Boat Trailer Springs

  Boat Trailer Springs Boat Trailer Springs

Know what to do if your boat trailer springs ever break. Just like being dead in the water if you don't maintain your motor, you can be "dead on land" if your trailer springs break. This happened to me and is one of the of the things I learned to do that prompted me to record and share these topics with others. As it turned out, several years ago, I wanted to prepare my boat for spring fishing. I went to the storage unit, and noticed that the boat trailer did not seem to be sitting even. I assumed I had a flat tire but upon inspection found my right rear trailer leaf spring broken in two pieces. The picture above is of the suspension showing a four leaf spring that I replaced the originals with. This was six years ago.

  Double Axle Trailer Suspension Diagram of Double Axle Trailer Suspension

  • 1 = Front and Rear Hangers
  • 2 = Middle Hanger - Holding the Equalizer / Stabilizer
  • 3 = Sidebars, Shackles
  • 4 = Stabilizer, Equalizer
  • 5 = Bolt and Lock Nut Location
Needless to say, my plans for that day changed immediately. I thought I was going fishing, instead, I put the trailer up on jack stands, removed the tires on the right side and began to assess what had happened. It turned out that the right rear spring had broken in two, right where the main leaf with the double eyes met the next smaller leaf. Since I could not move the trailer for service, I went to the internet and found www.stengelbros.com website, where I found everything I needed to replace my boat trailer springs.

Replacing Boat Trailer Leaf Springs

  Jack and Jack Stands Jack and Jack Stands

Since the axle, wheels and tires are basically "Floating" via the boat trailer spring suspension system - jacking up your trailer to work on requires extra thought. Place your jack so that it lifts a solid piece of the trailer frame. Be sure to use jack stands, or other solid material that will keep the trailer from falling while you are working with the suspension. Then begin removing the bolts, lock nuts, shackles, stabilizer bar (if you have a double axle) and the u-bolts and axle plates. Keep track of the order these parts off so that you can put them back in the same order and direction. Check for wear on any of these parts, and replace them if excessive wear is seen.

Boat Trailer Springs

  Trailer 3 Leaf Springs Double Eye Double EYE 3 Leaf Springs

There are two primary types of trailer leaf springs: Double EYE Leaf Springs (You will see an EYE hook on each end) and secondly several varieties of Slipper/EYE leaf springs (You will see an eye on one end, and either a slipper-hook, a slipper-radius or slipper-flat on the other end.) Be sure to match your current springs to be replaced with the replacement springs you will order. Stengel Brothers website is excellent and will walk you through all you need to repair or replace your boat trailer springs. I ordered four springs, that were Double Eye, each were four leaf. I did not need to replace any other parts because there was little to no wear on them. I did have to order new U-Bolts as explained below. Within a week the springs arrived with the U-Bolts. Replacing all four springs was an afternoon job.

  Measuring Leaf Springs Leaf Spring Measurements

In my case I had four springs that each were three leaf. They were rated at 1250 lbs each. Since my boat, motor and trailer fully loaded was right at 5000 pounds I determined that I would replace all my springs with stronger leaf springs, and moved up to springs that were four leaf, and rated 1500 lb each. This also meant that I needed to order longer U-Bolts for my axle mount. Next I measured my old leaf springs. Again Stengel Brothers Trailer Springs walks you through how to do this and offers a phone number if you have questions. They have springs of virtually every size, rated weight capacity, and choices of 3, 4 or more leaves. In order to double check my measurements I traced the outline of one spring on a large piece of cardboard, then used a tape measure to measure the dimensions writing down all the dimensions shown in the picture drawing above.

Trailer Spring Shackles

  Trailer Spring Shackles Shackles / Sidebar

Trailer spring shackles (also called SideBars) are made of heavy gauge steel. They are very rugged but over time may begin to show wear. These are part of the suspension assembly that allows the axle to float, but stay in the relative same position. Upon removing my trailer springs and stabilizer I did not see any appreciable wear so I was able to reuse mine with the new springs. If you need to replace these sidebars then make the measurements seen in the drawing, being careful to pick the diameter of the hole that will match the size of your bolt.

Trailer Spring Hangers and Stabilizer Bar

 Shackler and Stabilizer Bars Trailer Shackles, Stabilizer Bar

Inspect for worn, broken or loose fitting parts. Wear or rust would be the most likely cause of needing to make a change. Hangers are used to "Hang" your boat trailer springs from the frame of your trailer. A double axle trailer will most likely have three hangers on each side of the trailer - a front, middle and rear hanger. These hold the front eye of the front trailer spring, the stablizer bar in the middle, and the rear eye of the rear spring. The other ends of the front and rear spring are connected to the stabilizer bar by the shackles (sidebars) mentioned above. Note how the stabilizer bar in the picture above is bolted to the hanger in the middle that is welded to the frame of the trailer and shows the sidebars or shackles. Note the position of the shackles and be sure to replace them in the same position.

Trailer Axle U-Bolts and Plates

 Trailer Spring U Bolts U Bolts and Plate

The Axle U-Bolts, lock nuts and plates secure the axle to the middle of each trailer leaf spring. So are you getting the picture now? Each trailer spring is connected to the frame of the trailer via hangers, shackles/sidebars, and/or an equalizer if you have a tandem axle trailer, then the axles are connected to each trailer spring.

Trailer Spring U Bolt U Bolts

 Trailer Spring U Bolt Plate U Bolt Plate

Boat Trailer Lock Nuts and Bolts

 Trailer Spring Bolts Trailer Spring Bolts / Lock Nuts

As you might imagine heavy duty nuts and bolts are used to hold all of this together. In most cases you will find 9/16 inch lag bolts that are long enough to pass through the spring eyes, bushings, and leave enough room for the nut to be secured. My bolts were 3 inches long. Only the portion of the bolt that sticks through for the nut is actually threaded so that that portion that allows the, springs, stabilizer bar, and suspension to flex around the bushings does not wear because the bolt is actually smooth where it passes through the bushing. (That is what the Lag Means) Lock nuts are used to ensure that the nuts do not come loose. Even so, it is a good idea to check them for tightness several times a season. Lock nuts have a built in plastic/nylon material on about half the threads so that when you tighten the nut that nylon material begins to grab the bolt. You will know it is time to use your wrench when you can no longer tighten the nut with your fingers.

Now you know what I know, and should be ready to tackle your own repair or replacement of your boat trailer springs.

Other Boat Trailer Parts