Cutting coil springs

[Shran]

Here's the deal - I did my solid axle swap last year and have been running very stiff 3" 73-79 F150 lift coils, 'cuz that's what I had. I picked up a pair of what were supposed to be 3.5" Duff progressive coils that ended up being 5.5" ones instead. I threw them in just to see where I'd be sitting and it is WAAAAAAAAAAAY too high in the front - like 4" or so higher than the old ones.

So I need to drop it back down for obvious reasons. Would I be OK cutting a loop or two off the bottom of the Duff coils, or just putting the old ones in and getting something else? I do want coils that perform well and I also know that cutting the coils increases the spring rate, but I don't know by how much... I don't want to end up with something that is stiff as what I already have.

 

[ThatGuy]

I spoke with the guys at Duff about this very thing. I plan on using the 5.5" EB coils on my next TTB project but wanted to know about cutting from the bottom. I was told that it would not affect spring rate just lower the ride height. Their progressive rate coils are basically 2 linear rate coils joined together. Cutting from the bottom will take some of the higher rate out leaving more of the softer rate behind.
Cut 180 degrees from where the stock end is until you end up with the desired ride height. 2 cuts will be 1 complete winding of the coil. Better to make more cuts than end up too short.

 

[RangerSVT]

And whatever you do DO NOT use a torch/plasma cutter to cut the coils, use a cutoff wheel/hacksaw/sawzall...Using a torch will heat the springs and destroy them
SVT

 

[Shran]

I spoke with the guys at Duff about this very thing. I plan on using the 5.5" EB coils on my next TTB project but wanted to know about cutting from the bottom. I was told that it would not affect spring rate just lower the ride height. Their progressive rate coils are basically 2 linear rate coils joined together. Cutting from the bottom will take some of the higher rate out leaving more of the softer rate behind.
Cut 180 degrees from where the stock end is until you end up with the desired ride height. 2 cuts will be 1 complete winding of the coil. Better to make more cuts than end up too short.

Cool, that is exactly what I needed to know. Thanks!

And whatever you do DO NOT use a torch/plasma cutter to cut the coils, use a cutoff wheel/hacksaw/sawzall...Using a torch will heat the springs and destroy them
SVT

Heh... I know that, thanks for the reminder though. Hacksaw and sawzall don't work very well, the spring steel is stronger than the blades.

I saw a guy at the last mud drag I went to that had welded two coil springs together for lift in his Jeep...

 

[NMB2]

I was told that it would not affect spring rate just lower the ride height. Their progressive rate coils are basically 2 linear rate coils joined together. Cutting from the bottom will take some of the higher rate out leaving more of the softer rate behind.

I cant even believe duff would say that.... wait... yes I can.

that is false, cutting the coils from the bottom will make the bottom rate stiffer.

 

[ThatGuy]

How is that?

 

[4x4junkie]

Fewer turns on the coil.
Fewer active coils = stiffer (higher spring rate). The fact they are variable-rate doesn't change this, you still have fewer windings on the coil.

 

[ThatGuy]

Yeah, I was about to put in that I've been Googling for spring rate calculators. All the ones I've found are for linear coils though. Any links to one for a progressive rate coil? I have the build sheets for the JD 3.5" & 5.5" EB coils and I'd like to input the numbers and come up with for sure answers. I'm not arguing the point but to me it seems like with more of the stiffer part of the spring gone the softer part would cancel that out????

I dunno, I asked, that's the answer I got.

 

[feellnfroggy]

I cant even believe duff would say that.... wait... yes I can.

that is false, cutting the coils from the bottom will make the bottom rate stiffer.The ratio of stiff rate coils to soft rate coils will lean more towards the softer rate when you cut the stiff coils. Less stiff rate coils means more travel in the soft range.

Cuz your a spring master right? The duff coils are ordered to duff specs. the stiffer tighter wound coils are towards the bottom of the springs as they are installed. They have been in business doing this stuff for how many years? 35, they might know what they are talking about with theyre product.


My only concern is safety, but your not cutting a stock spring so it might be alright.

 

[Shran]

My only concern is safety, but your not cutting a stock spring so it might be alright.

Not worried, coils have been cut a million times with no safety issues... as long as you do it right. I also have a solid axle so I am just changing the ride height, not alignment or anything else. Just was curious how much it will change the spring rate - if it's a waste of time to cut them down.

 

[JohnnyU]

I ended up cutting about 1.25 turns off of my progressive rate springs from Tom's Bronco Parts. In my case, the lower rate wraps were collapsed on themselves in turn giving me an infinite spring rate. By removing that material, I effectively increased the spring rate to the point that those wraps were no longer binding and there is gap between all layers. The truck sits lower and flexes MUCH better.


Do it, but cut small amounts like 1/4 turn at a time.

 

[Shran]

I ended up cutting almost one entire turn off the bottom which brought me down at least 2-3". It still sits slightly high in the front but it is good enough. Thanks for all the help.

 

[NMB2]

Cuz your a spring master right? The duff coils are ordered to duff specs. the stiffer tighter wound coils are towards the bottom of the springs as they are installed. They have been in business doing this stuff for how many years? 35, they might know what they are talking about with theyre product.


My only concern is safety, but your not cutting a stock spring so it might be alright.

I will be the first person to tell you, I am not impressed by James duff products, at all.

Progressive rate coils to begin with are a joke, and there is NOTHING special about duff coils. I don't care how long duff has been in business... if you're wrong you're wrong, and what they told him is a lie.

EDIT:

I just noticed you added a little something in red to my quote. That might look good on paper to you, but its also wrong. Have you ever wheeled a truck with these springs? the upper wraps just lay on eachother, which causes a shitty ride, clanking, banging, and especially, no added up-travel from chopping lower wraps out.

 

[bobbywalter]

sorry......

 

[gwaii]

there are 3 key factors that determine spring rate-wire diameter(bigger=stiffer),coil diameter(bigger=softer),and number of coils(more=softer).as has been noted previously,the close spaced coils collapse on each other quickly.when this happens it takes them out of the formula for the rate,thus increasing the effective rate.
since the wire diameter and the coil diameter remain constant,this is the only thing affecting the variable rate.to determine how the rate will change on these springs,simply calculate how much compression will be required to bind the close coils.if theres 5 close coils and 5 wide coils,and the close coils have a 1" space between them,they need to compress 5" to attain coil bind.the pressure reqiured to do this will be across all coils,so the others will compress the same amount-so in this case 10" compression will give coil bind on the close ones,effectively doubling the spring rate at that point.if the rate is 100lbs/in,then at 1000 lbs pressure on the spring,the rate will increase to 200lbs/in for the rest of the travel.

if practical,i would cut from the close spaced end,not the wide spaced.