Gap on Top of Rear Leaf Spring Ends ?

[RobsZ06]

Hi all,
I looked at the forum's suspension pics, but none showed this (not even the 'lowering' pics).
Mine isn't lowered, that I know of - its used.

My 02 Z06 has about an inch gap on top of each leaf spring end, with just a little bolt keeping it screwed in ? I'm guessing that's the bolt used to lower the car, but it can' be all that holds that leaf on !

Is there something screwey here ? Seems like an invitation to lateral motion or a snapped bolt ?


Opinions ?

[RobsZ06]

Oh, and also...
Folks talk about lowering the Front...its always 'turn the bolt counterclockwise, then back of 1/4 turn'...
Mmm, it seems to me that turning that bolt counterclockwise would remove it ? I'm a little curious about how far do I back it out, before it comes out of the nut ?
The DYI wasn't very helpful on the Front...

[No Doubt]

A good practice is to leave at least two threads showing through the nut. I turned mine 6 turns at each corner and that left a few threads through the nut. I made a mark on the threads and nut so I could lower each corner the same amount.

That was before I had it corner weighted with scales and aligned. I'm not sure how much, if any, he adjusted them at that time. I asked if the height was ok and he said it was just where he'd have set it.

[pmontelo]

Rob, here is a link to another DIY with a little more detail, maybe this will help. FYI, the bolt doesn't hold the leaf spring on, but it does connect it to the lower control arm.

DIY Lowering Without Frank's Mechanic (lots of pics)

[RocketSled]

Originally posted by RobsZ06
...I'm guessing that's the bolt used to lower the car, but it can' be all that holds that leaf on !

Is there something screwey here ? Seems like an invitation to lateral motion or a snapped bolt ?

I love answering this kind of stuff....

The rear suspension of your Z06 is a fully independent type. The driveline (the Differential) is anchored to the chassis, and power is delivered to each wheel through "Half Shafts", which function as axles, one for each wheel. The inner and outer ends of a Half Shaft are attached to the differential and to a wheel hub, respectively. The coupling is made using Constant Velocity, or "CV" joints (sometimes called "Universal Joints", though they are not the same things, they're only similar).

You need this arrangment because each rear wheel is allowed to ride up and down independent of the other wheel, and this causes the angle between the differential and wheel hub to change. The Half Shafts, like any other axle, can't bend. CVs allow the Half Shafts to twist freely when the line between the inner and outer attachment points (differential and hub) is not straight/horizontal.

The wheel's up/down travel is regulated by two linkages, and Upper and Lower Control Arm (1 each, each side). Each Arm is anchored at two points, to the chassis at it's inner end, and to the wheel hub at it's outer end. The inner end is free to rotate on a pivot (like a door hing). The hub is mounted on a similar pivot at the outer end.

If there was only one arm, say a Lower Control Arm, the wheel would sweep an arc shaped path as it moved up and down (this was the critical design flaw in the Corvair rear end, BTW). But because the arrangement of pivots and arms on the Corvette creates a trapezoid (rectangle) shape, the motion is constrained and the wheel rides up and down almost perfectly vertically.

The control arms also control lateral load. The distance between the center of the chassis and the center point between the left and right wheels always stays exactly the same. (this is the function often performed by a "Anti Sway Bar" in a "live axle" rear suspension. Corvettes actually have "Anti Roll Bars", which transfer vertical load, not lateral load, from one side of the car to the other to help reduce body roll in a turn). Unlike in a leaf-sprung rear end, the spring in a Corvette rear takes no lateral load whatsoever.

This design is a good thing. It means that as the car rides up and down on the suspension, or the suspension rides over bumps in the road, the suspension geometry (it's alignment) stays close to the ideal at-rest settings. You get good, stable, predictable handling as the car takes different "sets" as it travels down the road.

The leaf spring is mounted to the same fixed point as the differential. It is free to move vertically (one could say "flap") at the free ends, and fixed at the center. The free ends of the spring are attached through a link (the "Bolt") to the lower control arms. The weight of the chassis pushes down on the spring center, that load is transferred to the ends of the spring. The lower control arm transfers that load through the hub to the tire and then to the ground. The ground "pushes back" on the tire, hub, link, spring and the spring's free end bends upward under the compression to take up the load.

Because the suspension's control arms guarantee the wheel hub will move nearly vertically as the wheel travels up and down, the link between the spring and lower control arm attach point stays very close to vertical, too (there is some "lean", but a bushing on each end of the bolt allows for some motion). As a result, the force through the bolt is almost purely an axial compression or tension force, depending on whether the wheel is loaded or unloaded (meaning the car is in compression or rebound).

Oh yeah, and the bolt itself is hardened.

Result: no possibility of any significant lateral forces, no possibility of sway and no chance of a snapped bolt (or nearly none).

[mgarfias]

Originally posted by RocketSled

If there was only one arm, say a Lower Control Arm, the wheel would sweep an arc shaped path as it moved up and down (this was the critical design flaw in the Corvair rear end, BTW). But because the arrangement of pivots and arms on the Corvette creates a trapezoid (rectangle) shape, the motion is constrained and the wheel rides up and down almost perfectly vertically.

Nope. You'd have that if the arms were perfectly parallel, but they're not. The tires will camber in as the suspension compresses.

