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[chevynut]

If I had some dimensions, I'd do a drawing and settle it.

Since RD doesn't ever seem to want to be bothered with measurements, numbers, and facts, I figured I might as well measure the C4 rear dimensions myself.

The stock halfshafts are 18.125" long and the lower strut rods are 18.375" long. The distance between the two inner u-joints is 14.75" and the distance between the two inner strut rod pivots is 13.188". That makes the strut rod pivot .781" inboard of the u-joint center. The vertical distance between the strut rod inner pivot and the center of the inner u-joint is 5" (this was a LATE suspension). The vertical distance between the strut rod outer pivot and the center of the outer u-joint is 6".

All dimensions for an early suspension are the same except for the vertical height of the strut rod inner pivot.

The distance between the inner toe adjuster rod pivots is 3" (as close as I can tell) and the rods are 21" long. The inboard pivots are vertically 6.5" above the inboard strut rod pivots. I'd just assume the rods are parallel to the halfshafts, which is close. I think you have the location of the dropped toe rod inner pivots.

My rear suspension is narrowed 1.5" per side, so halfshafts are 16.625" long.

That should give you enough info to lay it out and see how camber changes from a static -.5 degrees from -3 to +3" suspension travel. The toe rods don't do anything to camber but I put the measurements here for further analysis.

[NickP]

Since RD doesn't ever seem to want to be bothered with measurements, numbers, and facts, I figured I might as well measure the C4 rear dimensions myself.

The stock halfshafts are 18.125" long and the lower strut rods are 18.375" long. The distance between the two inner u-joints is 14.75" and the distance between the two inner strut rod pivots is 13.188". That makes the strut rod pivot .781" inboard of the u-joint center. The vertical distance between the strut rod inner pivot and the center of the inner u-joint is 5" (this was a LATE suspension). The vertical distance between the strut rod outer pivot and the center of the outer u-joint is 6".

All dimensions for an early suspension are the same except for the vertical height of the strut rod inner pivot.

The distance between the inner toe adjuster rod pivots is 3" (as close as I can tell) and the rods are 21" long. The inboard pivots are vertically 6.5" above the inboard strut rod pivots. I'd just assume the rods are parallel to the halfshafts, which is close. I think you have the location of the dropped toe rod inner pivots.

My rear suspension is narrowed 1.5" per side, so halfshafts are 16.625" long.

That should give you enough info to lay it out and see how camber changes from a static -.5 degrees from -3 to +3" suspension travel. The toe rods don't do anything to camber but I put the measurements here for further analysis.

For accuracy's sake, batwing eye to eye = ? Yoke to yoke on center section=14.75? hub to hub (including hat)? Upper and lower dogbone? Distance from rear knuckle centerline to center of dogbones? I used to have a file of all of the dims but lost most of it in HardDrive crash.

[NickP]

Also, distance from centerline of inner yokes to centerline of lower strut? The 13.188 dim, isn't that the adjustable unit? Distance of knuckle center to lower strut?

[55 Rescue Dog]

Of course I wish now I would have paid more attention in geometry class, and knew CAD, but just eyeballing the stock rear, the outer toe rod joint appears to be perfectly in line with the centerline of the outer u-joint so it should follow the arc of the half shaft which is like the upper ball joint. Wouldn't moving the outer toe pivot closer the lower link magnify toe changes since it moves in and out more than the centerline of the axel? And even more so if narrowed?

[chevynut]

I did a quick layout using the dimensions I posted above for a late C4 suspension and my lower strut rod angle only changes by 0.28 degrees (steeper) with a 3" narrowed late C4 rear. It's pointing up at 3.12 degrees with the stock suspension and halfshafts level, and up at 3.40 degrees with 1.5" shorter halfshafts. The angle change moves the IC from 85.1" on the opposite side of the chassis centerline to 77.6". That moves the roll center up by a whole 0.138". Should I be worried?

Going to the early C4 camber brackets moves the roll center up more since the inboard strut rod pivot is higher. Both suspensions work great and I'm not sure which performs better. Theoretically having a roll center closer to the CG decreases the roll moment arm length, which should decrease the tendency to roll.

Haven't looked at camber yet, but I'm sure the change with a narrowed rearend is just as insignificant.

[NickP]

here is what I see. Not much movement.

[NickP]

[chevynut]

here is what I see. Not much movement.

Thanks Nick, that looks right. If I understand your numbers correctly, the upper pivot point moves inboard .062" while the lower one moves inboard .020" with 3" of compression. The lower one first moves outboard over the first 1" of compression, then moves inboard. That's a change of .042" over 6" which is a camber angle change of -.40 degrees at 3" compression.

The early suspension would actually give slightly more negative camber gain since the inner strut rod pivot is a little higher.

What numbers do you get if you shorten the halfshaft and strut rod by moving both outer pivots inboard 1.5" horizontally? Again, I think the change is minimal but I probably gained just a little more negative camber.

[NickP]

Thanks Nick, that looks right. If I understand your numbers correctly, the upper pivot point moves inboard .062" while the lower one moves inboard .020" with 3" of compression. The lower one first moves outboard over the first 1" of compression, then moves inboard. That's a change of .042" over 6" which is a camber angle change of -.40 degrees at 3" compression.

The early suspension would actually give slightly more negative camber gain since the inner strut rod pivot is a little higher.

What numbers do you get if you shorten the halfshaft and strut rod by moving both outer pivots inboard 1.5" horizontally? Again, I think the change is minimal but I probably gained just a little more negative camber.

[chevynut]

Thanks again Nick for the drawing for the narrowed suspension. However, I just noticed that you're showing a total travel of 3", 1.5" up and 1.5" down. I was looking for a total travel of 6", 3" up and 3" down in each case.