trailer SPRINGS, going over instead of under

[Boeing]

Fellas,
I was fussing last fall about my trailer being so low when I loaded it up with Tractor/loader and bush hog. The rear of the trailer is not more than 5" off the pavement. I called the trailer company who made it and was told that it has 2500# axles and 3 leaf springs.
I just went to Northern Tool and bought 4500# springs (4 leaf) While there they had a "kit" which included brackets for the ends of the springs, bushings, a center bracket, shackels etc. and drawings of the springs ABOVE or BELOW the axle.
HERE is the question guys: My springs are currently UNDER the axle.....WHY can they not be set OVER the axles giving me at least 3" higher ground clearance? There is a metal plate that the springs set in and it is cupped to sit on the round axles.... I don't think it cares if it is above or below the axles. Can anyone advise me here.....am I missing something important? I would like it higher as the road into my property is a bit rough and 5" clearance is going to bottom out a few times...dragging taillights, license tags etc.....not to mention perhaps bringing me to a grinding stop.

 

[Bird]

First, is that metal plate the springs sit in welded to the axle? Some trailer axles and springs are designed so you can put the springs over or under the axle, so some are not I once thought I was going to move springs from below the axles to above them on a travel trailer I owned, but it couldn't be done with that one.

Secondly, you say you have 2500# axles and you bought 4500# springs. How much weight do you put on that trailer? Are your tires, wheels, spindles, bearings, and axle tubes capable of handling the weight. When we had a 32' fifth-wheel trailer with 3500# dual axles, I was running 7,300 pounds on them; a bit overweight. So I went to the manufacturer and asked about doing the same as you; add a leaf to the springs, but I've have still been overloading the other components. What I actually did was replace everything below the frame. We put new 5,200# axles, using axle tube made for 7,000# axles, new wheels, bigger brakes, and new tires.

 

[Verticaltrx]

What you are trying to accomplish is a spring over axle conversion, people have been doing it on 4wd trucks for decades. I have a couple trailers that I have done it on.

I would use the springs that came on the trailer, the others will overload the axles. You will need to purchase another set of weld on spring perches since your axles are probably cambered and therefore cannot simply be turn over. Weld the new perches on top of the axle, move the springs and spring plates above the axle, and bolt it all down using the original u-bolts, that's all there is to it. You will probably gain more like 4-5" of lift instead of the 3" you mentioned.

 

[Raspy]

There is no problem at all moving the springs to above the axles. Just weld on new spring perches and set the axle under the springs.

Your new 4500 lb springs are probably a good idea too. It's not the spring that overloads the axle, it's the weight you put in the trailer. Old springs can sag and even break. So go ahead and use your new ones and place them over the axle, Good plan!

 

[Skyco]

It's not the spring that overloads the axle, it's the weight you put in the trailer.

True for a static load- but for a dynamic load that is not true. The axle capacities must be derated if NO springs are used so I would imagine too stiff springs would also require some derating.
An impact (pothole) could bend the axle that may have been a non issue with properly compliant springs.

I'd return the springs, move the axles under the original springs and either weld on new spring seats or, if they are Dexter axles, they sell a conversion kit that doesn't require welding.

http://i.b5z.net/i/u/1080235/f/Trailer_Height_Adjustment.pdf

 

[rockinmywaypa]

I can't understand why anyone or any company would suspend their load on the u-bolts when the load can be carried and leave the u-bolt to simply hold things together. When I joined a company a few years back there was a lot of grumbling about a particular trailer breaking down a lot, as soon as I saw what the set-up was I suggested they rearrainge the orientation so that the axle carried the springs instead of hanging them, end of problems and a more level trailer to boot.

 

[Raspy]

I can't understand why anyone or any company would suspend their load on the u-bolts when the load can be carried and leave the u-bolt to simply hold things together. When I joined a company a few years back there was a lot of grumbling about a particular trailer breaking down a lot, as soon as I saw what the set-up was I suggested they rearrainge the orientation so that the axle carried the springs instead of hanging them, end of problems and a more level trailer to boot.

I agree. The physics of a "hanging" axle really don't make sense. It's just a compromise for a lower ride height, if that is needed. But a terrible design.

 

[Raspy]

The axle capacities must be derated if NO springs are used so I would imagine too stiff springs would also require some derating.




No springs, is a way different case than stiff springs. I have used 5200 lb springs on 3500 lb axles with no issues at all. None of them ride very well when empty, but that's the nature of a short leaf spring with no shocks. And, old springs can break if they are bent or rusty, or just old. I've had it happen. It's a good idea to replace old springs and the U bolts whenever modifying trailers. Further, if you do overload the trailer at some point, it is less likely to bottom with stiffer springs. Bottoming is a shock load. So, stiffer, in an overloaded situation is less likely to break an axle because it is less likely to bottom with a heavy impact. But it will ride rougher with a medium load.

If you have a travel trailer, you can match the springs to the load fairly well, but then you might go to Baja and pound through hundreds of pot holes. If you haul a tractor, as I do, the trailer gets towed empty at 2000 lbs and loaded at 8000 lbs. It's also easy to take a 2000 lb rated trailer to Home Depot and get a "few" bags of concrete and some tile. Next thing you know you've brought home 4000 lbs of stuff. Always a compromise. But, bottoming is not your friend.

 

[Skyco]

The axle capacities must be derated if NO springs are used so I would imagine too stiff springs would also require some derating.

No springs, is a way different case than stiff springs.

Certainly is. Apparently you missed the key word "some".

Did the OP say anything about bottoming? No- he wasn't looking for more capacity he was looking for more ride height.