The control arms also control lateral load. The distance between the center of the chassis and the center point between the left and right wheels always stays exactly the same. (this is the function often performed by a "Anti Sway Bar" in a "live axle" rear suspension. Corvettes actually have "Anti Roll Bars", which transfer vertical load, not lateral load, from one side of the car to the other to help reduce body roll in a turn). Unlike in a leaf-sprung rear end, the spring in a Corvette rear takes no lateral load whatsoever.

Nope, not at all. Leafs in the old skool solid axle cars took the lateral loads. Newer solid rears (think 3rd and forth gen fbodies) have a panhard rod that controls the axles lateral motion. Roll bars (not anti-sway bars) act as a spring controlling the relative motion of the sides of the suspension. Also, the distance between the centerline of the chassis and the wheel isn't a fixed distance, as the suspension compresses the distance decreases as the control arms effectively get shorter.

Sorry, I'm being nitpicky.

[KMeloney]

Robs -- Amazingly, I'm not sure if anyone aswered your questions. They answered SOMEONE's questions, just not many that were asked here. Hmmm...

Seriously thought... Here's my take:

The best way to really tell if your car has been lowered is to check the distance from the ground to the inside of the top of the arc of each wheel well and compare it to those of a car that hasn't been lowered. Don't ask me, 'cause I lowered mine, and don't remember the stock heights!

As for that gap, I believe it's there on non-lowered cars. That being said, that gap will INCREASE as you lower the rear, since you're essentially making that spring sag, letting the car drop down. My rear spings look as though they could snag on a matchbook they're so bowed downward...

Also, I think that based on the geometry of that set up, any movement would be up and down, and not side to side (I don't think that that bolt -- despite it being hardened -- is a weak point in the suspension.

As far as the fronts go, there's no way you're going to remove that bolt. You could remove the REAR bolts easily (that's why you hear that you should leave at least two threads above the nut), but you can't remove the fronts without taking the suspension apart. The front bolts have big, flat sections covered in rubber (bushings) that are sandwiched between the spring and control arm. You'd have to drop the suspension so much that that bolt comes out from BETWEEN those two peices -- in other words, you can't take it out unless the suspension is apart.

That being said, you want to FURTHER SANDWICH the bushings between those pieces. You want to SHRINK the gap between them by turning that bolt. Whereas you're essentially loosening the bolts in the rear to lower the car, you'll want to be drawing the front suspension pieces tighter together. Turn that front bolt so that MORE threads show above the suspension. Turn it 'til it WON'T TURN ANYMORE. (Don't know where you heard about backing off a 1/4 turn -- turn 'til it won't go anymore, and you'll know you're there.)

Ok... I just RE-READ your second question, and perhaps you weren't talking about the front at all (but that's how it reads). If you're only talking about the rears, then yes, turning that bolt TOO MUCH will remove the bolt! That's why it's advised that you keep at least two threads showing above that nut, and that you use some kind of locking nut up there. THAT being said, I just went with longer bolts in the rear, lowered it way down, and still have plenty of threads showing above the nut...

-Kirk

PS -- Hey RocketSled.... No duh! LOL (EXCELLENT post! )

[RobsZ06]

Wow, thanks to everyone...I have my answer and more !!!

[RocketSled]

Originally posted by mgarfias
Nope. You'd have that if the arms were perfectly parallel, but they're not. The tires will camber in as the suspension compresses.

Which, of course, is why I said "almost".

You would not, I am sure, argue that it *is* more vertical than if it was just a single lower control arm?

Nope, not at all. Leafs in the old skool solid axle cars took the lateral loads. Newer solid rears (think 3rd and forth gen fbodies) have a panhard rod that controls the axles lateral motion. Roll bars (not anti-sway bars) act as a spring controlling the relative motion of the sides of the suspension. Also, the distance between the centerline of the chassis and the wheel isn't a fixed distance, as the suspension compresses the distance decreases as the control arms effectively get shorter.

Hmmm. This one takes some additional thought... Panhard rods do indeed replace the "anti sway" bar of the old live-axle rearends of yore. But I could swear the more "performance oriented" applications I've had like my 94 Z28, or even as far back as my 85 SVO Mustang, had a rear axle that was supported with multi-link trailing arms. Panhard rods have something of a critical flaw that makes them undesirable in certain classes of application. Since they are fixed in length and anchored to the chassis at one end and to the axle at the other, as the axle rides up and down relative to the body, the panhard rod describes an arc (just like the wheel on a Corvette control arm) that forces the axle to move to the left and right relative to the center of the car (depending on the particular left/right mounting point configuration).

I certainly do have to agree with you on the distance comment. The distance between the centerline of the chassis and the wheel is not fixed. Geometry demands the distance must be reduced as the centerline of the wheel moves above or below the center line of the differential. The arc it describes is small, but it *is* an arc, so a cosine rule applies whenever the angle is not 0º.

However, if you re-read my original comment, you will see that I actually I say:

The distance between the center of the chassis and the center point between the left and right wheels always stays exactly the same

A grossly naive statement that assumes the left and right sides move up and down uniformly, to be sure. But for equal amounts of compression on the left and right sides, although the wheels themselves may indeed move closer to the centerline of the chassis, the *center point* between the wheels always stays in the same place.

Sorry, I'm being nitpicky.

Perhaps, but not as nitpicky as I am myself. Nyah Nyah.