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Shackle length ?'s

BAPerf

Well-Known Member
Shackle length ?\'s

How can I determin the correct length shackle to make/buy?

This will be on a Toyota with a rules dictated 14" max. on travel. Can the stock length spring be finessed to 14"? Would a longer spring have an advantage if the factory front pivot to axle distance is maintained?

Thanks,

Brian
 

drtdevil93

Well-Known Member
Re: Shackle length ?\'s

more info- what toyota? year make...

a stock 89-95 toyota has about 11" of travel in the rear, but with the overload in it wont work right. you can modify the stock spring and get about 12-13" travel, and it will work pretty good. the weakness would be the stock main leaf (toyota spring steel is pretty brittle). you could also get a custom spring built to go in stock location, this should get 14-15" travel, work good, and last pretty well.

if it is a 98+ tacoma then the deaver f42 production spring will bolt right in and give you 14" travel.

now to your shackle question. its important and makes a big difference. you need to measure the growth of the spring. with the spring off the truck measure from the center of the front eye along the curve of the spring to the rear eye. next measure straight from eye-eye. now subtract them. this is the amount of growth. that number is the shortest shackle length that will work, the longest it should be is about 2" more than that.

THIS ONLY APPLIES TO THE SWING UNDER TYPE SHACKLE (toyota). THE SWING OVER TYPE (f150, chevy, mod. ranger)IS DIFFERENT!

and remember with a longer shackle you might be increasing negative arch at bump, which can be a bad thing. i cut uptravel off by spacing the bumpstop down sometimes to make the spring last longer, but this depends on what kind of spring it is.

good luck

erik
 

ntsqd

Well-Known Member
Eric, can you expand on how the swing over type length would be determined?
 

BAPerf

Well-Known Member
The truck in question is an '84 Toyota 2-wheel drive.

The spring length is ~51.5" eye-to-eye as far as I can tell. I'm guessing that a shackle length of ~ 8" should work.

Back in the SODA days, Johnny Greaves used to cut the end of the frame rail at an agle so that the spring/hanger would contact the frame just before bottoming out the axle. It appeared that it would shorten the effective length of the spring under full compression, thereby increasing the springrate under the last couple of inches of compression (~2").

Since the truck is only going to be used for short-course action, is spring life a great concern?

Thanks,

Brian
 

drtdevil93

Well-Known Member
ntsqd said:
Eric, can you expand on how the swing over type length would be determined?
why sure! i just did one today, so its all fresh in my can of worms.

how to figure out correct shackle length for a swing up type shackle: first the 2 extremes- at full droop the shackle should be horizontal, or even a little under. you then have to limit it with straps to just above horizontal. the other extreme (bump) is debatable. i personally do them so the shackle is about the 1'oclock position. i have some *odd* theoretical ideas about why this is preferred. so there is about 120 degrees of shackle movement you want. now you'll take the growth of the spring, and figure it from there.
lets say we had a growth of 8 inches.

8(growth)*3 (120 degrees is 1/3 of a circle, so multiply by 3 to get circumference) = 24". now you solve for radius: 24/ 3.14 (pi)=approx 8" diameter /2 = 4" radius. NOW TO SIMPLIFY THAT EQUATION A BIT: just take your growth number and divide it by 2. a little simpler, but i think you should understand an equation in order to use it correctly. so a spring with 8" growth needs a 4" shackle. a spring with 10" growth needs a 5" shackle. and so on. this is only if you subscribe to my shackle angle part.

ive seen a lot of trucks with long shackles and the suspension doesnt want to fall out simply because there shackle is too long. with a swing-over shackle, you dont need, and dont really want a very long shackle. the longest ive ever seen used correctly was on pete albanos ranger, and it was i think 7.5" long (that was a very big spring). im sure people have heard of the trick on rangers, instead of just flipping the mount you move it back an inch or so and you pick up nearly 3" more droop. and its free!!

erik
 

BAPerf

Well-Known Member
Erik,

The Toyota I am playing with is an '84, to be used at ROR and other short course tracks. The lengths I am coming up with are ~51.5" around the arch, 44.5" between eyelets when the shackle is unhooked. I am guessing that an 8" or 9" shackle would be about right.

Is there a correct angle for a swing under shackle at droop and/or bump? From what others have told me the last bit of droop travel is hard to get with a somewhat flat spring. Would it be bad to try and set-up the shock as the limiter, with the spring able to drop 1-2" past the extended shock (if the shock were unhooked)?

Thanks,

Brian
 

drtdevil93

Well-Known Member
you are right for the length. as for the angle id set it up so the shackle is in the 4oclock position at bump. the easiest way to set this up is to measure from the front eye, and use the 51.5" you came up with.

erik
 
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