Leaf spring old school

[geometryjeff]

New to site; Hi to all and Happy New Year. Trying to improve leaf spring geometry on 68 Camaro. I'm machining new front cups to allow about .8" move outboard per side; with the 1 1/2" per side move inboard at back, this will keep springs more parallel and flat with centerline of car. I've welded seams and welded framerail plates at front perch area for mounting solid and to anchor the rear of the frame connectors. This should help take load and secure a fixed position of the rear end and give lateral support for leafs. Any thoughts? Oh yeah - I know the newest technology is better, but I'm old school - except better with age.

[exwestracer]

Are you ditching the rubber "sandwich wraps" between the spring pack and axle housing?

[Rod]

The old school leaf springs work great! what leafs are you using? I use the hotckis leafs 1.5 drop with 1 inch block, and the spherical leaf bearing upgrade, I used the 3 inch leaf early on and that lowered the ride center of the car to far and made it push in the corners

[High Plains Mopars]

I'm machining new front cups to allow about .8" move outboard per side; with the 1 1/2" per side move inboard at back, this will keep springs more parallel and flat with centerline of car.

I'm unfamiliar with 1st gen spring geometry, but if you are taking splay out of the leafs and making them more parallel, you may be inducing more roll steer with the rear and you will have added more oversteer to the vehicle once complete. This certainly can be balanced with other components, but just an FYI about the move.

Nothing wrong with leaf springs on a multi-duty application.

[Rod]

Trying to improve leaf spring geometry on 68 Camaro. I'm machining new front cups to allow about .8" move outboard per side; with the 1 1/2" per side move inboard at back, this will keep springs more parallel and flat with centerline of car.

the triangulation on the rear leafs helps turn in on the car and stright line tracking for higher speeds, and helps with lateral location for the axle, you should leave it there, Parallel leaf springs really are not Parallel in the car,....dont take the name so Literal

[geometryjeff]

Yes, rubber is gone and I also have Hotchkis 1 1/2 drop springs with spacers cut for 3 degree pinion angle. I installed Al front bushings with Delrin liners to tighten squishy in front and will do the same in back with added lubricant provision. About the triangulation aspect - I'll do some more studying of Maurice Olley's works. Thanks for input.

[geometryjeff]

OK; this is what I have learned from my studies ("Chassis Design Principals and Analysis"). The leaf set up is referred as the Hotchkiss rear axle. From the book: "Generally the Hotchkiss rear axle is free from any tendency for the axle to yaw when pushed laterally. This is true if the springs are parallel and if we ignor the roll steer effects. It is not true where the springs converge forward as shown.... In this case there is evidently a lateral deflection oversteer." There is also mention that by converging springs toward the rear, the expected result is lateral deflection understeer; but no data was given. With respects to the angle created by a line between the axle and the front spring eye and a line on the ground, it is perferred to have the angle slightly pointing down toward the front of the car for a rear roll understeer condition. Granted, this science is 60 years old, but isn't science, science.
My goal is to have several points of adjustment in the rear suspension and spend some troubleshooting time behind the wheel (in a safe environment - not any side street). Studies also have been done on rear suspension geometry effects on braking which are equally important to the total package. Thanks for all the input. I'll post results when I get there.

[protouringorprostreet]

Al Jimenez runs 6s at over 200 mph on leaf spring.( useless trivia of the day)

[Thephranc]

So you could take a set of leaf springs and say the front spring mount could be located on a screw type set up or cam system that you could in theory use to adjust leaf settings for tuning over/under steer?

[SLO_Z28]

So you could take a set of leaf springs and say the front spring mount could be located on a screw type set up or cam system that you could in theory use to adjust leaf settings for tuning over/under steer?

This is more common than youd think. I know of at least one company coming to market with a product that does that very soon. I have modified my cars pickup points in a similar fashion as to what the OP is doing. Before you think its worse than a 3-Link or 4 link, sit down and do the math, you'd be surprised that most aftermarket packages are at best no better than the factory setups.

[High Plains Mopars]

This is true if the springs are parallel and if we ignor the roll steer effects.

Notice the caveat - if we ignore the roll steer effects. Roll steer is present in an arched leaf spring as you load and unload the pack and alter the corresponding wheel base length based on those changes. You can minimize or alter the effects by using a nearly flat spring and mounting splay. It is just another variable in the layout. You might check out the Afco tech articles on leaf springs as well.

So you could take a set of leaf springs and say the front spring mount could be located on a screw type set up or cam system that you could in theory use to adjust leaf settings for tuning over/under steer?

Sounds good, but, simply moving the front spring mounting location in/out can produce a bind as the the axle housing and rear eye also locate the spring. Moving the front spring eye in 1" may require moving the axle mounting pin .375 or more in the corresponding direction to maintain alignment and reduce binding.

[Thephranc]

Could you make the spring a slotted section for the pin to fall into and instead of a static pin use a bolt in a female threaded sleeve that you can torque down to secure and get your alignment at the axle that way?

Just thinking out loud so to speak but I find this kind of fascinating.

[Rod]

OK; this is what I have learned from my studies ("Chassis Design Principals and Analysis"). The leaf set up is referred as the Hotchkiss rear axle. From the book: "Generally the Hotchkiss rear axle is free from any tendency for the axle to yaw when pushed laterally. This is true if the springs are parallel and if we ignor the roll steer effects. It is not true where the springs converge forward as shown.... In this case there is evidently a lateral deflection oversteer." There is also mention that by converging springs toward the rear, the expected result is lateral deflection understeer; but no data was given. With respects to the angle created by a line between the axle and the front spring eye and a line on the ground, it is perferred to have the angle slightly pointing down toward the front of the car for a rear roll understeer condition. Granted, this science is 60 years old, but isn't science, science.
My goal is to have several points of adjustment in the rear suspension and spend some troubleshooting time behind the wheel (in a safe environment - not any side street). Studies also have been done on rear suspension geometry effects on braking which are equally important to the total package. Thanks for all the input. I'll post results when I get there.

we gonna learn some thing