Spring Over Axle (SOA) trailer conversion

joshuabardwell · Aug 22, 2012

I am really tempted to do an SOA conversion on my trailer. The trailer rides low enough that I have to have a really long shank on my WD head in order to get the trailer to ride level. Even worse, the spring bars scrape on the ground sometimes, if I go over a bump or a dip. The extra 4-6" or so would really make a difference, I think.

I have researched the topic extensively, in large part right here on TBN. My axles have camber, so I will need to have new spring perches welded on the top of the axle. I'm really torn on whether to proceed. Mostly, I'm concerned that I'm going to end up messing up my trailer's alignment and wear out my tires, or cause the trailer to pull badly. I guess what I'm looking for is input as to whether this kind of thing is fairly robust, or whether it is fairly sensitive. If I eyeball the location of the perches directly across from the existing ones, and eyeball them parallel, is it likely to be good enough? Once the trailer is assembled, do I need to confirm the alignment, or is it pretty much likely to be good to go? Will the existing spring mounts force the alignment to be correct, for example?

I have read that you can't re-use U-bolts, because the threads won't re-tension right. I've also read some people express concerns about weakening an axle by doing welds on it because the metal is supposedly relatively thin. Any validity to these concerns?

Thanks!

Newblue · Aug 22, 2012

Dexter makes a kit that uses studs and long nuts to square up the axle perches and it comes with new u-bolts. The u-bolts hold the perches to the axle but I welded mine on anyway. This was on my old camper with 3500lb axles.

joshuabardwell · Aug 22, 2012

I'm familiar with that kit, although I didn't realize that it was self-aligning like that. That's cool. I thought you were supposed to weld the perches anyway, though. The etrailer FAQ on the product seems to indicate so. Can you confirm that welding isn't required per, I don't know, the instructions in the kit or whatever? If so, the cost of the kit might balance out the cost of not having to weld the perches on.

joshuabardwell · Aug 22, 2012

Nevermind. With a little Googling, I found the instruction sheet. It looks like they strongly recommend, but do not require, tack welding the perches.

http://pl.b5z.net/i/u/6149609/f/059_551_00.pdf

Diamondpilot · Aug 22, 2012

I have done it a few times to customers trailers and always did the welding. As for the u bolts use a torque wrench and retorque after lowering the trailer and with a load on it. Torque them again with load at 50 then 500 miles.

Chris

joshuabardwell · Nov 8, 2012

Well, I'm going ahead with it. Here are some photos.

I put jack stands behind the back of the trailer...

Then raised the front of the trailer with the loader...

And set a cinderblock under the jack. Currently, the tires are removed and the U-bolts are off. The conversion kits should come via UPS tomorrow (Friday).

joshuabardwell · Nov 8, 2012

In case I decide to go ahead with the tack welds on the perches, what is the typical wall thickness of a 3500 lb axle? Diameter is 2 3/8".

bcp · Nov 8, 2012

Some wall thickness measurements here:

Trailer Axles

Bruce

radioman · Nov 8, 2012

wow-- your trailer looks identical to mine. I'll be watching this thread for sure- its just that I dont have the problem you say you have on yours.

CurlyDave · Nov 8, 2012

I would seriously think about putting something a lot more substantial than that cinderblock under the trailer jack.

If you are really into concrete, a solid pier block would be a lot stronger in compression. Even stacked 2x lumber is better than a cinderblock.

joshuabardwell · Nov 8, 2012

CurlyDave said:
I would seriously think about putting something a lot more substantial than that cinderblock under the trailer jack. If you are really into concrete, a solid pier block would be a lot stronger in compression. Even stacked 2x lumber is better than a cinderblock.

I'm not into concrete much. Just what I had around. You think it's going to crumble?

EDIT: I went out and shuffled things around a bit. I realized that, now that the wheels are off, I can do the rest of the work with the front of the trailer resting on the jack. I set the jack in a little "saucer" that I have to keep it from moving, and then I put a cinderblock underneath the A-frame on either side where it meets the front of the trailer, for additional stability. Most of the weight of the trailer is on the jack, though. Just barely resting on the cinderblocks.

It's really amazing how much the trailer will wobble side to side now that it's off its wheels. Those frames have a LOT of flex in them. Amazing that it can safely take 7000 lbs down the road at 65 mph.

joshuabardwell · Nov 8, 2012

bcp said:
Some wall thickness measurements here: Trailer Axles

Bruce

Thanks, Bruce. They appear to all be 3/16" until you get up to 7000 lbs.

Pops15 · Nov 9, 2012

Throw those cement (they haven't used cinders in them in most of our lifetimes)blocks away and get a set of quality jack stands before someone gets hurt or killed.
By all means weld the perches on.
I don't know why you couldn't re-use the U-bolts. I've re-used many of them on cars, trucks and on a few trailers too over the years.

joshuabardwell · Nov 9, 2012

Pops15 said:
Throw those cement (they haven't used cinders in them in most of our lifetimes)blocks away and get a set of quality jack stands before someone gets hurt or killed.
By all means weld the perches on.
I don't know why you couldn't re-use the U-bolts. I've re-used many of them on cars, trucks and on a few trailers too over the years.

