Trailer Suspension Mounting – Misdirection !!

Shopping online is both a boon and a bust.  It’s great access to a wide variety of components, but it’s a bummer when misleading info causes extra work and frustration.  That brings us to this Customer Story of misguided information about trailer suspension mounting.

As we start a new project, often we don’t know what we don’t know.  We don’t know what questions to ask, or what info to search — because it is new.  We’ve been there too.   At Mechanical Elements we have great info to help, but if you don’t know what you need, it’s kind of hard to find.  So, this is a Story of Learning.

I wish to emphasize this is a story of learning.  The subject of trailer suspension and mounting is a good illustration to help us all learn.  I am impressed with this customer because he caught the issue and was willing to seek help.  It’s a good example of how in DIY we often learn as we go.  So, when things are not as they seem, it may be time for learning.

The Back Story

A customer contacted us with an axle issue.  He said “I have some suspension clearance issues on a trailer . . .” and want to switch from Underslung Springs to Overslung Springs as a solution.  “Will it work?”  After some email and photos,  I could see that the axles do hit the frame because there is very little clearance.

Trailer Suspension Mounting in TandemThe customer recently repurposed his trailer including a new suspension.  He did it right by properly removing the old spring hanger brackets, then buying new components for it.  Unfortunately, after mounting everything, he found the axles did not have enough clearance.  At the point of contacting us, he was a little frustrated.

Certainly, flipping position of the leaf springs (under to over) is one way to add space.  Yes, it will change clearance to the axle beam, but, there is bigger problem.  See the image.  With this axle setup, there is not room for the equalizer motion.  See the yellow arrows.  That is also important.

How Did The Trailer Suspension Mounting Get This Way?

In our discussion, the customer said he got the parts from an online retailer.  I normally like that web store, so I followed his links to the product.  He said, “Here are the trailer springs, and the hanger kit that I bought.”

Sure enough, if you read the sales info, check the images, and watch the video, it all sounds good.  But, it won’t work.  This set of parts does not give sufficient space for suspension motion.  Even if we forget the axles for a moment, the shackles will hit the trailer frame when the kit mounts on a beam.  The center hanger is too short for the equalizer with those shackles.  The design is just wrong.  (See animations of equalizer action.)

Maybe the 5-Star reviews are from folks that blindly buy, without looking at function?  I congratulate this customer for seeing it.  I give him kudo’s for seeking to fix it, because trailer suspension mounting is certainly one of the critical things to get right.

The springs are what they are.  I think they provide good spring dimensions on the website.  Since they don’t have trailer suspension mounting hardware, then documenting dimensions is fine.  Some springs have more arch, but these give enough info to calculate if they will work.  In other words, the problem is not the springs.

What do we learn?
  1. We don’t know what we don’t know.  We try, of course, but we must expect to learn new things as we go.
  2. It’s worth the time to look at the measurements and do some calculating to see if things will fit.  That would have saved this customer a lot of frustration.  (I don’t blame him, because he didn’t know what to look for.)
  3. Sales pitch is often misleading.  Read it, but also, do your homework.
  4. Try things out before welding them on solid.  (This tid-bit of advice has saved my bacon many times.)

It’s unfortunate the customer did not dry fit the trailer suspension and mounting before welding.  That too would have saved a lot of headache.  I always recommend dry fit — because I have also learned similar lessons by hard experience.

How Do We Solve This Suspension Mounting Problem?

Now that the brackets are all welded on, how do we correct the trailer suspension mounting clearance issues?  Here are some choices:

A.  Start Over.

The first, most obvious answer is to start over by cutting these brackets off (again), then replace them with taller brackets.   That will solve all the issues (both for the axles and for the shackles).  This is arguably the best choice in most circumstances because it makes things foundationally right.

Also, starting over gives the opportunity to add buffer pieces between the spring hangers and the frame — especially since any grinding nicks in the frame that happen during bracket removal will weaken it.  A buffer piece will cover the area and provide added strength for the new spring hanger brackets.

B.  Go Overslung

Springs Overslung and UnderslungTo achieve more clearance for the axle, it is possible to change the springs from under the axle to above the axle.  From underslung to overslung.  This image illustrates the idea.

While it will definitely change clearance to the axle, it won’t change clearance around the shackles at the equalizer.  So, one way or another, we need to increase the height of at least the center spring hanger.

We have seen this problem before.  Read the article “What is wrong with this Picture?

If we change just the center hanger, we will sacrifice just a little stability — but, maybe not enough to notice.  (It depends on many other factors.)  It is easier than starting over, but not as clean for the end result.

While, simply changing from Underslung to Overslung won’t solve the whole problem, it’s worth mentioning.  He asked about it, so that is our answer.

C.  Pair New Hangers with the Old

Paired Spring HangersBecause of his situation in the build, the customer asked for a way to put the new trailer suspension mounting hangers on the trailer without removing the old.  That’s contrary to the option above, but since it is a reasonable request, together we came up with the following ideas.

The first idea puts new, taller spring hangers directly adjacent to the existing ones.  By welding to the short ones it will stiffen and support the new tall ones.  This will work great for the front and back hangers.  However, with the center brackets, a portion of the old short one must be cut away to allow shackle clearance.  Perhaps best cutting it at an angle.

On the negative side, it shifts the axle position 2.5″, so that’s not so good.  While axle position is really important, moving an inch or two is usually OK.

D.  Stack New Hangers on the Old

Stacked Trailer Suspension Mounting HangersCan we stack new spring hangers on top of the existing short ones?  This image shows the second idea.

Remembering that these are a pair of 2000 lb axles, and the brackets are actually for 3500 lb axles, then yes, this idea seems reasonable.  The double bracket is likely stiffer than a single bracket in the one direction, but maybe not the other (when we take the welding into account.)

Also tall brackets are usually longer so in the end this idea doesn’t look quite as strong.  However, there might be a way to improve this idea and improve the stiffness.

E.  Stack The Hangers +

To improve the idea above, a nice way to stiffen the hanger stack, is adding a bit of angle to tie it all together.  The orientation is in this next image below.  It strengthens the bracket stack both front to back, as well as side to side.

Just like above, we also need to make sure the center bracket has clearance for the shackles.  A simple angle cut makes sure they will not interfere.  Stack short brackets for front and back, then stack the slightly taller brackets for the center.  This gives the needed clearance for axle movement, and for the equalizer motion.

Option for Trailer Suspension Mounting

Final Follow-Up

Hopefully the customer will send photos when he completes the new trailer suspension mounting.  I hope it all works out well for him.

In the meantime, because I like to help people along the way – and because I dislike misleading sales info, I left this comment for the bad product.  I left it as a comment, not as a review.

Thank you for selling this inferior product.  I was able to help a customer, and write a blog post about not trusting everything in a sales pitch — using this product as an example.  Please tell customers that this set of parts does not allow proper suspension motion clearance.  The center spring hanger is too short for the length of the equalizer with that length shackle.  The shackles will hit the trailer frame if it is mounted to a straight frame member.  Also, unless the springs have a very large arch, the axle will hit the frame.  This is a poorly designed product, and I think you should tell your customers about the problems they will have.

Hopefully someone at the store will look at it long enough to see the problem, then remove it from their site.  They have not contacted me back about it, so maybe they don’t care enough.  Oh well.  You now know one more thing to help in your trailer build.

We wish you the best of luck with your trailer suspension mounting projects!


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