Advice on underslung/overslung axles and camber

[mark_gober]

It's been a while since I posted, but it's good to be back. I've got a question involving the axles on my pop-up trailer. (I realize this is a boating forum, but the same principles should apply and I consider this forum to a wealth of knowledge). My popup has a slight condition of negative camber. (the top of the wheels lean closer together than the bottom when it's rolling down the road). I initially thought that the axle was bent because it had a slight bow downward to it. After removing the axle and researching it, I came to understand that most axles are prebent to accomodate the weight that they will support when loaded.

The setup when I got in there was that the axle is underslung (the axle sets on top of the leaf springs). My axle bows downward in the middle. After a trip to Northern Tool and some inspection of their prebuilt trailers, all of their underslung axles are upwardly bent in the middle. I began thinking that my axle may have, at some point in it's life before me, been accidently put in upside down. I talked myself out of that, but now I'm back to contemplating it again.

Here's my question. According to my onsite research at Northern, all underslung axles are upwardly bent in the middle. Are overslung axles bent downward in the middle or are ALL axles bent upwardly in the middle? I'm contemplating flipping the axle over and going to an overslung setup. I know that this is generally not advised, but I think I might be correcting the problem and not inducing the problem.

Can anyone give me some advice on this topic? There doesn't seem to be a wealth of knowledge on the internet regarding these precambered axles.

Thanks for your help and as soon as fishing season starts back, I'm sure I'll be posting again.

Mark

 

[mark_gober]

Re: Advice on underslung/overslung axles and camber

bump...surely someone's got some info on this.

 

[Silvertip]

Re: Advice on underslung/overslung axles and camber

It doesn't matter if an axle is overslung or underslung -- both have an upward bend to provide the desired camber. Because the axle generally has spring perches welded to it, you cannot flip an underslung axle into an overslung application and vice versa because it puts the bend downward. The bend always needs to be upward. Any other way and the camber goes the wrong way.

 

[mark_gober]

Re: Advice on underslung/overslung axles and camber

Silvertip,

Thanks for the reply. I believe that what I have is an incorrectly installed axle. The bend on my axle is downward in the middle and the tires kick inward at the top. Even with the perches welded on the axle, what would prevent me from flipping the axle over to see if it corrects the problem? If you look at the plate that the ubolts go through, there is a hole in the middle. Currently, the bolt holding the leaf springs together goes through that hole. But on the other side of the leaf spring, there is a circular nub that would go in that hole.

I've only had this trailer for about a year and it has clearly had some work done on it before. It wouldn't surprise me one bit to find that the axle is installed upside down.

Mark

 

[smokeonthewater]

Re: Advice on underslung/overslung axles and camber

you are correct... soomeone has flipped it.... you can swap it to the other side of the springs or you can pick up another set of spring perches and just flip it where it is....

 

[Silvertip]

Re: Advice on underslung/overslung axles and camber

The circular nub you mention is the head of the center bolt that holds the pack of springs together. If the axle has a hole in it that the center bolt can engage, then you can indeed flip the axle provided the existing perches don't interfere with the "U-bolts". If the axle is not captured by the center bolt it may slide back and forth on the springs regardless how tight the U-bolts are. Lastly -- are you absolutely certain this trailer has not been overloaded thus bending the axle?

 

[jeeperman]

Re: Advice on underslung/overslung axles and camber

It sounds as if a previous owner at some point took the axle out from under the springs and re-installed it on top of the springs. They did not bother to install more spring perches nor drill a new hole for the spring pack's round bolt head.
Perhaps to lower the ride height.
Or........new springs were installed and the installer did not bother to correct the spring center bolt orientation and just kept going with the installation to getter done and out the door of the repair shop.
So I am thinking you can reverse the process. You will need to remove the spring pack center bolt and reinstall it with the round head down then put the axle back up to and over it.

Have you tried to see what another camper like yours is put together??? or emailed asking the manufacturer??

If you pull the u-bolt plate off, you might see evidence where the axle use to be bolted to the bottom of the springs.

 

[mark_gober]

Re: Advice on underslung/overslung axles and camber

Everyone,

Thanks for the replies. I didn't get into too much detail on what brought me to the point of looking at the axle, so I'll give some (hopefully brief) backstory. The trailer had a slight tilt to the passenger side. I measured it and it was 1" lower on that side. When following behind the trailer when it was being towed, you could clearly see the wheels tilting inward at the top. Additionally, from behind, you could clearly see a slight downward bow in the middle of the axle. In preparation for the upcoming camping season, I decided to investigate/correct the problem.

