Steve,

By Traclink, are you referring to the Global West Unit? The traclink is definitely a shorter arm than a stock or LG and the assembly bolts to the floor panels. It looks less rigid than many TAs out there. Is this what you use?

http://www.globalwest.net/camaro93.htm#TRACLINK%20kits

Bolt on Traction for STREET, DRAG or ROAD RACE " TRACLINK kits"
(fits 1982-2002)

Benefits and Features:
Attaches to the rear axle and controls rear end torque during acceleration, transferring this energy into the tires, increasing straight line traction.
Reduces nose-dive during braking.
Eliminates wheelhop.
Increases sidebite for corner exit acceleration.
Simple bolt-on system does not require complete interior removal as with other kits.
Provides an attachment point for driveshaft safety loop.
Removes the factory torque arm pivot point from the rear of the transmission.
Changes the instantaneous center and leverage point from stock.
Provides adjustable pinion angle.
Note: Traclink kits are designed for V-8 applications.

 

Fore and aft movement of the torque doesn't change pinion angle. It doesn't change the angle of the torque arm because the whole arm slides together which is connected to the pumpkin and it slides with it, there's no rotation.



Fore and aft movment of the torque arm does not doesnt change pinion angle because it doesnt exist. The only movement fore and aft is whatever the rear LCA bushings delfect. However the arms moving for and aft in its front mount is because the change in pinion angle. When the axle rotates up or down the arm will move in its mount. Simple really.

 

How did you break it? Did you do anything you haven't done before? Yes, it does bind and this will fatigue things over time.

He's wrong (unless you have no rear brakes). It certainly doesn't "float." The front of the arm does put a downward force on its mount during braking. However, it won't be as large as a hard launch. It isn't dependent upon the acceleration of the vehicle, it is dependent upon axle torque. During a launch, all the acceleration is comming from axle torque. During braking only 25% or so of the work is being done by the rear brakes so the load is much smaller. If you start axle hopping, however, those loads can be much higher than a launch (assuming you aren't running a 10 second car that pulls the front wheels).

No, even without bushing deflection the LCA's don't move straight up and down at the axle. They scribe an arc. That arc will move the axle fore and aft. This movement is required for the suspension to move freely and is why you need a TA that can change length.

With a rigid torque arm, the axle won't rotate up or down. The only time axle rotation can cause fore/aft movement of the torque arm is if the torque arm flexes--a ton.

 

Time to break out the SVIC figure? Seems to me that axle rotation that's a function of vertical suspension motion can't help but involve fore/aft plunge of the TA. Except in the specific (and unlikely) case where in side view the chassis LCA pivots and the TA front mount coincide (both vertically and longitudinally).

Norm

 

Norm, axle rotation is a function of engine torque. It is a direct cause of it. The torque arm's function to prevent the pumpkin from rotating, and let it transmit as much power to the wheels without losing traction.

A good rigid torque arm will prevent axle rotation, while the lower control arms allow travel needed for proper suspension geometry.
And of course the panhard locates and centers the axle.

Have you ever tried to break a really tight or seized bolt with a long ratchet, that is made of cheap steel? Have you ever seen the beam of the that ratchet bend in an arc and prevent you from breaking that bolt?

Then you borrowed your friend's heavy duty forged professional ratchet and tried to break the bolt again, this time it didn't flex
and the bolt broke free.

Think of the resistance of the bolt (which is preset torque) as the engine torque transmitted to the rear end, and the ratchet as the torque arm.

You see why a rigid strong torque arm is so important...

 

EXACTLY


Regardless of what causes axle wind up it happens. Regardless of the TA. Which is why good arms have a provision for fore/aft movement.

I dont buy the LCA causing the movement. Almost all movement of the LCA's is one at a time. One moves the other does not (or at least very little) This will cause the axle to twist but not move fore or aft.

The arc swung by the LCA will cause very little movement when BOTH wheels hit the same bump.

Again the stock F body handles so well that making improvments can be kept very simple. That is why ESP cars are faster than almost if not all SM cars. Mods that work, work better than all the mods.

Have fun all!

 

>Regardless of what causes axle wind up it happens. Regardless of the TA. Which is why good arms have a provision for fore/aft movement.

Fore and aft movement of the torque arm does happen, and it happens significantly during acceleration and braking. Why? Because weight transfer causes the rear of the body to squat during accel and lift during decel.
When either happens, the lca's will move (in an arc) at different angles relative to their mounting points on the frame. This angle change causes the effective lca length to be longer and shorter. This is what moves the axle fore/aft, and as a result, moves the torque arm in/out.

This also happens when the car turns, it's called axle steer, where lca's change in their effective length.


>I dont buy the LCA causing the movement. Almost all movement of the LCA's is one at a time. One moves the other does not (or at least very little) This will cause the axle to twist but not move fore or aft.

Not necessarily, if you were to accelerate on a flat surface both lcas will try to resist lifting the axle, and plant it down. But because the body is shifting down (squat) it changes their effective length.

>The arc swung by the LCA will cause very little movement when BOTH wheels hit the same bump.

Again, depending on the bump, and how soft the suspension in the rear is, it's hard to tell how much the torque arm will move fore/aft. The most extreme cases are during accel/decel and hard turns...

ESP cars are limited in mods compared to SM, but I believe that you are allowed to change the torque arm in that class.

 

OK. You're looking at it from the straight-line perspective at the drivetrain generated deflections and rotations (deflections in reaction to traction, actually). But you're absolutely correct that rigidity is required here. A limp-noodle of a TA would be little better at controlling pinion angle than the monoleaf springs on some 60's cars with Hotchkiss suspension.

