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Old 02-27-2007, 07:21 PM
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moving rear coil spring location to change rate

I want to utilize the front coil springs from my F-150 donor on the back of my new project (early 30's sedan/delivery). My guess is the spring rate will be way on the high side resulting in a very stiff ride. So (being a penny pincher) I'm looking at my options for reducing the effective spring rate while retaining these "no cost" coils.

I know that installing the coils at an angle (from perfectly perpendicular to the axle) will reduce the spring rate as shown in this link http://www.proshocks.com/srshocks/tech4a.htm However, I think these rather bulky coils would look strange if they were tilted (I'm also concerned about how they would "ride" in their seats).

My next through was to move the springs further inboard (closer to the center section). I'm assuming this would reduce the effective spring rate "at the wheels" as the coils are moved further away from the wheels. (I could be wrong about this but it just seems to make sense to me.) Is there a simple mathematical formula I could use for the effect of moving the springs inboard? For example, if I moved the spring to a point half the distance between the original spring mount position and the axle center section, would I reduce the effective spring rate by 1/2?

[BTW, I checked a number of the threads and related links but could not find info related to the effects of repositioning springs in this fashion.]

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Old 02-27-2007, 07:53 PM
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Angling them will change the effective rate, but moving them inboard and keeping them perpendicular to the load will make the body roll more, but won't change the effective spring rate unless you are doing an independant rear.

If you were to make a trailing arm and move the spring closer to the pivot point you would reduce the effective spring rate.

IIRC the formula is a linear one, If you have a 500# load and use a 500# rate spring directly between the axle and the frame, it will compress 1"

If your trailing arm is 2' long, moving the spring 1' closer will make the 500# spring move 2" , cutting it's effectiveness in 1/2, so it now has a rate at the axle of 250#.

Willys36 and Billy Shope helped a guy out a while back, they posted some good calculations, (real ones), for figuring that stuff.

Here it be
How mutch for free

Hope this helps,
Mikey
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Old 02-27-2007, 10:58 PM
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Mikey,

That thread you linked came up during an earlier search I did and it sort of had my head spinning. Anyhow, I think you answered my question about moving the springs inboard...it's a bad idea and it won't accomplish what I want.

Back to the drawing board.
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Old 02-27-2007, 11:20 PM
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Quote:
Originally Posted by cboy
Mikey,

That thread you linked came up during an earlier search I did and it sort of had my head spinning.
Back to the drawing board.
I know, when they started talking in calculus I left the room

Mikey
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Old 02-27-2007, 11:58 PM
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Dewey, You could do a bellcrank with push rod deal and adjust the spring rate that way..would be really cool with inboard springs and shocks..that woudl take care of the leverage situation as well as having hidden springs and shocks..

Just a thought

Sam
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Old 02-28-2007, 02:13 AM
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Or you could set up a trad Ford wishbone with one spring up front like a motorcycle monoshock. It'd need some serious locating at the rear of course.
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Old 02-28-2007, 02:33 AM
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moving both spings inboard will reduce the spring rate when one tire coues over a bump, such as a small pothole, but the full spring rate will still be in effect when both tires go ever a bump (speedbump)

installing the springs at an angle realy only works on coil overs, as the pivot action at the upper and lower bolts makes sure the spring is always being compressed properly

only way to realy change the spring rate of normal coils is either

a) bellcrank setup
b) installing the springs on a lower control arm forward of the axle (which results in the suspension needing more distance to max out)
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Old 02-28-2007, 08:20 AM
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Quote:
Originally Posted by OneMoreTime
Dewey, You could do a bellcrank with push rod deal and adjust the spring rate that way..would be really cool with inboard springs and shocks..
I've never done anything with a bellcrank. Is there a "backyard" (read cheap) solution to the bearing question? I could make the bellcrank itself out of plate steel I would think, but the bearing(s) in the pivot holes would be a concern.

