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Leaf Spring rear Shackle Length

Shocks, Springs, Brakes, Frame, Body Work, etc

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j-c-c
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Leaf Spring rear Shackle Length

Post by j-c-c »

In the 60's 12"(?) long rear shackles were all the rage on the street inspired by Nascar stockers, mainly for looks/rake.

It was a passing fad, and never heard a great deal about any handling performance downsides.

My question here is, what are the downsides of using a shorter then OEM shackle to slightly change the leaf spring orientation, without resorting to lowering blocks/sliders?

As long as there appears to be sufficient range of motion needed, and shackle doesn't go into a "locked" forward position, what harm/downside is there by building/using a shorter shackle?
Protech Racing
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Re: Leaf Spring rear Shackle Length

Post by Protech Racing »

The angle of the spring under deflection determines the axle shift . If the front is lower then the rear, the axle toes in as that side is depressed .
Other than shifting this angle, no problem .
dannobee
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Re: Leaf Spring rear Shackle Length

Post by dannobee »

What is the object here? To lower the car?

If so, you can accomplish two things by raising the front leaf spring mount. 1, the body/frame gets lowered. 2, you gain anti squat. likely getting back as much as you lose by lowering the car. The pinion angle can be adjusted to where you need it with wedge/angle shims.

Depending on how it's mounted, you might have to do some fabrication or hit the wrecking yard to buy another pair of mounts and make one mount out of two to relocate the front eye bolt higher.
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Re: Leaf Spring rear Shackle Length

Post by j-c-c »

Main purpose here is to get the front leaf portion closer to level, to negate roll induced oversteer. The current composite spring has at rest too much arch, partly because of weight reduction of the car over time. The front eye is as low currently as possible. Raising the rear eye/shackle would help with my problem, hence the shorter quick fix shackle idea posed here. This is not a drag application. Lowering the car is quite acceptable as a side benefit. I can dial in maybe more rear wing DF to reduce some existing arch, but balance then goes out the window as I'm not likely to be able get needed front matching DF.
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Re: Leaf Spring rear Shackle Length

Post by Protech Racing »

Depending on rules.. I am developing a 3 link plus track bar for my required leaf spring car . So, I'll have 2 lower trailing arms and an upper torque control arm . Along with th e track bar . The leafs are required for my rules but will simply hold the axle up and not control the toe.
This way I can angle the trailing arms to control dynamic toe.
I looked around and can not find anything similar. Coil or air bags are normally used.
I use really soft springs as a rule and like some toe out for the rear on smallpower cars. Keeps the fronts working better.
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Re: Leaf Spring rear Shackle Length

Post by dannobee »

Going back to what I said initially, do what you can to RAISE the front spring eye. Relocate the mounting hole in the frame/body. If they're like early camaros, there's a bracket that bolts to the body that you can modify. That will give you the twofer of helping reduce oversteer and will lower the car.

The front half of the leaf spring (from the front spring eye to the center of the axle tube) is the equivalent of your lower links of a 3-link. When we were limited by rule to leaf springs in fabricated circle track cars, we'd choose a gen 2 camaro front clip and leaf springs in the rear (by rule the front clip had to match rear suspension setup). Instead of using the stock camaro or composite springs, we'd use the landrum chrysler style springs with extra leaves on the front half to help reduce wrap-up/spring flex.

Maybe Landrum can give you some ideas.

https://landrumspring.com/technical/ova ... ing-point/
j-c-c
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Re: Leaf Spring rear Shackle Length

Post by j-c-c »

Thanks, maybe I wasn't clear enough. The current composite spring has an upward front arch at rest. That promotes oversteer in roll ( toes out). I have lowered the front eye as mentioned, as much as practical. Raising the rear eye achieves the same basic result, but proportionally will be less improvement, because rear leaf segment is slightly longer then front segment. I don't need much improvement, but anything I gain, will be worth it at this point.
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Re: Leaf Spring rear Shackle Length

Post by Protech Racing »

Raising the front mount increases toe out . The wheel base gets longer with deflection. Useful for oval trackers ,often with spring mounts different from side to side.

Anything that softens the rear will aid your situation . For the plastic ( Corvette) springs, I have ground them a little . Carefully with a belt sander , outside with large fan.
In addition, adding a low mounted track bar and using very soft rear spring mounts will allow the roll to be controlled by track bar height . Basically you want the track bar locating the axle, not the springs . This is a huge improvement over hard mounted rear leafs or sliders . This moves the roll center form the average of the leaf mounts to the frame mount of the track bar .
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Re: Leaf Spring rear Shackle Length

Post by j-c-c »

We are on the same page, any outside wheel toe out promotes oversteer? Opposite of my goal.

Sanding the springs I had considered. Never hear of anyone doing it. I probably would replace the springs first, if I could get Hyperco to custom arch a new composite set of springs for me.

A track bar now, because of space, fuel cell, diffuser, exhaust routing, etc is not an option unfortunately.

I've got an IRS on the bench for next car,

Car after that will be a 3 link with watts or track bar, haven't decided. :lol:
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Re: Leaf Spring rear Shackle Length

Post by Protech Racing »

I have never run a leaf car without a track bar for this reason. All of the cars that I have set up , improved enough to prioritize the track bar in front of the diffuser. You gain by lowering the roll center 6-12in in some cases . Adding lots of rear grip . Look further into it . Go faster.
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