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Rear Spring Options For Lifting Your WD21 Pathy


88pathoffroad
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  • 3 weeks later...

Hi,

I just came back from the junk yard and I got a set of springs from a 2000 cherokee sport. the measurements are 4in ID, 5 5/8in OD and 22in long, the diameter is about 5/8in and I counted 12 coils. Sinse these seem to be thicker and taller than anything I have seen in this thread Im asuming they are lift springs for the Cherokee. :shrug: Has anybody used this type of springs before? My pathy is my only mode of transprtation so I cant aford to have to disasemble the rear end a bunch of times to re cut this springs. any sugestions will be apresiated.

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Those do sound like some kind of a lift spring.

Double check your measurements, 5 5/8" sounds way too big - should be about 5 1/4.

 

If they are 5 1/4" OD, you probably can cut them down to make them physically fit, but I'm afraid you're going to find them wayyyy too stiff.

If the wire is truly 5/8" in diameter (.625"), they are going to ride like an unloaded one ton truck. And I suspect they really are that big in diameter. Since the spring rate goes down as the total wire length increases, the designer would have had to increase the wire diameter to compensate.

 

Doing some quick math, a wire diameter of .63" will result in a spring more than twice as stiff as what you have now - ouch.

On the plus side, you could haul ALL your fat friends around and the rear of the truck won't be squatting much at all!

Edited by mws
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Those do sound like some kind of a lift spring.

Double check your measurements, 5 5/8" sounds way too big - should be about 5 1/4.

 

If they are 5 1/4" OD, you probably can cut them down to make them physically fit, but I'm afraid you're going to find them wayyyy too stiff.

If the wire is truly 5/8" in diameter (.625"), they are going to ride like an unloaded one ton truck. And I suspect they really are that big in diameter. Since the spring rate goes down as the total wire length increases, the designer would have had to increase the wire diameter to compensate.

 

Doing some quick math, a wire diameter of .63" will result in a spring more than twice as stiff as what you have now - ouch.

On the plus side, you could haul ALL your fat friends around and the rear of the truck won't be squatting much at all!

 

Double checked the measurments and the OD is 5 1/4" but the diameter is still 5/8" I put my weight (285lbs) down on one of them and it yielded more than I thought it would; could this be made of a softer materiel than the OEM ones? Does spring rate depends on diameter or on the metal aloys the pring is made of. I wish manufacturers would stamp technical info on this things or at least the brand name so I can reseach it. :rant2:

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Good questions, and I'm always willing to help willing learners!

 

The metal alloy will affect spring rate, but when dealing with automotive coil springs, they are pretty much all of a similar enough alloy that it becomes a rather insignificant factor. It is usually assumed to be the same.

 

Keep in mind we're talking about spring rate here... A spring rate of 1000lb/in means the spring will compress 1 inch for every 1000 pounds you put on it.

 

 

The two geometric biggies affecting spring rate:

 

Wire diameter: Due to the geometry of a coil, the spring rate increases at a rate of the diameter change to the 4th power..... Yes, not linear, not squared, to the 4th power! That is why a .625 diameter is double the spring rate of a .52 diameter. Small change = big difference. Double the diameter, the spring rate goes up by 16x.

 

Wire length: This one will sound weird, but stay with me. The spring rate DECREASES an a perfectly proportional relationship to the overall wire length. The longer the wire, the lower the spring rate (softer spring).

The wire length is how long the wire would be if you uncoiled it.... For straight rate springs, the length is about pi*median diameter*number of coils. Pi is constant and the median diameter is pretty close to 4.7" for all pathy coils, so that is also pretty much a constant. Lo and behold, the significant factor is the number of coils!

That also means that if you cut a coil off, the spring will get stiffer. Honestly. 99% of folks don't realize that! So if you need to cut 2 or 3 coils off those long puppies to get them to a reasonable length, the springs will actually get stiffer. That is why el cheapo hack job ricer cars ride like they have no suspension at all - even if they're not riding on the stops. If you cut 1/3 of the spring off to make it 1/3 shorter, you are also making it 33% stiffer.

 

All that make sense?

Edited by mws
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Duuuuude way cool! :aok:

Thanks for the explanation, but I'm gonna need a little more explaning on the wire leinght afecting the spring rate. I can see this hapening when the spring is manufactured (to make a spring the same leinght with a shorter wire the coils will have to be further apart wich gives the wire a steeper angle making the spring stiffer) but I'm not geting how cuting a spring without changing the wire angle or the distance betwen coils afects the rate. I guess Ineed to get myself back to school too. Anyways, there will be a perfect oportuniti for experimenting when I install this springs.

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I think I can answer that. Lets say the spring sags .01" per coil when installed, truck stationary but sags an additional .01 per coil when driving over a speed bump. The spring has 10 coils so you have .1" sag from install and an additional .1" spring to absorb the speed bump. Cut the spring in 1/2 to 5 coils and it will only have .05" sag after install and .05" to soak up the speed bump before it reaches the same compression force.

You would be shorter and stiffer (less travel to the same compression force)... Get it?

 

I believe I said that correctly, eh Martin?

 

B

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Yes, I believe you have captured the effect....

The why has to do with the moment arm. Think of lever arms.

 

How to demonstrate?

 

Got it!