Anybody got any pics or links to folks how have fabricated their own backyard bellcranks and bellcrank systems. (I've seen the high end expensive set ups...I'd be looking for how someone has done it with Tractor Supply or Fleet Farm parts.)
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Old 02-28-2007, 08:27 AM
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Quote:
Originally Posted by lowROLLERchevy
installing the springs at an angle realy only works on coil overs, as the pivot action at the upper and lower bolts makes sure the spring is always being compressed properly
Thanks for the warning LRC, that sure saves me the work and frustration of a failed attempt at tilting the coils. (Scratch THAT one off my list.)
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Old 02-28-2007, 08:43 AM
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If you use a bronze bushing as the pivot I think that would work fine..if well greased bronze bushings last a long time..Make the bell crank itself from two pieces of 1/8 steel with some spacers between should work out..The bronze bushing may be available from tractor supply or one of those kind of stores..

Sam
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Old 02-28-2007, 09:04 AM
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Quote:
Originally Posted by lowROLLERchevy

installing the springs at an angle realy only works on coil overs, as the pivot action at the upper and lower bolts makes sure the spring is always being compressed properly
I disagree.


If the seats that the coil springs nest in are parallel and perpendicular to the direction of travel of the spring, why would the effective rate not change.

It's still physics.

You are still moving one end of the force (spring) closer to the pivot, (fulcrum), and thereby increasing the mechanical advantage that the load,(weight of car), has over it.

Dewey is fabricating his own suspension. He can make the spring seats so they will allow the spring to sit square to the load they are holding up.

BTW, Sam has a great idea
Later, mikey
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Old 02-28-2007, 10:41 AM
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FYI..I should have called it a bearing not a bushing..two different things..

Anyway to make one of those things one takes a piece of pipe or tubing large enough to take the OD of the bearing and reams it to fit..then he reams the ID of the bearing to fit the shaft..Drill through the housing and bearing and tap the hole for a grease fitting and that when properly sized will last a long time...we have only been using bearings of that nature for about 200 years that I know of so they are known to work quite well for certain things..they are a press fit when properly made and fit the shaft with just enough clearance so the shaft turns smoothly..

By manipulating the distance from the shaft centerline to the pivot points of the bellcrank the spring rate can be altered..just some simple mechanics of leverage..

Sam
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Old 02-28-2007, 11:31 AM
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Mikey,

Here is a very crude drawing...but is this what you meant by keeping the mounting surfaces parallel and perpendicular to the spring load? Anything else I ought to be aware of if I DID try this setup? (certainly seems like the least expensive - although under ideal condition I would like to be able to adjust the tilt on the spring so that the "ride" could be fine tuned (like with an adjustable coil over)...hmmmm, have to think about that one a bit.)

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Old 02-28-2007, 11:55 AM
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Quote:
Originally Posted by powerrodsmike
I disagree.


If the seats that the coil springs nest in are parallel and perpendicular to the direction of travel of the spring, why would the effective rate not change.
if both springs are closer to the center of the axle, and only one tire moves up over a bump, your axle has leverage on that spring, causing the effective spring rate to be lower

if BOTH tires move over a bump in the same situation, the axle wil NOT have leverage on either spring, so you have the original spring rate in effect

picture 2 coil spings under an I beam, if you push down on the entire i beam at once, you dont have leverage on either spring, so weather both springs are in the middle, or 10 feet apart near the ends, it doesnt matter ... full spring rate

on to the on to angled springs :

and heres a crude drawing of what happens with angled coil spings under heavy suspension travel .... notice the staight line betwen the "perches" ... it skews when the springs are compressed ... which could lead to a broken spring, or the spring removing itself from the perch
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Old 02-28-2007, 11:58 AM
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That is how I would go about doing it if I wanted to make a set of coils have a less effective rate.

Keep in mind though that you will have more body roll.

In all realitythough, with the HUGE difference in spring rate of the front of that f150 and what you will need to hold up the back of that sedan, you are bound to be dissapointed where ever you put those springs.

I'm guessing that those front springs are in the 1000# range and you will need more like 150#

That will take alot of mechanism to get those springs to work, probably offsetting whatever savings you will enjoy from not buying some springs closer to what you need..

Later, mikey
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