Background
Many production vehicles
have mechanical stops mounted on the
suspension that limit the spindle rotation.
If a limiter wasn't provided it might be possible for the steering parts
of the suspension to contact other parts of the vehicle.
After making changes to the steering
system or suspension geometry while building or modifying your
suspension, it is
possible that some part of the wheel assembly etc might then interfere with
other parts of the suspension or chassis.
Details of why steering limiting might be required
Some (most?) rack &
pinions can move the rack shaft as far as the
teeth on the rack will allow it to move. The system depends upon
an outside device to limit the maximum amount of wheel angle in a
turn.Often when people build their own cars this limiter device is left
off or is in the wrong place for the changes made to the suspension.
I modified my steering so that two turns of the steering
wheel turned the front wheels the same amount as the old three turns
lock to lock did. The rack and pinion itself could still be turned
three turns lock to lock though. This caused my Heim rod end
mounting bolts to hit the lower control arms when the steering
wheel was turned more than one turn off center. (The bolts are
1" lower than the original hardware.)
I realize that limiting the steering the way I did it is nothing new
and has been done many times before.
But I want to present the details and the precautions that need to be
taken for other builders who might not
have seen how it's done.
What's involved in doing this change?
Basically "all" you need to do is remove the
flexible gaiter from each end of your
rack pinion, measure a few things on the rack and make up some
spacers to limit the amount of movement of the rack shaft. You then slip the spacers onto the rack shaft at each end and
put the gaiters back on.
Sounds easy enough, but you do have to
make your measurements accurate so the steering wheel turns
the same amount to the lock position left and right and check that the
suspension doesn't bind or cause the spindle etc to interfere with other parts of the car.
Why worry about having the steering wheel turn off
center the same amount?
The
reason is so that the car will have the same turning radius
turns left or right. Otherwise you may get into trouble later thinking
the car can
turn tighter in one direction when it is really the OTHER direction
that has the smaller turning radius.
Considerations and precautions
Some racks may have the bearings for
the rack shaft at the end of the rack housing. In this case the spacer
can just be centered on the rack shaft diameter and it will limit the
amount of travel of the rack shaft. I'd taper the hole ends of the
spacer so it doesn't catch on the rack teeth.
Other racks, like mine, have recessed outer bearings for the rack
shaft. i.e. the bearing is not at the very end of the housing but is
recessed a short distance inside housing. In this case the
spacer needs to be made so that it will be a light press fit INTO the
end of the housing (or the inner diameter of the spacer should be only
a slightly larger than the rack shaft diameter to center the spacer on
the shaft to clear the housing).
The reason for this is, if the spacer has a larger diameter hole than
the rack shaft and were allowed to lay on the rack shaft it could catch
on the end of the housing in a turn and change the amount of lock in
that direction. This is not safe!!
So plan on doing a little machining to get the spacer to fit
properly either on the shaft or into the housing.
Determining the size of the spacers
First thing is to support both lower control
arms so the tires just clear the ground. You need to do this so
that the wheels can be turned through their full range of movement.
Next remove the gaiters from the rack. If you have to take the tie rod
off the shaft to do this and then put the link back on hand tight once
the gaiter has been removed. The outer end of the link should also be
connected to the steering arm.
Measure the diameter of the rack shaft and write it down.
A. If you know how many turns lock to lock
you want your steering to have, do this
Center the steering wheel. Now turn the
steering wheel to one half the number of turns you want the steering
wheel to be at lock. I wanted two turns (total) lock to lock, so I
turned the wheel one turn off center. (On my setup, one turn allowed
the suspension parts to have the interference clearance I wanted so I
was OK to continue.)
Measure the distance from the bearing to the inside edge of the
mechanism that holds the tie rod to the rack.
Turn the wheel to the opposite side lock position and take the
same measurement.
Write the numbers down as they will more than likely
be different from side to side. These
measurements are the length of the two spacers you need to fabricate.
There is a picture
below that illustrates where the measurement is taken on my rack.
B. If you want use the maximum number of
turns lock to lock
do this
Center the steering wheel and then while
counting the turns of the steering wheel, rotate it in one direction
until the suspension or tire has interference with some object. Take
note of the number of turns it took to create the interference.
Re-center the steering wheel and then turn the wheel in the
other direction to see which
direction gives the minimum number of turns to contact something. Use
the minimum number of steering wheel turns as your new lock
to lock MINUS a small fraction of a steering wheel turn to allow for some
clearance between the interfering parts.
With the steering wheel at your new off center lock turns, measure
the distance from the bearing to the inside edge of the
mechanism that holds the tie rod inner end to the rack.
Now turn the wheel to the opposite side new off center lock turns and take the
same measurement. Write the numbers down as they will more than likely
be different from side to side. These measurements are the length of the two spacers that you
need to fabricate.
Limiter spacer
To see an
enlarged view of most pictures, left click on a picture or right click
and select "View Image"
This is what one of my
spacers looks like. One of
these sleeves is placed on each end of the rack shaft. The length shown
here more than likely will NOT be the same that your rack needs.
Also,
the two sleeves will probably NOT be the same length or even the same outer
diameter and that may determine how you want to make the spacers. The
bearing on the pinion
side of my rack had a tapered hole to the recessed bearing. The other
end of the rack had a straight sided tube to the recessed bearing.
I decided to make up spacers that were a press fit into both ends of the
rack rather than "floaters". I did this because I had a piece
of thick walled aluminum pipe that the outer diameter of the pipe could be
machined down to fit both ends of the rack housing and the inner hole
was much larger than the rack shaft diameter.
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