Two different problems to solve....stouter springs just to gain height isn't the correct way to do it. My:2cents::drink:

 

[Boeing]

I did it.....now we wait to see what I have caused. I dropped the axles, the springs were already the 4500# 4 leaf....so I DID NOT change them. I DID flip the axles 180 degrees so bottom is UP now. The spring plate WAS welded on the bottom to keep the springs under the axle. I rotated it to the top and now the springs are ABOVE the axles. Put it all back together and the trailer bed is about 5 inches higher than before. I LOVE it. I found all bolts torqued (or rusted) about 120 LBs so I soaked them all in penetrating oil during removal and retorqed them about 20# "tighter than tight". I'm guessing about 100#. I will really like the height when I get to the gravel road in Virginia.
Thanks for the input and advice.

 

[Skyco]

As already mentioned most axles are cambered. Were yours?
If they were you are now cambered the wrong way and will get a lot of tire wear.....if they were truly dead straight axles (rare) you should be good.

 

[Zork]

As already mentioned most axles are cambered. Were yours?
If they were you are now cambered the wrong way and will get a lot of tire wear.....if they were truly dead straight axles (rare) you should be good.

I agree. The trailer may not follow as nice in the turns with this reverse camber. The negative camber helps the tire roll onto the tread in turns rather than rolling off the tread in a positive camber setting.

 

[lostcause]

I can't understand why anyone or any company would suspend their load on the u-bolts when the load can be carried and leave the u-bolt to simply hold things together. When I joined a company a few years back there was a lot of grumbling about a particular trailer breaking down a lot, as soon as I saw what the set-up was I suggested they rearrainge the orientation so that the axle carried the springs instead of hanging them, end of problems and a more level trailer to boot.

bolts are used in tension every day. that's about what it amounts to when you run the axle over the springs - a tension force as the axle tries to lift away from the springs. it's just a matter of designing the diameter of the bolts to compensate. over the years a lot of companies have done it. i know many jeeps have been built that way, because as mentioned earlier, people do axle flips on them to gain more wheel / tire clearance. i also know the 1st gen gm s-trucks had the axle slung over the springs. i'm sure there are a lot of others too. there's no problem in doing it, though you might want to reconsider the little 3/8" u-bolts with the generic mounting kits.

 

[rd_macgregor]

This may be a naive question, but if the axles are cambered and you flip them over AND side to side won't you be back where you started?
Maybe that's not mechanically feasible, but it sounds topologically correct.
BOB

 

[Verticaltrx]

This may be a naive question, but if the axles are cambered and you flip them over AND side to side won't you be back where you started?
Maybe that's not mechanically feasible, but it sounds topologically correct.
BOB

You're thinking of caster, not camber. In this case there is no proper way to do it other than installing new spring perches on top of the axle.

I have a small 4x6 utility trailer that I did a spring over conversion on, at first just by moving the axle without installing new perches. Due to the negative camber in that situation the trailer tracked terrible, swayed side to side and was overall miserable to pull. When I got time I put new spring perches on top of the axle so the wheels have the proper positive camber again and it pulls 100% better. Plus, running an axle with negative camber like that is a good way to permanently bend the axle tube. The camber is also built in the axle tube so it straightens out with a heavy load to prevent bending the axle. With it upside down you are encouraging more bending.

 

[DanD78]

What was the bottom of the axle needs to stay the bottom of the axle due to the arch built in to the axle tube. I see new tires in your future.

Dan

 

[Boeing]

Hmmmm....I'll have to slide under it next time I'm up there. The axle tube sure LOOKED straight as an arrow when I rotated them. The hub (wheel plate?) looked vertical-perpendicular to the mounted wheels visually. It towed GREAT, 903 miles to VA. Then I towed it empty 90 miles to pick up some water tanks and a spreader....and 90 miles back. So far I'm really happy.:thumbsup:

 

[Raspy]

If they are simple straight tube axles, they have no camber problem. You could just rotate the axle tube and bring the perch to the top. Keep the wheels on the same side they were on, so the brakes are not running backwards.

Of course, this won't work with offset spindles and camber bent axle tubes. But it will work with straight axles, and it sounds like that is what you have.

No need to debate this to death and think of everything we can that might go wrong. It's a simple modification.

If the axles do have a camber bend in them, and it's obvious if they do because you can simply look under the trailer and see the center of the axle is bent up, then weld on new perches above the existing ones and don't rotate the axles.

 

[Boeing]

John, you mentioned BRAKES.....so far I have not connected or used any?probably not too smart). What is required to hook up the electric brakes and then....do they work? I had BOAT trailers years ago that all had SURGE hydraulic brakes, they worked fine...especially the newer trailers with DISK brakes. Are Disk brakes available for this equipment type trailer? Is it worth the expense? Thanks for all your input guys.
Rob

 

[Raspy]

Electric brakes work very well and are better than surge brakes because you can apply them independently of the truck's brakes, but they are not good for boat trailers.

They are also cheap to buy and easy to install. Most axles have a flange already welded on the axle to mount the backing plate for each wheel. Then you run a set of two wires to the front of the trailer. These can Y to each rear wheel on an axle or there can be a set of two two wires for each wheel. Probably number 12 minimum size wire.

They feed from the truck through the plug and get the power from a brake controller.

All my trailer have drum brakes. I have a set of 3500 lb axles that will skid the wheels with a trailer GVW of about 7,000 lbs. And I use the brakes in the mountains a lot for stability and holding on grades. I just checked the brakes and they are about 1/2 gone after many thousands of miles. Never had a problem. My other trailers have 5200 lb, 6000 lb, and 7000 lb axles with electric brakes. All are fine and the bigger ones are a lot more powerful. I recently converted my 6000 lb tandem axle, 12,000 lb gross weight trailer to electric from surge.

If you have tandem axles, go with brakes on both axles.

You can find the parts on-line or at a trailer and wheel supply house.

I highly recommend them!