Shackle Lengths...what do I have???

[LakeNorman_FJ40]

What size are stock shackle lengths??? Also, thoughts/opinions on the following...

In an effort to resolve wandering steering issues, I'm getting ready to replace my spring/shackle bushings (already working on the center arm housing replacement too to solve what I think is most of the steering issue...so no need to point that out).

Since I'm going to be replacing the worn shackle bushings, I might as well consider shackle upgrades while I'm already removing/re-installing these parts.

Oh, my suspension is **I think** a BDS lift...not sure if 2.5" or 4", but the shocks are defintely BDS (was installed by PO). No caster correction shims are currently installed. I'm running 33/12.5's MTRs on 15" wagon spoke wheels...this set-up does not rub in the front or rear except in situations of extreme axle articulation.

Here's what I have in terms of shackles:

FRONTS
- appear to be basic flat stock steel shackles
- 3" center-to-center bolt distance (total shackle length of 3.5")

REAR
- definitely not stock
- 5" center-to-center bolt distance (total shackle length of 5.75")

Just trying to figure out what I have... The rear sags just a little compared to the front after I installed the **heavy** MAF rear tire carrier...and will likely sag more once the hardtop is installed. So another reason to consider shackle options at this point.

 

[Fast Eddy]

REAR
- definitely not stock
- 5" center-to-center bolt distance (total shackle length of 5.75")

The rear sags just a little compared to the front after I installed the **heavy** MAF rear tire carrier...and will likely sag more once the hardtop is installed. So another reason to consider shackle options at this point.

Sounds like you need new rear springs, at a minimum. It sounds like you may even have 4" front and 2" rear springs based on the extra long shackles and the sag.

 

[LakeNorman_FJ40]

Maybe the "sag" is in my head...in looking at my pics again I realize that one is full-loaded with gear for the weekend and the other is unloaded. Duh.

So it looks like they used an extra long rear shackle to level the truck back out.

What's the longest rear shackle that I can run without getting into driveline issues? Or am I already at the max length?

 

[3DAMAN!]

Nice ride!

 

[zuluzeugma]

From the looks of your pictures you have horrible rear and mediocre front shackle angles. Take some close up pics of each for a better determination. Your shackles are plenty long enough already (really they are too long for your hanger locations). You need to adjust a few things and your ride quality will improve dramatically.

Sick truck though... looks good

 

[Pin_Head]

Any time you change the shackle length, you change the differential pinion angle and on the front you change the caster. Wandering is often a problem with caster. Your local alignment shop should be able to measure the caster. If it is not +1 degree (or more), then caster shims are needed.

Lenghtening the shackles is not an effective way of correcting sag because the sag is due to the spring rate being too low for the vehicle weight.

Shackle angle has very little to do with ride quality and effective spring rate. The effect is very dependent on the spring shape and for flat springs, a angled shackle has a negative contribution to spring rate and ride softness.

Shackle angle and length is very important for suspension articulation and again this is very dependent on spring shape.

 

[Brian in Oregon]

If you want to prevent sag when your FJ40 is loaded with people and cargo, it should sit with a slight 'rake' when empty. Meaning the rear should be slightly higher than level compared to the front.

Also, any height gain from a lift shackle will be HALF of its extra length over stock. For example, a 3" lift shackle moves the spring eye 3" further away from the frame, but the axle is in the center of the spring, and thus would move it only 1.5".

And there is a definite limit to how much you can lift a spring. First, shackles too tall make the suspension wobbly and squirrelly. And at some point, particularly with worn out springs, they stop lifting, go flat, and then even reverse arch.

 

[LakeNorman_FJ40]

Zulu: Thanks. Interesting in that you say the front shackles are mediocre and the rear shackles are horrible...I thought it would be the other way around. Are you saying the rears are way too tall? The ride isn't all that bad...what suggestions are you referring to improve the ride?

Regarding the sag, you can see that the truck is level when unloaded. Loaded, it's barely noticeable (can you tell I'm a perfectionist??? ), so let's not worry about that right now...let me get the hard-top installed sometime in the future and then see if I have a spring issue.

PinHead: Yes, I need to just get the caster checked. Can you confirm my front shackles are stock length (3" center to center on both shackle bolts)? At first I was thinking part of my steering problem was needing caster correction shims, but now I'm wondering if the truck is still running stock front shackles and doesn't need the shims???

Brian: Yes, squirrely is a good way to describe how it drives. Down the freeway is a white-knuckle experience trying to avoid grooves and irregularities in the road surface as the truck wants to follow the road. Stopping quickly just seems to aggravate the steering issues further. The rear tall shackles can't be doing this...so I was thinking the front shackle bushings might be contributing to the steering issues.

So back to the shackles...

Here's one of my rebuild pics with a decent shot of the rear shackle:

In this pic, you can get a better view (not the best view) of the shackles. Note the driver's side one is twisted slightly and it looks like somewhere down the line someone over torqued the bottom of the driver's side shackle.

 

[zuluzeugma]

If you put a magnetic angle finder on the side of the shackle you should see 45 degrees + or - 10 degrees. Some will argue that they have theirs setup some different way and there's are awesome...; however, if you think about the kinematics of whats going on it makes sense. The purpose of a shackle is to allow drop/compression of the springs. With your shackles almost totally verticle, the springs cannot drop out at all. With a 45 degree angle, they can drop/compress to their maximum potential.

 

[Pin_Head]

With your shackles almost totally verticle, the springs cannot drop out at all.

Not true.

It is the eye-to-eye distance of the spring that determines the shackle swing. When the spring flexes, the eye-to-eye distance changes.

 

[BC40]

As to the shackle lengths, the older 40's used a 2.75" pin to pin, while newer trucks (all the 80's cruisers I believe) like yours were 3.5".

So your rears are extended for additional hieght.

I think with the hardtop on and loaded it will be squatted down in the back, but that's not necessarill wrong. If you increased the spring rate (with additional leafs), you would likely be unhappy with the ride quality empty. Hence the comment that it is better to start with a setup that has a slight rake empty.

If there are no driveline vibrations with those shackles and you're happy with the ride quality, I'd say leave it. Looks good.

 

[LakeNorman_FJ40]

Thanks Martin. Exact info I was looking to find. I think for now I'll just replace the front shackles with the same stock size but a little more heavy duty design and leave the rear shackles alone (but straighted out) and install new bushings all the way around.

Between not being able to fit the 40 in the garage combined with driveline vibrations, the little bit of extra height just isn't worth it.