How Axle Spring Seats Work

An axle spring seat is a small, but very important piece to make sure your trailer -- and your cargo -- arrive safely.
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You can be forgiven if you've never noticed the axle spring seats in your trailer. They're small, inconspicuous and are usually hidden beneath the axle. The job they do in maintaining your trailer's alignment is not particularly glamorous, but if they suddenly ceased to exist, you'd definitely notice. Your trailer would not only have a much bumpier ride, but it would probably fall apart. That makes axle spring seats pretty important.

An axle spring seat is a small brace that literally sits under the trailer's axle, attaching it to the springs and keeping the axle from falling out. In that role, it serves both to maintain the trailer's alignment and to help absorb shocks. It's a tough piece of metal and very dependable, not needing a lot of maintenance.


The axle spring seat is a small portion of a larger assembly, which also consists of the axle, two or more leaf springs, hangers and, in some cases, an equalizer.

So let's look at how this assembly works. The hangers attach the springs to the trailer. The leaf springs extend from the axle and serve as a shock absorber between the axle and the trailer. If the wheel hits a bump, the spring absorbs it and lessens the effect of the bump on the trailer. For a trailer with two axles, two more leaf springs extend between them, united in the center by an equalizer and attached to the spring seats. This evens out the effects of shocks between the two axles. The axle spring seats serve as anchors for the springs, so they play a central role in this process.

But what if something goes wrong with the axle spring seats? Is this something you should worry about? And if it happens, is there something you can do about in on your own? We'll look into that in the next section.


Installing Axle Spring Seats

A u-bolt (similar to what is shown here) is usually the culprit if something goes wrong with an axle spring seat -- although problems do not arise often.
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Axle spring seats are attached to the axle using a U-bolt. The bolt loops over the top of the axle and is attached to a plate underneath by a pair of nuts. The axle spring seat, which sits under the axle, is held in place by the plate and has holes that allow hooks on the leaf springs to be attached to them. Can you install the seats yourself? Yes, but in most cases it's unnecessary. Axles for trailers are typically sold with the seats already welded in place.

But hat if something goes wrong with the axle spring seats? The results, obviously, would be disastrous. Without the seats serving as an attachment for the springs, the trailer would begin to vibrate wildly every time it hits even a small bump. The trailer would begin to shake apart and the axles would be in danger of falling out.


Should you worry about this? Probably not. Trailer service technicians say that they rarely, if ever, see problems with axle spring seats. When problems occur, usually in older trailers, they tend to involve the U-bolt. The ends of the bolt can wear down, causing the alignment of the axle to slip. There is some risk in this situation that the spring seat will become unattached. It is possible to buy a new U-bolt (and a new axle spring seat, if necessary) and attach it yourself. However, a better -- if more expensive -- option is to buy a completely new axle, complete with preinstalled spring seats. Unless you have absolute confidence in your ability install the new seat and to weld it in place, going with the new axle is safer.

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