Changing Shackle Strap Length to Maximize Weight Capacity on Sagging Trailer

Published 11/12/2014

Question:

Re: Shackle Strap length I have a dual axle trailer with 7000# axles. My current shackle straps are about 3inch eye-to-eye. This is a roll-off dumpster trailer, and I want to maximize the weight that it can hold within our GVWR, as previously I have had a problem with the fenders rubbing on the tires even though the weight was under the max GVWR. The double-eye leaf springs ride under the axles, and the shackles connect above the equalizer. So, which will better accomplish the goal, a shackle strap longer than 3inch or shorter? Thanks

asked by: Steve C

Expert Reply:

The first thing I would check on your trailer is the capacity of the springs. You need to be sure the spring capacity is rated at 1/2 the axle capacity. That way 2 springs equal the capacity of the trailer axle for proper fit. Check the arch of the springs with a level top of spring to top of spring to tie bolt.

Next, check your tire size. At some time the tire size and wheel size may have been changed from the stock size. If the stock size is known you can return to that size and it would fix your clearance problems.

Then check the suspension components on the trailer and make sure there is no damage. The Spring hangers, equalizers or shackle straps could be bent, the axle could be positioned incorrectly on the spring seats and/or u-bolt plate or the shackle straps could be stretched. If the shackle straps could be stretched or were replaced make sure the center to center measurement of the shackle straps is the same as those on the other axles and that the holes in the shackle straps are not elongated from stretching or wear. Changing shackle strap size is not going to have much effect on maximizing your trailer weight capacity. Since you have a dual-axle system we usually recommend using 2-5/8" long shackle straps.

The axle itself or spindles, since they were suddenly subjected to all of the trailer weight, could be bent causing the loss of clearance. if your tires seem to be pointing in at the top this would indicate a bent axle or spindles.

If you have a round axle there should be an upwards bow in the tube, if it is straight or bowed down the axle has been bent. If you have a square axle beam, the beam should be straight not bent. Make sure one the spring eye for the front spring isn't below the equalizer and the other spring eye above because the suspension would then be working against itself.

I attached a drawing that shows how a double axle, double eye, trailer suspension is normally setup. If your suspension is configured differently this could be causing the issue.

I have included our FAQ article on double eye trailer suspension at right for you to check out as well.

expert reply by: Chris O