I have jack stands under the rear of the trailer, but I only have two. Anyway, the trailer is now on its front jack, with cinderblocks just to keep the front from wobbling side to side, and jack stands on the rear, so I think it's pretty good now.

joshuabardwell · Nov 9, 2012

A little more work done today. For those who were concerned about my use of cinderblocks to hold up the front of the trailer, here is the new arrangement:

Note that the trailer is actually resting on the jack stand, and the cinderblocks are just stabilizing the trailer from wobbling. On the back (not pictured) are jack stands, as there should be.

One spring has been disconnected, to move the axle. Before I did this work, I disconnected all the brake wires so I could pull the axle out from under the trailer if I needed to. Unfortunately, the wire runs through the dang axle to the other side, and the brakes on this side are spliced off of it. In other words, unless I want to cut and splice the wire or re-run the wire through the axle, The axle is going to stay right where it is until the job is done. I really have no idea how they threaded the brake line through the axle, unless they removed the hubs or something.

Both axles are removed and the springs have been reinstalled.

Here are the new spring perches provided in the Dexter kit. They're basically just standard spring perches with bolts welded to them--literally. Bolt heads and everything. Not even, like, all-thread. The one on the right has the threaded spacers installed. These spacers butt up against the existing spring perch on the other side of the axle, to transfer load to it, since this one will not be securely welded on. These threaded spacers are the "magic" that allows the kit to work without having to weld the new perches to the axle.

Here, you can see the new spring perch on top and the old one on bottom. The spacers must be adjusted so that the new perch is within 1/32" of parallel with the old one, and so that the new perch is tight against the axle. This was easier to do than it might seem like it would be.

Now that I see how it all goes together, I have a better sense of why tack-welding the new perches in place might be good. There is nothing except the pressure of the U-bolt holding the perch in place against the axle. There's no way that the perch is going to come out, but it's not out of the question that the perch could slide laterally against the axle. I dunno. The manual says, "strongly recommend" the welds, but the lazy man in me says, "Ahh come on. Surely the U-bolts will squish it all together nice and secure." What do y'all think?

I am actually attending a welding workshop tomorrow, so I put off the question of whether I'm going to weld them or not until after I get back. No way would I trust myself to weld on new perches, but if all I was doing was tacking it on to keep it from sliding, I might give that a go. I'd still rather save myself the trouble if I could, though.

joshuabardwell · Nov 13, 2012

I got some time to do some more work on this project today. Reconnecting the axle required lifting it into position and then installing the U-bolts. This was hard to do by hand, so I propped the axle in place using a wheel chock as the final spacer.

Then I hand-tightened the nuts, ensuring approximately the same number of threads on each nut.

Finally, I used a torque wrench to finish the tightening of the nuts (no photo of that part).

A funny side-note. I had just convinced myself that I was confident enough to do the "optional-but-strongly-recommended" tack welds on the spring perches, and spent a little while practicing on scrap with various types of rod and amperage settings to try to dial in what I wanted. When I finished all that, I went to weld the trailer, and realized the fatal flaw in my plan: my welder's 6' power cord and 10' leads wouldn't get me over to where the axle was. And I had no interest in cutting the wiring and moving the axles. So I just skipped it. Perhaps an extension cord for my welder should be on my shopping list!

joshuabardwell · Nov 13, 2012

I just got done putting the wheels back on by flashlight. No photo since it's dark out at the moment, but I show that I gained about 5" of height. Should be enough to keep my torsion bars from scraping and keep me riding level!

Diamondpilot · Nov 14, 2012

joshuabardwell said:
I just got done putting the wheels back on by flashlight. No photo since it's dark out at the moment, but I show that I gained about 5" of height. Should be enough to keep my torsion bars from scraping and keep me riding level!

How will the load angle be now?

Chris

Dr Dave · Nov 14, 2012

Whats the price on the kit? Does it come with axle stop blocks to prevent overflexing springs, incase trailer was overloaded. You may need to extend the trailer brake wiring also. I would strongly recommend,getting rid of those scotch lock wire connectors, heat shrink butt connectors work much better especially for wires exposed to the elements.

Dave

joshuabardwell · Nov 14, 2012

Dr Dave said:
Whats the price on the kit? Does it come with axle stop blocks to prevent overflexing springs, incase trailer was overloaded. You may need to extend the trailer brake wiring also. I would strongly recommend,getting rid of those scotch lock wire connectors, heat shrink butt connectors work much better especially for wires exposed to the elements.

The kit is about $50. Here's a link. It does not come with stop blocks. I actually haven't been able to find any of those anywhere, but I may not be searching for the right thing. The brake wiring had enough play not to need to be extended, thankfully. In fact, it had a bit of extra wire zip-tied up out of the way, so I just cut the zip-tie and was fine. As for the scotch-lock connectors, I know their reputation, but there are so many of them that I would basically have to rewire the whole trailer to get rid of them, so I think I will just wait for them to start failing and then take it as it comes.