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Replacing noisy Harbor Freight Slipper Springs


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jscherb

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#11
(08-31-2013, 09:14 AM) drswyo Wrote: I just put a new axle on my modified HF trailer using the set up suggested by jscherb. There is a potential problem with the spring and shackle using the stock holes for mounting.

The shackle straps sit just forward of vertical, so as the spring compresses and elongates the shackle has to swing down through it's arc toward the ground, past the vertical position, then up and back through the rest of the arc. Hope I'm explaining that clearly, I'm not clever enough to try and illustrate that.

The result is a very steep climb in spring rate right at the beginning of the suspension travel. Coming from a background in rock crawlers, this makes for a very non-compliant ride.

Seems like the easiest fix is to drill a new rear mounting hole a couple inches forward of the stock hole so that the shackles are always pointing to the rear, but not so far that the spring eye can hit the frame under compression.

For now I'm going to wait until I get my box built and loaded to see where the shackles sit with the spring compressed after dialing in the spring rate by removing leafs, then I'll think about re-positioning the upper shackle bolt.


Yes, the straps angle forward from vertical, but because the spring is angled downward by the straps, the effective angle between the spring and the shackle straps is 88.5 degrees, meaning that relative to the spring, the shackle strap angles rearward towards the bottom by 1.5 degrees. Here's the math.

- The distance between the spring holes in the Harbor Freight spring bracket is 20.5" center-to-center.
- The Tractor Supply springs have holes that are 20.25" on-center.
- The Tractor Supply #1075286 shackle straps are 2.5" on-center.

Since the holes in the spring bracket are spaced 0.25" wider than the holes in the spring, that causes the shackle straps to slant forward from vertical at the bottom. 0.25" over 2.5" results in an angle forward of roughly 5.5 degrees.

Because the rear of the spring is held away from the spring bracket with the shackle straps and the front of the spring is bolted directly into the spring bracket, the spring slopes down towards the rear at roughly 7 degrees (2.5" slope over 20.5").

The angled orientation of both the spring and the strap results the 88.5 degree angle between the spring and the straps, meaning the effective angle of the shackle strap relative to the spring is 1.5 degrees towards the rear at the bottom under no-load conditions, which is within acceptable range for the spring-to-shackle angle. So even though the shackle strap is visibly angled forward relative to true vertical, relative to the spring it is angled back 1.5 degrees. And because of this, during compression, while apparently the shackle strap would seem to swing downward through its arc towards the ground, relative to the spring it is only swinging upward through its arc, so there's no problem.

Or, if you're not comfortable with the 1.5 degree effective shackle angle under no-load and would rather have your shackles angled backward relative to true vertical, then as you said you can simply drill new holes in the HF spring hanger bracket to change the angle of the shackle straps:

[Image: HFShackleSprings2_zpsd567e443.jpg]

Scott

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#12
Thanks Jeff, yes in relationship to true vertical, the shackle is over the top of the arch and pointing slightly rearward.
Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping

drswyo

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#13
I appreciate all the time that Scott and jscherb put into their replies.

Thanks for the math, that makes sense. Looking at it again I can just tell that the shackle is just below 90 degrees relative to the spring. 1.5 degrees is hard to eyeball, wouldn't have believed it without the math.

Happy about that, didn't want to take the time to drop the axle and drill a new hole anyway.

Here is a pic, you can see why it looks like the shackle is pointed the wrong direction, but if you look closely at the angle of the spring it makes sense.

When I get outside to do some work I'll see if I can line up some straightedges with the spring and shackle and take a pic to illustrate jscherb's explanation.

[Image: IMG_0790.JPG]

drswyo

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#14
Here is a shot showing that the shackle is actually pointed backwards relative to the spring. Yardstick is flat on the spring perch, but it was hard to get into the photo to show it and the angle.

Math works!


[Image: IMG_0797.JPG]

armyRN

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#15
Don't be afraid to drill a few holes in the trailer's frame. Here's my modified suspension with longer springs with a shackle at one end (also see post #3 on this thread). They are 26" long springs, and the pivot points on the frame are 25.5" apart so the shackle has a slight angle back to them. Combined the springs are rated for 1150 lbs.

http://www.jeepforum.com/forum/f27/mini-...st14711779

[Image: Trailersuspensionmountedup1_zpsd16cce90.jpg]

Scott

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#16
Here is a spring retrofit I’m prototyping for the HF frames. It will use a double eye spring that is about 9” longer, has a flatter profile and actually compresses for a notably improved ride. They are 4-leaf packs which are good for a 1150 lb GVW and tunable for lower loads by removing leafs.

Here is a comparison
[Image: 35675257555_23d30894c8_b.jpg]
Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping

galerdude

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#17
That looks pretty sweet, Scott! What's your estimated time 'fore you release a price and availability?
Thanks All & Cheers!
Gale
Link to my modified Explorer Box Build Journal.

jscherb

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#18
(09-27-2013, 04:48 PM) Scott Wrote: Here is a spring retrofit I’m prototyping for the HF frames. It will use a double eye spring that is about 9” longer, has a flatter profile and actually compresses for a notably improved ride. They are 4-leaf packs which are good for a 1150 lb GVW and tunable for lower loads by removing leafs.

Here is a comparison
[Image: 35675257555_23d30894c8_b.jpg]


The longer and slightly more compliant springs will be an excellent enhancement to the HF frame!

Scott

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#19
Gale, expect kit to be around $125, could also sell individual parts if someone wanted to weld there own hanger brackets. Just need to check a few things before offering them, could make you some in a week or two.

Jeff, actually much more compliant. When pulling a leaf out, I debur the leaf ends and spray between the leafs with a dry teflon lube which also helps.
Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping

galerdude

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#20
(09-28-2013, 05:23 AM) Scott Wrote: Gale, expect kit to be around $125, could also sell individual parts if someone wanted to weld there own hanger brackets. Just need to check a few things before offering them, could make you some in a week or two.

That sounds great! Please post when details are worked out. Would be interested in complete kit. Would I be correct in assuming it could be either bolt on or weld on? I'll bug you later about shipping cost.
Thanks All & Cheers!
Gale
Link to my modified Explorer Box Build Journal.
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