A coil spring is nothing more than a straight wire spring wrapped in a coil to keep it compact. With enough imagination, you can see it.

So find a piece of wire and play with it yourself.

 

Say, like a 1/4" diameter rod about 3' in length. Clamp one end in a vice, sticking out horizontally. Hang a heavy weight on the end - how far does it move?

Now cut it in half and hang the same weight. Or just hang the weight in the middle of the rod. It will only move about half as far. Since it moves only half as far for the same amount of weight, that indicates the spring rate is exactly double.

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So, If I understand you corectly, A spring that has the coils wound close together will be softer than a spring with the coils spread further apart so long as the two spring are the same leinght and have the same wire diameter?

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Same wire diameter, same coil height, but one has coils closer together?

In order to accomplish that, there would need to be more coils, right?

Which means longer wire length, so YES. Well done, Grasshopper.

 

Be careful, you now know more about coil springs than 99% of your friends....

 

 

Next lesson: Progressive springs!

Edited by mws
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  • 2 weeks later...

hi!!!

Que tranza compadres!!!

 

I want to lift my pathfinder...

 

the Cherokee front springs(installed in the rear of the path) and de upper control arms(for front end lift)(visit www.4x4parts.com to see the UCAs), will work for me??

 

Please tellme what can i do...

 

Tanx

 

Saludos desde Mexico cabrones!!!

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Yes, however I personally recommend Rough Country or Superlift UCA's (RC and SL arms are the same thing) because they more accurately correct the upper ball joint angles :aok:

 

And remember that the arms themselves to not actually lift the front end. You have to crank the torsion bars up to gain lift. The Arms, in the case of RC and SL (and Calmini) correct the suspension geometry, so that proper alignment is easier to achieve.

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  • 3 months later...
  • 4 weeks later...

I just got some tj lift springs to use on the back of my pathy they're 5/8" thick and all the other measurements match the jgc info taken from damagedreality site now i've just gotta stop procrastinating and install them

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  • 1 month later...

Another good option is to use the xj 3" lift springs from Rough Country Suspension PN 9262.

 

After cutting the pigtail off the coil stands 19" tall and they gave my '89 3.25" of lift. The spring rate is aprox 5% LESS than stock.(softer ride)

 

Because this spring is so tall compared to the other options Increased wheel downtravel can be had by running a longer shock than you could run with the other lift spings because the coil will not fall out.

Edited by MY1PATH
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  • 1 month later...

that's how I did mine. Since the cut end does not wrap narrow to the previous coil, making a flat surface, try it both ways and see how it fits best.

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Progressive rate springs have a tighter coil at the top than at the bottom, with the spring wire diameter at the top often being smaller as well. This allows the less stiff coils at the top absorb small bumps while the larger coils at the bottom can take more compression with a stiffer rate.

 

I already tried Ford Aerostar progressive rate coils in my Pathy...way too weak.

 

astarcoils1.jpg

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So here's the very long story behind my springs...

 

I'd been told to get JGC - V8 coils to acheive a 3" lift. Fair enough.

 

I didn't realize that it was the FRONT springs I needed to lift the rear! So upon ariving at the local JY I scouted out 3 JGCs. To my dismay they were all I6 so I nearly ended my search there. In hindsight this is a good thing since the REAR springs I would have wound up with would have been several inches too short! So I checked out a few other Jeeps. I stumbled on a 89 Comanchee and took a good look at the front springs in it, they seemed to be longer than the 'Finder's so I hauled 'em out.

 

I went over to a buddy's place to install them. My buddy's dad was visiting and has been a super-fancy welder guy, for lack of a more educated term, for around 45 years and really knows his stuff when it comes to metals. He tells me that because I chose a spring with a pigtail I made an error from the start. He says that to tamper with the spring by heating it makes it suceptable to breaking and cutting makes the spring sit unevenly and has potential to shift and or cut through the spring isolator even if chamfered since the last coil would no longer sit flat against the isolator. I took him on his word and he and my friend helped me weld up a shock mount that had torn off instead.

 

So I'm figuring the rear coils from a JGC - V8 must not have the pigtail.

 

I FINALLY check on here and find this thread.

 

Now I find out that not only is everyone cutting off the pigtail that seems to exist on all but the F-150 and Calimini 3" springs! I'm guessing there's been no problems with the affore mentioned issues?

 

I was stoked to see that spings for the Comanchee were listed as direct swaps for JGC coils, but the part number listed doesn't match up with any of the part numbers mentioned in the post refering to springs by both P/N and tag color.

 

The springs I picked up from the 89 Comanchee are a 9 coil spring and measure exactly:

18.75" tall (18.5" at the point at which the pigtail will need to be removed)

5.25" outside dia.

4" inside dia.

.545" thickness

 

Now that I've read this thread over and taken my measurements I'm excited to see what the results will be with such an unusual find. I'm working my day job and my night job tomorrow so the install is planned for friday. I'll post results and pics on Saturday.

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The bottom perch is stepped so the end of the coil can rest in it so I figured the flattest side should go up and so my cut end is down.

Also cutting just the pigtail is not going to create enough heat to relive the temper of the entire spring maybe only 3" from it at best if you use a cutoff wheel and none if your stubborn and use a hacksaw.

 

have fun with your comanche springs.

Edited by MY1PATH
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