My point of view is from that of suspension behavior, hence my previous explanation in those terms. This is probably picky, but whenever you accelerate (and have less than 100% anti-squat) you'll get squat, and with that you'll still get TA plunge, and the suspension-caused pinion angle changes will add algebraically to those permitted by TA flexibility.

Norm

 

 

>When a swing arm increases in length the movent also increases. Have you measured the amount the rear axle move when put through it's paces? Its not much. And if the rod ends are good the movement in measured in thousandths. And a PHR is what about 4 times as long as a LCA? So the lower control arm causing fore/aft movement is not true. Pinion angle changes causing movent is pretty easy to picture.

What swing arm? Are you referring to the torque arm or lca?

The only arm on the car that can change real length is the torque arm, because is moves in/out of its member. This is assuming the stock torque arm/random tech/ lg/ traclink.

Define putting through it's paces? Go out to your car and brake from 120mph-0... what does the car do? It dives forward, does the rear end stay the same length from the tunnel as it did when the car was at rest? No it stays glued to the ground, until it reaches full suspension droop.

Pinion angle will only change if the torque arm flexes, otherwise it will stay fixed. This effective pinion angle is measured by subtracting driveshaft angle by the pinion angle (angle finder on the base of the pumpkin). So when the driveshaft changes angle, so does the pumpkin because the arm holds both together fixed.

The control arms connect the axle to the frame, if what you were saying was true, then how could the control arms let the axle move the torque arm in/out of its mounting, keeping in mind that you said that control arm movement has nothing to do with the fore/aft movement of the arm?

 

I'm sorry guys. My statements above were so poorly written--to the point of being technically wrong--it seems I've just created more confusion. My bad.

When I said the only time you will get axle rotation, I was thinking of the comment on pinion angle change. What I meant was axle rotation in relation to the driveshaft. With a torque arm roughly the same length of the driveshaft (as the stock is) you won't get any amount of pinion angle change (pinion angle defined as angle between the driveshaft and pinion only--this is not how it is always defined) unless the TA bends no matter how the suspension is moving.

But as the axle moves up and down relative the the front mount of the TA, it obviously changes angle a bit and requires the TA to change length--it's just that the driveshaft changes angle by the same amount, thus no pinion angle change. Something else I left out--with a shorter torque arm they don't change exactly the same amount so there is some pinion angle change with vertical movement of the axle. But it's very small.

Beyond that, I want to reinforce that the arc scribed by the LCA's is the reason you need the TA to change length. Their change in horizontal length isn't much, but if they're rod ended and a TA has a fixed rod end front you have virtually zero slop in the system. That little bit will cause a bunch of bind.

Also, don't forget that if the LCA's are parallel with the ground statically, during body roll one points down, one points up so the both shorten in horizontal length pushing the axle forward, plunging the TA in its mount.

Does that make more sense?

 

We have already agreed that the arc scribed by the LCA will in essense shorten or lengthen the arms. And according to you cause the axle to move in and out. Again it is a TINY amount.
The swing arm I am speakg of is not an arm but the PHR. The longer the arm the larger the arc. So this says that because the PHR is so long that when suspension compresses the axle is put out of center by alot.

But it is not alot it is very little. And you better checek the Trac linc again. About the only fore/aft movement it has is the busing deflection.

 

The swing arm in these cases is a virtual swing arm rather than a physical one. One end is at the axle shaft centerline (we're looking in side view). The horizontal location of the forward end is somewhere along a vertical line that passes through the TA chassis mount. The vertical location is where a line passed through the LCA pivots intersects that vertical line. Granted, this "swing arm" is kind of imaginary (hence the "virtual" part), but it does describe the motion of the axle relative to the chassis.

Quote:

But it is not alot it is very little. And you better checek the Trac linc again. About the only fore/aft movement it has is the busing deflection.

The magnitudes of these movements may be tiny, but they cannot be ignored when the discussion involves forces and moments induced by compressing/distorting the bushings. Such forces/moments interfere with predictable suspension behavior. Traction arms (torque arm-like devices that are pinned at the chassis end like the GNX piece and Kirban's copy of same, and apparently the Trac-link) that wouldn't move at all but for bushing compression may work OK at the strip, but they don't belong on anything for which good cornering behavior anywhere near the limit has importance.

Norm

 

The Traclink does have a sliding mount, which is fixated on the main beam, between the ends of the mount are two rubber bushings. As the the arm moves in/out it will pull/push on these bushings during extreme weight transfer/cornering.

Some people end up trimming these bushings to eliminate a thunk sound during acceleration.

As far as proper fore/aft movement is concerned, the traclink fulfills this requirement, and is not considered a fixed pinned
arm design.

Steve

 

It does? Must have been an old version that you had. I am 99 1/2 % sure that the one Mike had did not have a slider at all. It attaches to the main beam with the two bushings as the only provision for fore/aft movement. Just like all the others I have seen.

Norm I agree that you cant ignore the fact that a very slight difference on each side of the car will produce undesireable results. And I speak of LCA movement causing axle steer. Simply proving a point that the arm is not moving due to LCA movement.

And while I do not like the Trac Linc, and have heard of Concrete evidence of torn sheet metal, I would not say that it is no good for what we do. The car just has to have a few things done differently.

It has won at least 2 national championships. Would have been 3 if not for the inclusion of the M3 in ESP. For one year.


Back to the original point is that the mount of the Spohn will not creat any bad side effects due to the front mount. And if not for wanting a little shorter arm I would think the LG arm would be very good. Just would like to see an adjustable unit.

If not for class restrictions I would go with a long arm. Like a Random Tech. Also note that the ESP national champ car this year had a random tech. And of course he has recomended it to me but I would like to take my chances.