultimate lateral grip of a trailer, but that's not what we're after most of the time.


What he said. Makes the trailer follow the tow vehicle better.
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Re: Drop axles - inverting.

Postby KCStudly » Sat Mar 10, 2012 8:54 pm

I apologize for having misinterpreted your comment about the welds, and again, no offense was intended. :oops: :frightened: :worship:

It's so difficult to tell what a person's knowledge base is from a few short words.

You asked for input. It is physically doable, but I wouldn't.
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Re: Drop axles - inverting.

Postby mdk » Sat Mar 10, 2012 11:27 pm

KCStudly wrote:I apologize for having misinterpreted your comment about the welds, and again, no offense was intended. :oops: :frightened: :worship:

It's so difficult to tell what a person's knowledge base is from a few short words.

You asked for input. It is physically doable, but I wouldn't.


I'm considering pulling the frame and axles up against a curb and tugging real hard to see what happens, after flipping. Or something like that. Nothing like testing a theory, eh :thinking:
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Re: Drop axles - inverting.

Postby KCStudly » Sun Mar 11, 2012 12:05 am

I'd be more concerned about the dynamic situations going over the road.

If you do decided to invert (I assume for thrifty reasons) then you should definitely make sure those spring perches are welded on (which we both know they must be/probably already are), and the curb test would at least be like a quality control check before hitting the road.

We had the two rear mono leafs on Mr. B (pumpkin chunkin catapult) fail last year down in Jersey somewhere. It was inconvenient but not catastrophic. Mr. B is equipped with full size tractor trailer landing gear front and rear, we had a support vehicle loaded with tools and capable of running for parts, so we were able to get back on the road in about three hours after finding and installing replacement springs. The fact that we were able to pull off at a good old fashioned gas/repair station and hire the services of their cutting torch made removal of the old u-bolts go a little quicker (although we could have fired off the generator and used the cutoff wheel and 4 inch grinder). My point being that bad things can happen without resulting in disaster, just inconvenience.
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Re: Drop axles - inverting.

Postby skersfan » Sun Mar 11, 2012 2:22 pm

Actually a lot of people do it out here on their toy haulers, due to traveling in sand in the desert.

I have a42 foot fifth wheel that we reversed the axles, placed them below the spring, and basically they tacked welded the axle afer changing the perches.

If the axle is straight you should not have any problems.

I use dexter torflex axles on my off road trailers and I can order them with a drop of 45 degrees, basically a 6 inch raise of the trailer. Talk with a Dexter dealer in your area, they will be able to help you. Or take it to a good RV dealer that does repairs, they can look at it and tell you yes or no. I did it to my 5th wheel and it actually gave me more gas mileage as it raised the trailer to nearly level with my dually. Plus it looks mean!!!
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Re: Drop axles - inverting.

Postby KCStudly » Sun Mar 11, 2012 7:03 pm

In the original post he stated that they are solid axles with fixed 3 inch drop spindles. He wants to flip the axles so that the drop spindles are upside down and the axle tube camber is reversed.
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Re: Drop axles - inverting.

Postby skersfan » Mon Mar 12, 2012 2:21 am

Sorry I missed that. I doubt that it can be done, but I would check with a good RV shop that does lots of repairs. We have one in Banning, local and they are fantastic, very knowledgeable.
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Re: Drop axles - inverting.

Postby Martiangod » Mon Mar 12, 2012 8:23 am

I'd never do it in my our shop, the liability is way to high.
An axel flipped like that is just waiting to be in the ditch with its feet in the air
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