Rear suspension conventional wisdom

Hey Guys,

Whats wrong with this picture. The Chev Power rear suspension set up calls for a D height of 1.25 in. My rough measurements put the two outer link pivot points about 6.75 in. apart vertically and the two inner link pivots about 5 in apart vertically. That would mean that a D height of 1.25 would put the upper u-joint center about 0.5 in below the outer. Those we good 3D model may have more accurate numbers but my car measure like indicated with a simple scale.

The second bit of conventional wisdom is the Greenwood bit that the diff should be about 0.5 in ABOVE than the outer pivot for toe control.

Seems like the two cannot co-exist. Am I late to the party and missed the joke?

Grampy

Don't fixate on the D height, the most important thing is the halfshaft angle, you want it like Greenwood suggests, the arm has to be a little down from horizontal so that during susp. travel the arm swings close to horizontal. If it starts out at horizontal or even w/ the outer higher than that, the shaft's effective horizontal component only gets shorter during bump and this results in a toe out condition, which is bad.

Toe change first

So, toe change control is a more important parameter than rear RC height. I never did like that unintended four wheel steering.

I guess it follows that the solution is a separate toe control link combined with a trailing arm (or links) articulated on both frame and rear hub so hub yaw DOF is released and only controled by the toe control link.

Designs like C4, Pier Paulo's or TT's.

This one sounds like a big project.

Grampy

Exactly and not a 6 link like some people over yonder tell someone to do. A 6 link does NOTHING for toe control. Hell, if the factory stuff is left as it it does nothing period. A fresh diff w no stub play will give the same suspension characteristics as a 6 link, the only possible difference is either floating the stubs (bad idea IMO) and changing the geometry for an alternate camber curve, however with a floating stub there's not much room for change or the stub will move too much. The only real option then is a telescopic halfshaft.

Still leaves the real issue, the toe problem.

Twin_Turbo said:

Exactly and not a 6 link like some people over yonder tell someone to do. A 6 link does NOTHING for toe control. Hell, if the factory stuff is left as it it does nothing period. A fresh diff w no stub play will give the same suspension characteristics as a 6 link, the only possible difference is either floating the stubs (bad idea IMO) and changing the geometry for an alternate camber curve, however with a floating stub there's not much room for change or the stub will move too much. The only real option then is a telescopic halfshaft.

Still leaves the real issue, the toe problem.

Click to expand...

SO, is there ANY IRS that does not have the toe problem?? if not a 6 link...what??

12 links??:bonkers::hissyfit:

no camber change, no

I don't see the point of the commercial 6 link beyond the drag race application and a switch to a 9 inch might be a better solution if that's the goal.

As long as you have to go to a lot of work to get things under control at the back, what about a newer diff with CVs. That should take care of the half shaft problem length. Something Viperish perhaps? Any good candidates.

Grampy