Replacing Suspension Assembly On Tandem Axle Boat Trailer

Updated 03/03/2026 | Published 02/27/2026

Products Featured in This Question

Tandem-Axle Trailer Hangers for 1-3/4" Wide Double-Eye Springs - 3-1/4" Tall Front

(126)

$62.21

CE Smith U-Bolt Kit for Mounting 2" Square Trailer Axles - 4-1/2" Long U-Bolts - Zinc

(1019)

$39.29

etrailer Rust-Resistant 4-Leaf Double Eye Spring for 3.5K Trailer Axles - 25-1/4" - Dacromet

(456)

$65.49

Question:

Hello. I’m replacing the whole suspension assembly on my tandem axel boat trailer, including the hangers as they’re nearly rusted away. I have square axels, and not round. For some reason can’t find square axel U bolts. I have the kit APT5 in my cart. The hanger height should be right. Am I measuring from center to center on my current leaf springs to get the correct length? Thanks.

asked by: Jim M

Expert Reply:

Hey Jim, welcome back! You are on the right track with the # APT5 kit. As long as the hanger height, shackle and equalizer length are the same, you can be sure it will work. The equalizer in the kit is 7-3/4" long center hole to center hole. The shackles are 2-5/8" long. Its best to have all this stuff match the stock sizing, just be sure everything will line up correctly.

Also, yes leaf springs are measured center hole to center hole. The best practice is to jack up one side of the trailer so you can measure when not under a load. Feel free to send me that measurement and I can see if we have a suitable replacement. A 25-1/4" long spring like part # e68SR is pretty common for a 3,500 lb axle.

For the U-bolts, we do have kits for square tube axles. The CE Smith U-Bolt Kit # CE23103 is for a 2" square axle and is definitely what I recommend for a boat trailer since they are marine grade. If you need a different size let me know.

Any other parts you are looking to replace? Let me know if there is anything else you need!

expert reply by: Jesse M

etrailer Rust-Resistant 4-Leaf Double Eye Spring for 3.5K Trailer Axles - 25-1/4" - Dacromet
(click to enlarge)

Jim M.

3/2/2026

Hello! I was able to get my best measurements. This is what I got. Leaf springs 20 1/2”(mind you, loaded as it’s late and I didn’t have access to my jack. Equalizer 7 3/4” Hanger 1 1/2” Axel center to center 29” Front hanger to center 25” Center hanger to rear is 25” Shackle 2 1/2” I entered the numbers in good ole ChatGPT and it says my suspension is likely not correct to begin with. The shackles are currently 100% vertical. Part recommendations? Thanks!

Jesse M.

3/3/2026

@JimM Vertical shackles typically mean either the leaf spring or equalizer is too long. It could be the current springs are worn and flexed which can cause this. Or if the equalizer was replaced with something longer than stock, but a 7-3/4" equalizer is a very common standard size. I'd say stick with that equalizer size, then use a longer spring and adjust the hanger placement as needed. So, for the leaf spring use the 4-Leaf Double-Eye Spring # EM88UJ for a 3,500 lb axle. The # APT5 hanger and shackle kit will work great. Then the # CE23103 U-bolt kit (for 2" square axle). For that setup you will probably want to shoot for like a 29"-30" hanger spacing but it's always best to mock everything up and see how it lines up before you dial in the exact placement.