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over thinking rear suspension. Inner strut rod heim position

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over thinking rear suspension. Inner strut rod heim position

 
Old 06-12-2019, 05:23 PM
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jim2527
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Default over thinking rear suspension. Inner strut rod heim position

Way over thinking here. Having a choice of either fully in, or fully out, does it make a difference where the inner heim is positioned in the strut bracket slots? Thinking of a trapezoid it doesn't make sense to have both the strut rod heims outside of both half shaft pivots....if that possible at all. I finally have all the parts and will be assembling my heim strut rods tomorrow. I fabricated (use that term very loosely) square washers with off center holes. I can mount the washers to either extreme by flipping.

Red dots on top are u-joints. lower left red dot is strut rod/spindle joint. Red dots are in a fixed position. Nothing can be done. But the lower inner pivot is moveable. I know the pics not to scale, its 'representative'.







Thanks-
Jim

Last edited by jim2527; 06-12-2019 at 05:35 PM.
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Old 06-13-2019, 11:47 AM
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ignatz
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What do you know about suspension geometry? Picking either A or B changes the radius of one leg of the quadrilateral that is the rear suspension. And that changes a parameter called 'camber gain'. Moving the bracket attachment point up or down, as well as changing to a different design bracket (so called 'Smart Struts' from defunct VBP) also changes that parameter.

I would suggest a good place to start with your strut rods is to match the original hole to hole dimension, with the heim joints threads at about their midpoint.

Last edited by ignatz; 06-13-2019 at 12:15 PM.
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Old 06-13-2019, 12:16 PM
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I seem to recall that the now defunct, VB&P sold their "smart struts" with an "improved" inner mount bracket. To me, it looked simply like an OE bracket turned "upside down", dropping the inner pivot point down about 3/4". This change, according to them, vastly reduced the camber change throughout the wheel travel.

One thing to remember, the C-2, C-3 IRS was designed in the late 50s, working with 6.70-15 tires....tires with about a 4", if that, tread width. In other words, camber change wasn't as critical to that narrow a tire.
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Old 06-13-2019, 04:56 PM
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Originally Posted by ignatz View Post
What do you know about suspension geometry? Picking either A or B changes the radius of one leg of the quadrilateral that is the rear suspension. And that changes a parameter called 'camber gain'. Moving the bracket attachment point up or down, as well as changing to a different design bracket (so called 'Smart Struts' from defunct VBP) also changes that parameter.

I would suggest a good place to start with your strut rods is to match the original hole to hole dimension, with the heim joints threads at about their midpoint.
Originally Posted by leadfoot4 View Post
I seem to recall that the now defunct, VB&P sold their "smart struts" with an "improved" inner mount bracket. To me, it looked simply like an OE bracket turned "upside down", dropping the inner pivot point down about 3/4". This change, according to them, vastly reduced the camber change throughout the wheel travel.

One thing to remember, the C-2, C-3 IRS was designed in the late 50s, working with 6.70-15 tires....tires with about a 4", if that, tread width. In other words, camber change wasn't as critical to that narrow a tire.

I have good understanding how the suspension works with camber gain and toe changes etc.. All original hole dimensions are correct, I didn't relocate any. Switching over to heim ends I can have the bolt at either end of the horizontal bracket slot, about a 1" difference in strut rod length. Does it matter?

I fabricated a 1/2" aluminum spacer to drop the bracket down from the diff.....a home made 'smart strut'.
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Old 06-13-2019, 06:33 PM
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Originally Posted by jim2527 View Post
Switching over to heim ends I can have the bolt at either end of the horizontal bracket slot, about a 1" difference in strut rod length. Does it matter?

I fabricated a 1/2" aluminum spacer to drop the bracket down from the diff.....a home made 'smart strut'.
I did the same thing- " aluminum spacer but I centered mine...and so did Danny Pop... Also note the center pivot is at the furthest point down...about " down...






Danny Pops set up-

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Old 06-13-2019, 08:45 PM
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Metalhead140
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I mounted mine at the outside extremity, just to keep my heims further engaged in the strut rods. I do not think there is a significant difference in camber gain, but keeping the strut rod longer (I.e. making the inner point at the innermost extremity) will increase camber gain very slightly. I just tack welded the rear washer in place to prevent it moving. I also removed the spacer that I had previously used between diff and strut rod bracket during my last round of modifications, and pictures show the outside wheel sitting better mid corner (upright or slightly negative instead of rolling into positive camber). It does feel twitchier mid corner, but as I made a number of changes at once I have not yet isolated what is causing what. But the car is significantly quicker than it was before the work. Possibly more static camber and retaining the spacer (that reduces camber gain) would provide a better result overall, but I was concerned that too much static neg camber would result in less traction off the line (and though less of a concern, will increase tyre wear also). It's all a compromise!
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Old 06-13-2019, 09:35 PM
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Originally Posted by Richard454 View Post
I did the same thing- " aluminum spacer but I centered mine...and so did Danny Pop... Also note the center pivot is at the furthest point down...about " down...






Danny Pops set up-

Note that Danny is running VBP's Smart Strut. There is no movement of the pivot location in or out, only up and down. He has it set to the extreme down position.
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Old 06-14-2019, 07:30 AM
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Originally Posted by Richard454 View Post
I centered mine...
What do you mean by this? Bolts are centered in the bracket?
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Old 06-14-2019, 02:25 PM
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Originally Posted by jim2527 View Post
What do you mean by this? Bolts are centered in the bracket?
Yep- centered in the OEM bracket- made my own "square plate washers". Struts are by "Out Pace"- greasable tube- moly ends that are staggered -so no misalignment spacer needed-



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Old 06-14-2019, 03:08 PM
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Originally Posted by Richard454 View Post
Yep- centered in the OEM bracket- made my own "square plate washers". Struts are by "Out Pace"- greasable tube- moly ends that are staggered -so no misalignment spacer needed-
Got it. Same here, staggered ends.
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