Spring problems are more likely to be caused by incorrect rear hanger location than wrong size spring.
90% of Shackle Springs have hangers located so that the axle is the centre of the mudguards but the rear hanger can be out of the correct location by as much as 35mm.
35mm is a disaster and leads to broken spring at the eye, Hangers installed the same length as the spring means any shock loading causes the spring eye to smash into the rear dumbjack. I have no idea why or who coined the name “dumbjack” but my guess is, it was not a complimentary term.
The image on the right is perfectly installed for a spring at NO LOAD. Notice the shackle plates are pointing at 7 pm no load? When the load come on the position changes to 5 pm at full load.
Can you imagine full load at 3 pm? Clearly, 3 pm is the wrong position.
Rocker Roller Spring Hanger Locations
Hanger locations selected incorrectly can have disastrous consequences.
The towing equipment in the right-hand image is the result of tandem spring hangers in the wrong location on a 4.5t bob cat trailer.
The spring problems here were an incorrect centre of balance was selected to hang the centre hanger. We also found the front and back hangers welded in the wrong location.
Although it can be tempting to install these rocker rollers yourself, it is better to get an expert to do the installation. After all, the experts must provide warranty on their work.
So how do I get my hangers right?
First of all, go out and measure your hanger measurement and then measure your spring width eye to eye.
If your hangers are the same length as you spring measurement then there is only ONE FIX.
For 710mm and shorter springs, your hangers must be 25mm longer than your springs. So move your rear dumbjack.
To move this dumbjack, you will need to grind it off and but 2 more dumbjacks. Tack weld them first, double check measurement then weld both dumbjacks into place.
Your rig will now tow much better as your suspension will perform perfectly. The opportunity for vibration fatigue has been defeated.
The image on the right is an Outback Offroad spring. Springs longer than 710mm should have hangers welded 35mm longer than the spring eye to eye measurement.
Now your hanger and spring problems are fixed, you have now finished with your welder.
Shock absorbers are an excellent option to add to your rig to give it an even smoother ride. Review the shock absorber article here.