Shackles inverting

MillWeld · Jul 29, 2011

I've read many threads on the subject but can't find how you determine what shackle length you need. I have just finished replacing all the MH running gear on my tandem with commercial stuff from e-trailer. The old shackles and equalizers were worn but in spite of that I found replacements that were within 1/8 inch (as best as i could measure). One hanger had an elongated hole so I replace it; the remaining ones were not worn. I left a little space around the spring eye so the hanger would not pinch the spring. I installed the new running gear and tires/wheels and found that the shackles invert very easily. The rear tires almost come off the ground and do on only slightly uneven terrain. Seems to me if the shackles were longer this could be prevented but I used the same length as the old - 2.25". So, say you are building a trailer - how do you decide on a shackle length? or do I have a different problem?
Bob

High Compression · Jul 29, 2011

Nothing else has changed? Springs same length? Distance from front spring mount to shackle frame mount? There are a whole lot of variables. Try putting the spring directly under the frame unhooked from the shackle. Add the weight of the trailer, plus the additional weight that it might carry. Measure the distance center line of shackle frame mount hole to center line of the leaf spring hole and that should be the max length that you need your shackle holes to be.

Diamondpilot · Jul 29, 2011

I think it has to do with springs. Did you change them. More than likely you changed the spring rate. You will have to do a new setup to the springs specs which means new mounts.

Chris

TonyF · Jul 29, 2011

MillWeld said:
I've read many threads on the subject but can't find how you determine what shackle length you need. I have just finished replacing all the MH running gear on my tandem with commercial stuff from e-trailer. The old shackles and equalizers were worn but in spite of that I found replacements that were within 1/8 inch (as best as i could measure). One hanger had an elongated hole so I replace it; the remaining ones were not worn. I left a little space around the spring eye so the hanger would not pinch the spring. I installed the new running gear and tires/wheels and found that the shackles invert very easily. The rear tires almost come off the ground and do on only slightly uneven terrain. Seems to me if the shackles were longer this could be prevented but I used the same length as the old - 2.25". So, say you are building a trailer - how do you decide on a shackle length? or do I have a different problem?
Bob

Go here, bottom of page and check the installation of your setup. Double-Eye Trailer Suspension System Review | etrailer.com

Generally, tandem springs go above the shackle, while singles go below. You can easily see the difference using the link above.

MillWeld · Jul 29, 2011

DP, What is spring rate?

Yes, I did change the springs to 25.25" eye-to-eye, 4800# (item PR4). My hanger distances are: 29.5 and 29.5 on the left side and 29 11/16 and 29 5/8 on the right. e-trailer specifies hanger distances of 29.5" for these springs so the left side is spot on. The right side is off a bit - maybe wear? Is being off 1/8" and 3/16" enough to require replacing the hangers? Both rear axle shackle sets show the inversion, not just the right side.

MillWeld · Jul 29, 2011

Thanks, TonyF. That link led me to a FAQ sheet on trailer suspension in which e-trailer recommends a certain kit (Dexter APT5) for tandem trailers that contains hangers, shackles and equalizers VERY different from the MH parts I am replacing. (The shackles and equalizers are longer). I never saw the description of this kit so I ordered individual parts the same size I am replacing. DUH - what's wrong with that?

I am still awaiting a reply from e-trailer and maybe that will shed some light on the dilemma.
Bob

Diamondpilot · Jul 31, 2011

Spring rate is simply another way of saying load capacity.

Chris

MillWeld · Aug 5, 2011

Well, I did buy that kit consisting of longer shackles and equalizers and it did the trick. :thumbsup:
Photos show a reasonable (I think) angle for the shackles with my 3000 lb tractor on the trailer. I think the conversion of MH axles/wheels to commercial is finally over and successfully at that.
Bob