Have questions about C4 Corvette suspensions for your Tri5? Ask them here!

[chevynut]

RE the UCA transverse angle, drivers side to passengers side, is just a matter of curiosity. It would be a nice reference.

Still not sure what you want here . Are you asking for the angle of the upper a-arm from the balljoint to the k-member? Where do you want it measured, and at what ride height? I would just set the lower a-arm where it needs to be, and wherever the upper one sits is where it sits.

Back to the LCA transverse angle, I'm still finding contradictions on this angle. I need some assistance and guidance here so I can move on...
I read that this LCA angle, measured from the pivot point of the lower ball joint to the pivot point of the inner LCA pivot is "0" degrees. This make more sense to me and visually looks very simular to my C4 Vert..

It's not easy to visualize where the center of the lower balljoint is.

The "Z"measurement procedure puts the bottom of the front suspension cross member, what seems to be too high !! With my car rack tied up I have no means to check my C4's engine cradle high nor the LCA. It would be a nice reference, but prob not reliable. So, how do I set the correct ride height, exactly.

Is that z measurement stuff from GM? If it is, it seems like it should be reliable but it does seem high. Note that it's also for an EARLY C4 since the tires are listed as 255-50VR16. They went to 17" wheels in 88.

Also, why would "Z" increase from shipping weight to curb weight? Curb weight is with full tank of gas, and shipping weight is half a tank. Why would they ship with gas? It doesn't make sense that "Z" would increase at curb weight. Notice it DECREASES in the rear and it's essentially the same measurement.

I just measured my frame jig and I get only 19mm for the "Z" measurement if I'm interpreting it correctly. When I put a level on the top of the lower a-arm where it's shown as level in the drawing (just to the right of the pivot), I measure the a-arm being level and I'm pretty sure the steering arms are level there too. I had some measurements for the UCL and LCL pivot points on the other thread, as well as UCL/LCL lengths and spindle heights.

It seems to me that a line between the LCA pivot and the lower balljoint should be level at ride height. The suspension should work up and down around that. I would just set the ride height where you think it should be . If that's a 46mm for the "Z" dimension, then set it there. If you want the a-arm level, set it there...that's where I set it. You can always adjust it from there if you want to....as long as you align it at that new height.

[oceangoer]

Yes, I see this suspension drawing is more than likely for the early C4. Is it correct, no idea but I don't trust this drawing.

Agreed, this measurement seems too high.

Yes, The Z measurement changing "shipping to curb weight" is a mystery. Which points to someones home made drawing possibility.

One the snow clears off again, I'll have a few extra pairs on hands and we'll determine the RC "Roll Center" !! I want to keep it high and close to my CG, which is an estimation.

Here's a quote.... There's always a trade off ! But I have a good idea where the RC should be, now I'll check it out the olk fashion way with strings to find out how close.. I would be satisfied knowing that i'm in the mid-range. Most all of the referances show the Roll Center bove the road surface and slightly under the LCA pivot..



Effects of Front Roll Center Adjustment

Front roll center has most effect on on-throttle steering during mid-corner and corner exit.

LOWER front roll center

* More on-throttle steering
* Car is less responsive
* Better on smooth, high grip tracks with long fast corners


HIGHER front roll center

* Less on-throttle steering
* Car is more responsive
* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)

////////////////

Effects of Rear Roll Center Adjustment

Rear roll center affects on- and off-throttle situations in all cornering stages (entry, mid, exit)

LOWER rear roll center

* More on-throttle grip
* Less grip under braking
* Use to avoid traction rolling at corner entry (increases rear grip)
* Use under low traction conditions
* Increases traction, reduces rear tire wearHIGHER rear roll center
* Less on-throttle steering
* Car is more responsive
* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)

[chevynut]

With a level lower a-arm, the roll center will ALWAYS be above ground. To raise the roll center the lower a-arm has to point up at the inboard end. Maybe that's the reason for the 46mm "Z" specification in the drawing.

Note that with the late lower rear strut rod brackets, the roll center was lowered and rear camber gain was decreased. The "D" measurement on a late rear should be considerably less.

[oceangoer]

Laz,

Yes, I understand. I'm very close right now. But until We get the frame table set up and AME finishes my frame rails, we're on Project Hold....

I'm only shooting for getting close to the 3.30 RC in the front. I just spoke with Don @ Flat Out and He concurs. Don always marks every front C4 suspension member with the C/L for the axle, I'm as close as I can with this front sus assembly situated on blocks, but it's sitting slickly over 1 degree up on the LCA.. We'll check closer when the frame rails are squared up..

It's also nice to know that the '57 LCA set up height and "0" is correct !! Hope to get that engine cradle tacked in this weekend, maybe welded up.. Soon off the frame table, I need is soon.....

Yes, I've read that info on the rear RC. Goes to show what happens when a design is pushed too fast - one of many changes.

Thanks again.

Michael...

[oceangoer]

Anyone have the dimension from the rear axle C/L to the face of the u-joint Yoke ??

[NickP]

Anyone have the dimension from the rear axle C/L to the face of the u-joint Yoke ??

See #71 in this thread - 14.75"/2

[oceangoer]

I have that dimension. That's the center of the Pinion.

I need the dimension to the face of the face of the U-joint yoke or flange, going forward..

Thanks though

[NickP]

[chevynut]

I have that dimension. That's the center of the Pinion.

The pinion is not in the center of the differential case, it's offset, and the amount of offset depends on whether it's a Dana 36 or Dana 44.

[oceangoer]

NCW,,

YES, that's it