Optimum Shackle Angle?

['05TJLWBRUBY]

What is the optimum shackle angle for standard springs on a 3500# axle setup?

My axle builder said to make it 10 degrees backward so that when it flexes, it will kick back like it should naturally. Makes perfect sense and follows suit with all my other trailers and standard shackle logic. However, then he said just measure forward 1" of my spring eye measurements for the back mount and that will be about right. Well, I measured 1" forward, then laid everything out and fit it together and it looked way too steep. Sure enough, it was 27 degrees. 1" forward and 27 degrees is a far cry from the 10 degrees he said to make it so I'm curious what it really should be. 10 degrees almost doesn't look like quite enough, but I could be wrong. My other trailer that I have here at the house is at 5/7 and 0/-2, but it's in rough shape and pretty beat up. Consequently why I'm building the new trailer a little more stout to handle the abuse a little better. I'd like to get a good idea of proper shackle angle to make this one right if possible.

Thanks in advance,

Best of Luck,

Mike

 

[CJ2AinAZ]

Shackle Angle

Mike, Couple of variables to consider...
Shape of the springs, if you have a significant curve to the spring, then you do not have to worry about the shackle flipping to the "inside" as much as if the spring is flatter. Think curved spring, less angle ok.

I run 45 degrees on my Jeep. However the 45degrees allows for a lot of droop as the spring moves. This effectively gets you more travel. Of coarse the shackle length plays in here too. More droop, will keep the rubber side down, just depends on how much of an offroad trailer you are building. I found by getting a flexible piece of wood the same length as the spring. I could play with the shackle length/angles to dial in what I really wanted. Just make sure the shackle won't ever hit the frame at full compression.

My guess is the axle builder is giving you the on road answer. If this is for offroad, I think the longer shackles are worth considering.

Good luck!
Scott

 

['05TJLWBRUBY]

Thanks for the info. Yes, these are pretty short shackles-standard trailer spring variety. I didn't measure them, but I'd guess 3-4" in length overall roughly. Springs are something like 26.5" eye-eye 3 leaf pack. I ordered the longest I could get that was a standard size pack and had them remove a leaf as most trailer leaf packs are too stiff anyway. Thought I'd try this and see how it does, then go from there. Yes, they are arched a fair amount.

Only info I could turn up was anywhere from 0-10 was acceptable, so I went with 6.5. Actually set it at 6, but tacking it in pulled it a bit, which is fine. They're both even. It'll settle a bit more under load of itself when it's flipped over, then more yet when it's actually loaded so it should be OK I'd think. They're just tacked in for now so I can play with them if it doesn't work out right. I'll update the build thread here in a second.

Thanks for the info!

Best of Luck,

Mike

 

[Markgyver]

I have always moved them in 1" from plumb and that has worked for me.