Re: Steering box play, '87 Spider

["Paul Irvine" <kcabpilot@xxxxxxxxxxxxx>]

Dean W. Cains wrote:
------------------------------
What's the deal with steering play in an '87 Spider with the ZF box?  A few
months ago I tightened the box to remove the free-play on center.  The
other day I had to stop and move an object that was blocking my entry into
the garage, with the steering at almost full left lock.  Getting back into
the car, as I grabbed the wheel, I noticed LOTS of free-play.  Normal?  It
can't be felt during driving, presumably because both wheels are loaded by
lateral forces during cornering, and also because I rarely see full lock
when cornering.  During my last inspection a few months ago, when I
tightened the box on-center, all suspension joints were in great shape.  My
'74 Spider has the Burman box, so I thought I'd ask before comparing the
two cars.
-----------------------------

The Burman box on my Spider shattered and I replaced it with a ZF box
because I was able to get one with much less wear. Anyway, I had both of
them apart so I'm intimate with the internals until the knowledge eventually
fades away (another week or so)

They are totally different. The Burman box is helical ball bearing running
up and down a worm gear on the shaft. This moves a knuckle that is attached
to the ball bearing forward and aft. That knuckle rides in a race that is
offset from the output shaft so it rotates the shaft. There isn't any real
freeplay adjustment but there is a preload spring with a shim plate which
does seem to provide a limited method of tightening up the freeplay. The
problem with the Burman box (aside from the housing cracks and possibility
of it shattering, like mine did) is that the knuckle and race mate and wear
in the same spot all the time. This is exacerbated by the fact that they are
located at the top of the box and the gear oil that originally filled the
box and provided lubrication probably leaked out to below that level a year
after the thing rolled off the assembly line. So it's probably been working
virtually dry for the past 30 years and well let's just say that mine wasn't
a pretty sight when I took it apart.

The ZF box uses a helical gear on the shaft and this drives a sort of mating
cam that rotates the output shaft. When the cam is perpendicular to the
helical gear it is a perfect fit and there is virtually no freeplay but as
the output shaft rotates the angle of the cam to gear changes and it no
longer "fits" perfectly so the farther you get off center the more freeplay
you will have. This doesn't seem to have any effect on drivability as I
don't notice it at all while driving.

So the answer to the question is that it is normal.

Paul Irvine - Antioch CA
Project Alfa - On the road again!
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