Re: Panhard rod

["Tom Harais" <tjhemh@domain.elided>]

Tom:

A "straight" panhard rod is usually level when the vehicle is at rest. It
attaches to the frame on one side, the differential on the other. There
will be some lateral movement of the axle due to the 'arc' that the
differential end of the rod will travel in as the axle moves up and down,
but it should be minimal due to the length of the rod in the first place.
You'll see this set up on a lot of the new SUVs. Not the length: the longer
the bar the less change in vertical distance from mounting point to
mounting point as it travels in an arc, because the longer the bar, the
longer the radius of the arc portion of the circle it's trying to move in.

Also, there is a variant of the panhard rod called a 'Z' rod or something
like that. It is attached to the frame on both sides, but one side is
"high" and one side is "low". It attaches to the differential in the center
- literally the center of the diff cover in some cases - but the
attachement point is allowed to "rotate". There is a rod from the "higher"
bar to the "lower" bar that, in the center, is the attachment point for the
differential.

With this design the up and down movement of the differential results in NO
SIDE movement of the differential. The diff is "fixed" in place from side
to side.

I'd try ASCII art but I think I suck at it.

FRAME---------------------------------------------------------------
                                                                        -
WHEEL---------------------------------differential(         X          )
differential------------------------------------------WHEEL 
                                                                   -
                                                                 -
                                                             
----------------------------------------------------------------------------
FRAME


'X' would be the attachement point between the 'Z' bar and the
differential. it allows for the "vertical" bar to rotate. 

The attachements I've seen were "cages" set up that mounted between the
diff cover and diff using the existing bolt holes and two gaskets (one
between cage and diff, one between diff cover and cage). Think of it as a
"plate" inserted between diff cover and diff with "loops" that go back over
the outside of the diff cover with a "bolt" in the very center as the
locating and rotation point for the "vertical" portion of the "Z' bar.

Oh yeah. In order for this to work, you need the connections between the
"vertical" bar and horizontal bar at both ends to rotate as well.

Picture this, frame comes down in relation to diff. As it does, each
"horizontal" bar moves outward in an equal arc at the frame side. The
"vertical" bar rotates around it's center, allowing each "horizontal" bar
to move in this arc but keeping the diff perfectly centered between the
frame rails at all times.

Tom H.