Instead of getting my gearbox mounted, I got some odds and sods I had kicking around and took a go at redesigning my rear leaf spring bush.
This provisional version doesn't work (two reasons, one obvious which I knew about while making it, one less obvious), but it's close enough to working that I can call this a plan.
If I get this right, it will drop the rear of the spring ~10mm relative to the body. Don't think that's going to upset many things much.
[#]WeirdCarMastodon
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The obvious: yep, I know the leaf spring cannot teleport through the things marked A. I started this with a single piece of random box section that had more or less the right dimensions. It helped me keep everything nice and square as I was building it.
Area B is the more troublesome one. I estimated more space than I actually had for the excess of the bolts to disappear into. I can die-grind myself out some space for the bolt and move the missing reinforcement elsewhere.
[#]WeirdCarMastodon
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Alright, spring bush prototype 2. I've cut out stuff that doesn't need to be there, moved metal elsewhere. That'll actually fit.
I deliberately made the bolts too long on the "it's easier to remove metal" principle. The nut currently sits about where it would be with a leaf spring there. And I only need ~3mm of clearance ahead of the bolts. The poly bush is 3mm thick, and it can't compress to 0mm; that'll leave headroom. Tight, but that's another spelling of "fits".
BUT..
[#]WeirdCarMastodon
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Struck me that at this point, I might as well cut out all of the indicated areas. Or, as will more likely happen, just completely remake this now that I've "tested" the concept.
That would give me enough space to a) make the bolts that go into the chassis captive b) shift the leaf-mounted bush further upwards into the mount, solving the problem of this causing an (inconsequential?) ~10mm downward shift of the rear of the leaf spring. And give me more spare threads!
[#]WeirdCarMastodon
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What I could have done, is designed this all on paper (or even a COMPUTER) ; I could probably have found my final solution weeks ago if I did. Eh, I spend enough time at a desk; chopping up things with an angle grinder then sticking them together with a MIG welder makes me deeply happy.
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Things are escalating.
I'm new to this; my previous ideas for rear leaf spring mounts didn't factor for leaf springs needing to grow along their length as they compress. Oh!
You'd usually use shackles for this, but I don't have room for them (without lifting the rear of my car an unacceptable amount). So prototype 5000 of my mounts is a slider box with UHMW polyethylene bearings. I've seen the 4x4 people use these to good effect; it might work for me.
[#]WeirdCarMastodon
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This should give me about 100mm of slide. I think it's enough. I got that number by measuring the straight distance from mount to mount on the leaf spring, and subtracting that from the length along its curve. That was actually less than 100mm, but 100 is an easy number to remember.
If anyone thinks that is the wrong measurement, please tell me before I weld this together!
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Also, UHMW polyethylene is really fun to work with. I needed to shape it a little after cutting, because the corner inside angle iron is slightly curved. Being self-lubricating (the reason I am using it), a file just bounces off the damn stuff.
But it turns out I can shape - and cut - UHMW with an angle grinder. I had assumed the stuff would melt if I took a grinder to it but nope. There would be one less dead hacksaw blade in the world if I knew this :D
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That's tacked together now. Not sure I want to commit to this & reinforce it any more (and add some gussets for @chris); it might yet need fundamental modifications.
So next up, I think, is to design the shaft for it, so that I can make that, so that can test-fit it to validate the design. So, that is enough car for the day. :)
[#]WeirdCarMastodon
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The plan is for two of these to come off the lathe this weekend. Not sure if I should do four (two for each mount) before I've validated that this design works at all. All I know is that everything looks reassuringly serious with dimension lines and shit.
[#]WeirdCarMastodon #LibreCad
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I had the thought "wouldn't it be neat to machine this assembly out of 304 stainless". This was a fucking terrible idea.
Many tools have died to bring you this information.
[#]WeirdCarMastodon
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Alright, I ended up re-making the shaft assembly out of mild steel. I'm not very hot on the lathe and I'm going to re-make it and the UHMW bearings with much tighter tolerances.
But...more important than that was to validate that any of this even slightly works, so I threw it together with some shims to get things aligned-ish.
It works! The leaf goes almost flat long before I run out of travel in the slider box. Confident it'll be actual flat with some weight in the back.
[#]WeirdCarMastodon
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A minor concern is that when I jack it by the spring as seen here, I end up lifting the car before I get the spring to a point where it would hit the bump stop. I don't think it is binding in its travel; I think this is entirely accounted for by the fact my redesigned mount drops the rear mounting point of the spring a little.
If my mental model of this is correct, that means I might need the mother of all shims between the axle and the leaf spring. Doable!
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@lewis I don't think I've ever had a car that would hit the bump stop with the springs in under "manual" compression. Usually needs road force and the many G forces of a good pothole :)
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@janusfox Good information and thoughts. Maybe I'll hold off on the shims for now. Just not a fan of the nose-down look!
Your reply got me thinking and that's why I like this place (you). It just occurred to me that if I'm in the middle of the slider box's movement when the spring is basically flat, then much more further movement would be reducing the length of the spring thus moving the rear point of the spring forward again. Even more confident that I've got enough slide in that box now.
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@lewis Re: that nose-down look, it dawns on me that I have no idea how ride height is set on a leaf spring! :)
I guess shims under the u-bolts. Trucks are weird I guess with springs designed to handle heavy bed loads, otherwise all the weight in the front and you get "stanced". I guess why they often have the load leveling airbag systems.
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@lewis
À propos of nothing, I once had a 73 Dodge Duster where the rear leaf springs had gone through the trunk floor so that if you opened the trunk lid the car fell to the ground. Not a setup I recommend. Yours looks much better. 👍
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@DenOfEarth @lewis hahahahaha I remember my late uncle always having to fix parts of his Duster where the sheet metal kept turning into bubbly rust
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