Outer Limits 4x4 Board

seeing as i'm a noob (be nice) and i'm about to do my suspension lift, can anyone explain what shackle angle is all about?
I've got a 87 NT zook and got 3 inch trail gear springs to go on, but i;m not sure whether to get some extended shackles to go with them, nothing major just 1inch over stock (so only 5mm of lift approx) either that or replace them with new stock ones...i've got 31's on old f100 rims to go on (15x8's) so should i bother with the shackles as well? and how do i know what sort of angle to set them too? the same as the stock ones??

G'day Chopz.

Without fabrication, you can't really "set" shackle angle - it is what it is for a given length of spring and lift height.

However, adding longer shackles will make the shackle angle steeper, all other things staying the same. Steeper (i.e more vertical) shackle angles aren't really desirable, but they may be a by product of how your suspension is set up. I'll explain.

The more vertical the shackle becomes, the less droop you have in the suspension - there's almost nowhere for the spring to go. With 3" lifted springs on a sierra and stock shock mounts and bumpstops, you're not going to have any droop to speak of anyway- the shocks will be close to fully extended at ride height. Adding longer shackles at this point won't have much effect on anything.

Stock shackles were designed to work with the stock spring length and stock range of motion. If the new springs are significantly longer than stock (not "taller" but longer eye to eye) then you might find the stock shackles too short to allow full compression in the suspension - the shackles will hit the chassis or invert before the axle hits the bumpstop. There's definitely a case for a longer shackle then.

However, with genuine 3" lift springs, it's unlikely you could reach the bumpstop (particularly in the rear) in any case, and with a plan to run 31's, you might benefit from some bumpstop spacing.

You need to be aware that running longer shackles in the front ALWAYS results in a reduction in steering performance - the car will not track as well, the steering won't self centre as well, and turn in won't be as crisp. This is because of a reduction in caster.

As you can see, it's really a suck it and see exercise. It's very dependent on the individual setup of your car.

A coupe of other points - when you pull leaves out of your 3" springs to get an acceptable ride, you will loose height and you might end up with a very flat (i.e horizontal) shackle angle. A little bit longer shackle will remedy this quickly and easily. Under those circumstances, a longer shackle won't have much negative effect on the front end either.

A flatter shackle angle results in a softer initial "hit" in the suspension. If you compare two cars with the same springs, but one has vertical shackles and one flat shackles, the flat shackled car will ride softer and will tend to weight transfer ("squat") more under power.

As you can see, it's a balance of competing factors. It's unlikely stock shackles are idea for your springs, but then longer shackles by themselves won't provide much gain (in the rear) without other fabrication work, and will negatively effect handling (in the front).

Steve.

I just typed out a very simillar response, but you beat me Steve (damn work). Basically what he said ^^^^^^

Layto....

Ok thanks for that Steve.
So would i be correct in saying a should fit my springs first, then measure to see what length shackles i require??
I will be gettin new shocks but wanna get the springs and shackles fitted, then flex it up to measure what sort of shocks i need. I also had a RTC steering dampner to go on....will this help with steering in case i do need to run extended shackles?
Will i need to remove leaves from the springs or will they eventually get softer.
I'm just trying to get proportion right is all, dont want it too high coz it will be too tippy but of coarse i want good flex.
If any part of what I'm doin is wrong then shut me down and let me know..

If you haven't read it already, have a read of this:

http://www.outerlimits4x4.com/phpBB2/vi ... 97#1147697

In short, the springs won't get "softer" as they age, but you may loose some height over time. I don't think there's any point in running 3" leaves in a sierra. I'd pull a leaf or so until they flatten out. 40-50mm of total lift seems heaps. Generally, that's plenty of lift to have acceptable compression travel, even once the bumpstops have been lowered to help tyre clearance.

Try your springs with stock shackles, let them bed in and settle, then, if you're still unhappy with the ride ( my guess is you will be) then pull some leaves. Don't worry too much about the height, there's no relationship between height and flex (really!) If the shackle angle is marginal and looks like it's costing you droop, and assuming you have enough shock travel to use the shackle length, then you can then investigate shackles.

Remember though, there's almost no scope to increase shock travel without fabricating new mounts and/or spacing your bumpstops.

Steve.

RTC dampers won't fix a lack of caster due to shackle length.

I use to have Calmini 3 inch springs, stock shackles and two inch bumpstops it use to clear 31's just fine, flex was fairly average though.