AKA: How to De-Arc Leaf Springs
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4WD leaf pack on top, 2WD leaf pack (with 3″, 5° tapered block) on bottom.
I was, previously, using BellTech 3″ lowering blocks.
I wanted to get away from using blocks for a couple reasons:
- Excessive carrier bearing wear
- Excessive driveshaft plunge depth
- Axle-wrap
- Excessive lateral axle movement
- Excessive pinion angle change
- I wanted less “stuff” hanging low under the truck
To deal with this, and arguably the best way to lower a leaf-sprung vehicle, is to use de-arced leaf springs. BellTech sells a set (Stillen might be the cheapest, and no, I am not affiliated), but I’m too cheap – instead, I’m going to spend five times as much in my own labour.
Interestingly, the BellTech lowering blocks use an aluminum centering pin on the top to locate the axle.
In a Canadian winter (or two, or three…) the road salt causes galvanic corrosion, which eats away that pin. Nice. The “unworn” part was pressed into the block.
Back to the story, here is the saga:
A while back I looked into running 4WD leafs. They have less arc, thicker leaves, and it looked like it could work.
I tried it (top image).
They DON’T work – the center pin is about 1-3/8″ further forward on the 4WD leafs, and your driveshaft doesn’t have that kind of range.
Then I got to thinking. Maybe I could de-arc the 2wd leaf, add the thicker 4wd second leaf, use the 4wd overloads which are arced the correct way….
Based on the packs I measured:
2WD main leaf: 0.282″
4WD main leaf: 0.282″
2WD second leaf: 0.282″
4WD second leaf: 0.319″ (by my calculations, 50% stiffer than the 2WD leaf)
4WD overloads are longer and thicker, but I did not measure them or calculate their spring rate.
So, to get started, I pulled the leaves out.
And disassembled both 2wd and 4wd sets of leafs.
2WD overloads (top) vs 4WD overloads (bottom). This is a Canadian model, so your leaf pack might be different.
I de-arced the 2wd main leaf by first marking 1″ increments along the entire length, and then drawing the existing arc on the table as a reference:
I measured the existing height, and made a mark 3″ lower:
This is my crazy device for re-arcing leaves. The threaded bolt is a stop to ensure a consistent bend at each 1″ point:
Bending. This takes some trial and error, but the system works once you get it going.
(Old picture from when I de-arced the 4WD leafs)
I reassembled the leaf pack with 2wd main, 4wd everything else.
Here it is installed with a 6° shim. The rear shackle doesn’t look happy, and may need to be relocated:
Ride?
It’s different. Less axle wrap. It’s stiffer for sure, maybe 25% by my butt-dyno. It bottoms ~really~ firm – you can tell the springs get stiffer (they are practically hitting the overload). I need to add an inch or so more arc to correct this. I may re-locate the shackle mount too.
The driveshaft ended up placed where it’s supposed to be (the blocks and the angle previously stuffed the driveshaft way into the transmission), so my “shortened” driveshaft was now too short (good thing I still had the original).
UPDATE
So, this is bad, ok:
That shackle isn’t really doing anything – the spring cannot do its job at all. So, either I need to (A) add some more arc, (which would require going back to blocks), or I need to (B) relocate the leaf spring shackle.
I took a weekend to think about it, and decided (B) made the best sense.
So, out came Mr. Plasma Cutter.
And off came the brackets, trimmed back of course, to be welded back onto the frame brackets.
That’s not my poo weld, really it isn’t.
Done, and move on with my life.
UPDATE
I noticed that there was a metallic “clank” at every bump. Turned out the overload leafs were about 1/16″ away from the main leafs, and would slap each other. Not good.
So, I arbitrarily figured maybe an inch of clearance should be good. The larger overload had 1-1/2″ of free arc to it. I took it out and re-arced it to 2-1/4″, and re-arced the second overload (not applicable to US models)to fit.
Increased overload arc top, factory overload arc bottom.
This turned out to be even worse. I was surprised to find out just how much the overloads contribute to every day driving. Arced like this, the truck was a wallowing, floating pig. It was awful.
I lasted two days and pulled the leafs out again.
I cut the ends of the currently unused 2wd 2nd leaf and arced it to match the leaf pack, un-arced the overloads back to 1-1/2″ free arc, and fab’d a simple 1/2″ spacer to (hopefully) account for the added leaf.
Newly molested in foreground.
The leaf pack now sits pretty straight on the truck (which is good), but the overloads are not being utilized (which is bad). So…… I am going to try the flipping the 2wd overloads and installing them instead, as they have even less arc, and are thinner (which might behave a bit better). We’ll see….
UPDATE
The truck was still VERY floaty with the overloads at original arc, despite the third leaf.
I decided not to try the 2WD overloads, but instead I straightened the overloads to have 1/4″ clearance front and back. This required bending the front 7/8″ flatter, and the back end 5/16″ flatter.
I also machined another 1/2″ block (now a total of 1″ rise), as well as a new center pin – the head is 14mm diameter, the shank is 10mm diameter and 90mm long, the threads are 10×1.50mm (because that was the die I had, factory is 10×1.25mm). The pin head is 15mm long to center the 6° pinion shim (rather than a shank spacer I made for the shorter bolts).
All this assembled, and I’m freaking leaving it like this because this has been awful. Total waste of time. I would NOT do this again. I guess the upside is that now I have much smaller “blocks,” plus (hopefully) increased carrying capacity.
Compare to the previous arrangement:
UPDATE
Ok, so I can’t leave things alone.
The springs were still too dynamically floaty. I took the 4WD main overload out and swapped in the 2WD main overload, but flipped it. I kept the 4WD second overload. This was better, but still too floaty.
So then I pulled the 2WD main overload, flipped it back to normal, but de-arced it completely flat on top, and re-installed it. Much nicer. Not low enough though.
I removed the two 1/2″ “leaf” spacers and installed a shorter center-bolt, and machined my old 3″ blocks down to 2″ with a 6° taper and pressed in a new pin (to replace the corroded one). This is where it sits right now. I still feel it’s too dynamically floaty, but I have to leave it like this.
- 2WD main leaf, de-arced 3″
- 4WD second leaf, de-arced to match
- 2WD second leaf, bobbed and de-arced to match
- 2WD main overload, flattened (Canadian trucks have two overloads)
- 4WD second overload, flipped
- 3″ blocks, machined to 2″ with 6° taper
- Relocated shackle mount
- Nissan Quest shocks
Perhaps less shackle angle? That would mean relocating the shackle mount again….. *sigh*
