Determining Correct Replacement Suspension Components for Tandem Axle Boat Trailer

Updated 09/03/2013 | Published 08/29/2013

Question:

I have a production built boat trailer,manufacturer unknown. It is a tandem axle. The current spring length is 25.25, center to center on the hangers is 27inch I think, equalizers are 6.125. As you can see in the picture the shackles rub against the center hanger. Also, I have blown the tires on each side of the rear axle. Is this an issue of someone installing springs that are too long? Should I replace these with 23.25inch springs such as the the # 1724? It seems the rear axle is carrying too much of the load.

asked by: Charles S

Helpful Expert Reply:

Thank you for submitting the photo of your boat trailer showing the center spring hanger, shackle straps and equalizer.

Based on the photo it does appear that non-standard replacement parts may have been used to repair or modify the suspension at some point and this could certainly have contributed to the rear axle tire failure. If the equalizer cannot function correctly (due to the use of fabricated or non-standard replacement shackle straps) then too much of the total trailer load may be applied to the rear axle and this could have lead to the rear tire blow outs.

The best way to proceed is to take measurements of your existing suspension system to allow you to select appropriate replacement parts. The measurements needed are: 1) the distance from the front hanger hole to the center hanger hole; 2) distance from the center hanger hole to that on the rear hanger; 3) the distance between the centers of the two axle u-bolts; 4) the vertical distance between the axle center and the trailer frame; and 5) hanger height. I have attached a diagram showing where to take each of these measurements. Note that it is more accurate to measure the hanger spacing than to rely on the existing spring length; spring length may vary slightly depending on condition and wear.

If your measurements show, for example, a hanger spacing of 29-1/2 inches, a u-bolt spacing of 33-1/2 inches, an axle diameter of 3-inches and a hanger height of 3-1/4 inches (a fairly common configuration) then you could use kit # APT5. This kit includes hangers, equalizers, shackle straps and bolts and works with trailers with tandem, 2,000-lb to 7,000-lb axles. I have included a link to this part for your reference.

I have also included a link to a helpful article concerning double-eye trailer suspensions that might be useful to you along with a link to our main page for hanger kits for double-eye suspensions.

expert reply by: Adam R