Trailing link orientation?

[Three Peaks]

Finally got the rear suspension pieces tacked together and the forward trailing link pivots from the Cobra Restorer's prints mounted on the chassis. Now I'm designing the pieces where the trailing links mount to the lower control arms. Since my suspension isn't exactly original, I need some input here before I weld these pieces in.

With the lower control arm level, should the trailing link mounting/pivot points be approximately level with each other- front to back? It seems that the geometry is designed that way to improve turn in on tight corners, but I'm really out on the edge of my understanding with this part of the build.

Once these pieces are welded in place, I'll have a measurement to order the trailing links with heims/rod ends from Speedway or Coleman racing. I'll be using 3/4" heims with 5/8" bores. I don't think I can make them as cheap as I can order them?
Any input would be appreciated.

I should have some pictures available in a day or two of the progress I'm making. Be gentle with me- my welding skills don't match some of the guys on this site! - Bob

[mickmate]

Hey Bob, great progress on your end. If you have it that far together just try running it through its travel. The important thing to watch for is the toe change. You will be able to clamp a straight edge to the hub to get a good feel for what it is doing. I believe the trailing link chassis mount should really be in the cockpit but we don't have enough room in there already so it finished up where it would work, sort of........
Day Motorsports also has the swaged tubes for trailing links if you want to price check them. Let us know how that works out.

[Dominik]

"The important thing to watch for is the toe change."

yes,
and "morris" did go into that extensively in his build-up at the gasholes.com forum.
get a weekend off, some beer and read...

the angle of the drag link is also cruicial, for anti-squat.

for the toe issue I got more humble opinions:
in roll
the inner wheel may toe out in roll helping corner entry, the outer wheel in. but the sum of both should not toe out!

in bump
if the outer wheel toes in in roll, that also means both toe-in in bump (out in droop)
but in bump we work together with a castor change when the wheel moves up, compensating the toe change (totally or slightly?)...
the rear upright turns clockwise looking from the side (left is front of the car)

same applies for droop, when castor changes in the other direction...

the 427s rear suspension was designed to help traction at corner entry (in roll) and at corner exit (with anti-squat, meaning more castor under acceleration).

the safer way to design your rear suspension is make everything level (as SPF did).
the position of the chassis mount for the drag link is VERY cruicial.
not the angle in the CR drawings, but the distance from chassis centerline, axle centerline and height from chassis CL.

the 427s specs from the 60s are still state of the art, used nowadays in cars like the Viper and the Lamborghini.
not the same suspension layout, but the behaviour.

comment?

dominik

[Three Peaks]

Dom,
I understand what you are saying and now that I have put the pieces together I understand how they interact. However, getting the proper geometry- especially with my bastardized 8.8 IRS rear end requires a level of understanding and a modeling program that I don't possess.

What I did in my case, was to study the CR drawings, some drawings of the original (or should I say HiTech) suspension pieces, and the way that Factory Five handled the T-bird knuckle connections. Along with input from several people who seem to have some experience in these areas, of course. Once I analyzed how that was accomplished, I tried to combine the best of those systems and tried to maintain the original geometry as closely as I could accomplish.

In addition, at all the attachment points, lower and upper control arms, and the drag links, I used 3/4" Rod ends for adjustability so I can get as much movement as possible for future refinement of the system.

For all I know, once I drive it I will find it doesn't work at all and I may have to scrap the whole thing and start over again, but at least I'm at a point where in my mind this will do what you describe above.

Hopefully, the rest of the build will be much less complicated and stressful as this particular portion has been. I took a few pictures the other day. If that would be helpful I could post them.

Bob

[Dominik]

Hi Bob,

you don't have to drive the car to find out if it behaves badly.
if you move your suspension through the whole travel and plot the camber change vs. bump/droop you get a good indication how it works.
do the same for toe and you will see.

of course, you can post pictures, but I would be hard to tell the camber change by looking a them ;-)

dominik