At the commencement of the investigation, I was unaware that axles are often prebent to counter the weight of trailer and naturally assumed the axle had been overloaded and bent. (that would have explained the downward bend and the tires tilting inward at the top) When I removed the axle to look at it, I noticed that the passenger side leaf spring had a broken leaf. It had two leafs and the smaller leaf spring had broken nearly in half. The broken portion was no longer there and that clearly would explain the lower ride height. After removing the springs, the one missing part of the leaf was nearly an inch shorter than the other one when they were flipped over onto the shackle end. (essentially it was flatter)

I purchased a new pair of leaf springs at Northern tool. I had pondered the axle being upside down and started down the road of flipping it over. Halfway through, I talked myself out of it and reinstalled them the way that I had removed them. After installation of the axle, the tires still tilt inward at the top and I'm pretty certain that the axle has been inadvertantly flipped at some point. I've only had the trailer for about two years and its a 1993 model that has clearly had some work done previously. Some of the work appears to have been done by one of those guys who wings it and isn't concerned with the longevity of the fix (lots of homemade 1"x1" shims and silicone).

Anyway, before I undertake the flipping evolution, I'll try to trailor it down the road and snap a photo of the downward bow and the inward tilt. After flipping, I'll re-run the test and post my before/after pics.

 

[mark_gober]

Re: Advice on underslung/overslung axles and camber

Jeeperman/Silvertip,

I just re-read the last two posts you guys posted. Silvertip, on the overloading issue, obviously, I couldn't swear in a court of law that it hasn't been overloaded, but not since I've owned it. I believe that the trailers net weight is around 1600 lbs. We only carry standard camping stuff in it. Even assuming we put in 600 lbs of stuff in there, you'd only be overweight by around 200 lbs. (and I think 600 lbs of stuff would be quite a bit for a popup that completely collapses when travelling)

Jeeperman, I want to make sure you understand my leaf spring/perch situation. The axle has perches welded to it. The leaf springs have a threaded blot and nut in the valley of the perch and a circular nub on the outer bend of the springs. The ubolts pass through a steel plate with four holes for the ubolts and a hole in the middle. Currently, the threaded portion/nut pass through that hole. (the axle passes through the valley of the springs) I'm considering placing the axle on the outside of the leaf springs and seating the circular nub in the hole in the plate.

I apologize for having to clarify as much as I have. I consider myself an expert mechanic, but trailer axles are just not something that I've ever really needed to work on and I wasn't very familiar with until now. I certainly appreciate all the help you guys have been, even though this particular trailer doesn't have a boat on it.

 

[Silvertip]

Re: Advice on underslung/overslung axles and camber

Before you flip this axle, be aware that if the axle is square, you need square "U" bolts and if its round you need the rounded style. You should not swap the two. Also be aware that unless you use spring perches, the axle will put a great deal of point pressure on the spring thus the potential for breakage. Less of a problem with square axles but a greater problem if this is a round axle.

 

[mark_gober]

Re: Advice on underslung/overslung axles and camber

Silvertip,

Thanks. I'm going to use the same U-bolts that it already has (round) and the axle does have spring perches. (Flat surface welded to the round axle). I'll let you know what the end result is. I'm going out of town this weekend and it's supposed to rain early next week so it might be this time next week before that happens. Thanks again for your help.

Mark

 

[jeeperman]

Re: Advice on underslung/overslung axles and camber

Jeeperman/Silvertip,


Jeeperman, I want to make sure you understand my leaf spring/perch situation. The axle has perches welded to it. The leaf springs have a threaded blot and nut in the valley of the perch and a circular nub on the outer bend of the springs. The ubolts pass through a steel plate with four holes for the ubolts and a hole in the middle. Currently, the threaded portion/nut pass through that hole. (the axle passes through the valley of the springs) I'm considering placing the axle on the outside of the leaf springs and seating the circular nub in the hole in the plate.

Usually the axle goes over the circular nub (bolt head) of the spring pack center bolt. And the u-bolt plate goes to the other side of the spring pack.
Your description says both the axle and the u-bolt plate are in the valley of the springs.