I had received several requests from listers who were interested in the Rack
and Pinion Steering conversion I did on TS36967E. Sorry for the length, it
is a tough topic to address in 50 words or less...
A steering conversion kit is offered in the UK by (I believe) a Co.
called Pro-Tech. The fellow who handles these in the US is:
British Auto Restorations
4002 Brandon Ave. SW
Roanoke, VA 24018
Attn: Mr. Ted Smith 540 989
5121 No Website yet
The rack is from a Mini-Cooper (S?) and is fitted with the appropriate tie
rod assemblies.
They supply some steering shaft conversion bits, couple of universals and a
shaft segment as a solution for the split shaft vehicles. I do not have any
info on the long steering shaft solution.( but is available...) The vendor
supplies some robust mounting brackets that use the original steering box
and idler arm mounting positions on the frame. No irreversible hacking...
I had installed 2 previous rack units in my car, a GT6 and an MGB that were
not to my satisfaction. ( bad bump steer, wrong turns ratio...) The TR3 is
a very narrow car, and most donor car racks are set up for wider tracks.
When you install the wider rack, you end up with short little tie rod
assemblies. As the suspension travels up and down, these little tie rod
assy's do not travel in the same arc-path as the suspension components.
When the suspension moves up and down, the toe in/ toe out condition changes
significantly, which leads to really bad handling. SO, the key is to design
the steering so that the tie rod assemblies are reasonably close in length
to the upper and lower control arms, so that as the suspension travels up
and down, no significant change in toe in/toe-out occurs. In addition, you
must also consider what happens when the car is driven around in a
reasonably tight circle. The outer wheel travels a larger radius path than
the inner wheel. This requires a ' Toe-out" condition, which is also
known an "Ackerman" ( whoever he was....) This effect is designed into the
steering by careful positioning, front to back, of the steering rack. ( the
position is set by the brackets supplied...) If you were to draw an
imaginary line between the centers of the outer tie rod joints, positioning
the rack slightly behind this centerline will provide a degree of
'Ackerman'. Too far forward will result in a toe-in condition during
cornering, which is really bad!! one wheel fights the other, instead of
taking the car around the turn.
After the installation of the Mini Cooper rack, I still had some
bump-steer. Subsequent head scratching made me conclude the brackets, as
supplied by British Resto, locate the rack about 3/4 of an inch too low,
which gives rise to the following problem- Picture in your mind (for you
Mensa types!)/ sketch on paper what the front suspension looks like when
viewed from the front of the car. The upper and lower control arms are
pointing slightly downward, i.e. the inside bushing position is a bit higher
than the outside lower bushing position. The upper and lower control arms
are approximately parallel, I measured them at somewhere around 6 degrees
from horizontal. When I measured the tie rod assemblies, they were now
headed 'uphill' by a couple of degrees, in opposition to the control arm
orientation. Now think about what happens when the car hits a bump and the
suspension moves- The outer tie rod end travels an arc which starts from a
position which is higher than the inside tie rod end. It will therefore tend
to pull the steering 'lever' arm towards a 'toe-in' condition. Conversely,
the upper and lower control arms , pointing downward by about 6 degrees,
cause the wheel spindle assembly to travel outwards, as it travels in
response to the bump. This movement, which occurs naturally in all 'control
arm' systems like this, actually worsens the toe-in condition. The spindle
assembly is headed towards a wider track, and the steering lever is being
pulled inward, and the wheel is then directed to a further toe-in
condition. I did some rough calculations, and sure enough, the toe in
changes by about 1/8" on a 2" suspension deflection. This doesn't sound
like too much, but it did seem noticeable on the road. I made some 3/4"
spacers to raise the rack mounting position, which made the control arms
and the tied rod assemblies travel in the same arc-paths. The car now
drives very nicely, the steering effort is light and responsive, the turns
ratio is suitably quick, and there are no compromises in turning circle or
tire scrub...
Other issues:
You do lose the fan and hub extension, the kit includes an electric fan (
I already had installed one) and thermo switch. Obviously the turn signals
become an issue, as the center mounted control head and horn button have
nowhere to go now. I had previously installed a GT6?Spit? upper steering
column and stalk mounted directionals and Hi beam switch, so I didn't have
to fiddle around with the original stuff this time around. .... It is a
project, but certainly not an insurmountable task. The guy who runs British
Resto- Ted Smith- seemed very helpful and quite honest. He claimed to have
done about 20 cars so far...( NFI)
Sorry for the long winded blather. I've been trying improve the
steering on these cars for a very long time, and this time I am definitely
satisfied with the result.
Regards,
Bob Westerdale
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