Can I Use A Higher Rated Leaf Spring On A Shoreline Boat Trailer?

Updated 06/17/2024 | Published 06/09/2024

Question:

Hi, I have an older tandem axle Shoreline boat trailer which I use for my 24-foot grady white. I recently replaced my leaf springs, including shackles, equalizer, and ubolts. When my boat is off, everything looks finesprings have a normal amount of curve. But when I load my boat on the trailer, the rear leaf springs flatten out and the equalizer pivots forward so the shackles are very close to the trailer frame and may even touch on unlevel ground. The springs are rated for 3500-lb axles and I would estimate the boat to weigh 4000-4500 lbs total including motor, fuel, accessories. I took the trailer to a local shop and they said the springs look to be installed correctly and they should hold my boat fine. But it seems the rear axle and springs may be taking more of the load than the front. I was considering either trying heavier springs maybe 6000-lb rated, part e47SR in the rear, or possibly moving the bow stop forward to move the boat forward, though I only have 6-8 inches of space to move it foward. I was curious if you had any suggestions one way or another. Thanks

asked by: Ben E

Expert Reply:

Hello Ben. Anytime we see a trailers suspension go "wonky" like that it is almost always due to incorrectly sized suspension components. Since you say you replaced things recently, I suspect this is the issue. If the equalizer is pivoting forward and hitting the frame, this could mean your springs are too long. I do recommend that you stick with a spring that is appropriately rated for your trailer. You would not want to put a 6,000 lb spring on a 3,500 lb axle.

expert reply by: Jesse M

Ben

6/17/2024

Thanks Jesse. I had a local reputable trailer parts store measure the eye-to-eye length of the old springs with them on the trailer (although their experience level varies depending on who is working that day). But I also read on a forum that measuring old leaf springs can over-estimate the length if they have flattened over time. The new ones are 25 1/8". I don't have the old springs anymore, but not sure they would be much help. What length would you suggest? I see 24 7/8, 24 5/8, and smaller. Is there a good way to measure without having using the old springs as a reference? Thanks again. --Ben.

Jesse M.

6/17/2024

@Ben Yes it is possible to get a bit of a false measurement on old leaf springs. They can flatten out a bit over time. Also if the springs were measured with the trailer still on the ground they are going to measure longer than they should. Depending on the condition of the spring and the weight of the trailer leaf springs can flex up to 1". It is hard to say exactly what size spring will fix the issue, but of the sizes you listed, a 24-5/8" is what I suggest trying next. Note that the equalizers and shackles also need to be the same size as the original parts. If these are sized differently it could throw off the suspension in the way you described.