Re: Bump Steer, Steering Components, Hemi-Joints

["Steven Stegmann" <steve.stegmann@xxxxxxxxxxxxx>]

MessageJeff,

I believe I came in on this thread late.  Please fully describe the symptoms
for me again.

A classic case of bump steer in a Scout has the vehicle steering right when
the right wheel moves above its rest position with respect to the body and
left when the right wheel moves below its rest position with respect to the
body.  This is if the right end of your drag link is lower in elevation than
the left end of the drag link when the vehicle is at rest.  The behavior will
be reversed if the right end of the drag link is higher than the left end when
the vehicle is at rest.

Worst I've ever driven is a stock Chebby Citation (or clone).  Going south on
I-25 on the south side of Denver back in the earlly 80s there was a dip where
the southbound lanes circled to the west around some obstacle.  As the lane
moved back east there was a big dip, many vehicles long so you only noticed it
going fast.  That Chebby would suddenly move half a lane.  It would give you a
laundry kill during rush hour.  I think that may have been the best feature of
the Citation.

Steve
  ----- Original Message -----
  From: Jeff Bade
  To: 'Steven Stegmann' ; 'IHC Digest'
  Sent: Thursday, July 03, 2003 9:12 AM
  Subject: RE: Bump Steer, Steering Components, Hemi-Joints


  Since this is stock hight at the moment.. (even though my lifted scout which
has everything else stock is nowhere near like this)

  Should I be looking for worn components then?  Mismatched or out of balance
tires?
    -----Original Message-----
    From: Steven Stegmann [mailto:steve.stegmann@domain.elided]
    Sent: Wednesday, July 02, 2003 10:12 PM
    To: Jeff Bade; IHdigest
    Subject: Re: Bump Steer, Steering Components, Hemi-Joints


    Jeff,

    Your use of Heim joints has nothing to do with bump steer.  On something
like a Scout there is usually only one source.  The two ends of the drag link
are not at the same elevation.  What happens is that as the wheel end of the
drag link moves up & down with suspension motion, the wheel end describes and
arc in a vertical plane.  If the drag link is level, the left & right
component of the drag link motion is minimized.  The further the link is from
level the greater the component of the motion becomes left & right.  That's
why as the axle moves up the vehicle steers one way and steers the opposite
direction when the axle moves down.

    Contrary to popular belief the shape of the drag link has no bearing on
the situation.  It is only the relative elevation of the two ends of the drag
link that matters.  The best fix is to get a pitman arm which makes the two
ends of the drag link the same elevation.