A fellow lister asked...
<< What is my best bet for the bump steer fix? I bought some aluminum
steering rack mounts, but haven't installed them yet. Seems to me they won't
cure the problem by themselves. >>
And of course the ever opinionated Nickster has to toss in his 2 cents
worth...
TVR's have used one style front end (excluding the early VW stuff) with only a
few differences up until the M chassis. The components of that system were
commonplace origins for kit cars, one-offs and race cars of the day. Some
manufacturers just got it a little better than others. TVR unfortunately
wasn't one of them. You can look at it either of 2 ways; they got the steering
rack too high, or the steering arms weren't high enough.
Anyone who has ever driven one of the pre M cars has noted the dreaded "kick
back" in the steering wheel, and the fact that ot takes 2 hands on the wheel
at all times to drive the car as it hunts and darts all over the road. Some
cars are way worse than others, but they all could have been better. (One of
my cars had a total of over 2 inches of toe out through a "normal" amount of
suspension movement...very scary ride)
OK, here's the Nickster fix. It's easy, cheap, will make your car fun to drive
again, but takes a bunch of time.
First you have to measure the amount of bump steer. There are lots of fancy
bump steer gauges around, but I'm too cheap for that. Scrounge around the
garage and find a couple of pieces of plywood and a piano hinge. One piece of
plywood has got to be at least 20" square, the other can be smaller. Use the
hinge to attach both pieces together at the edges so that you can form a
ninety degree angle with the 2 pieces. With your car on the flattest section
of your driveway, measure the static ride height. Jack up the car and remove
the bottom bolt that holds the shock/spring unit to the lower a-arm, and swing
it out of the way. Put the wheel back on and lower the car back to its static
ride height while still on the jack. Place the big piece of plywood tightly
against the tire and put something heavy on the other hinged part to keep it
from moving around. Lower the car on the jack (the tire now goes into "bump")
and measure the space between the wood and the tire.If the space is in the
front of the tire, you have toe in. If the space is in the back you have toe
out. Continue lowering the car and measuring as you go, and you can graph the
amount of toe change per change in ride height. Ideally there will be no
change in the space as you lower the car. Most TVR's I have seen will toe out
"a bunch". Toe out under bump is much harder to drive than toe in under bump,
but excesses of either are no fun.
Most cars will be found to have toe out, so I will address the fix in that
direction. If you find toe in, move everything in the opposite direction.
If you ever wanted to fix/change rack mounts, now is the time. Be sure to
remove any shims under the mounts as you want to get the rack as low as
possible. Some cars have used the Triumph steering arms, but most TVR's have
some odd longer Stanpart steering arm. Anyone know what the heck it came off
of? What you need to do to this arm is to raise the front end of it where the
tie rod attaches. Note that the very end where the tie rod hole is, is
parallel with the ground and when you are through with the mods, it still
should be parallel. Remove the steering arms and heat them cherry red between
the tie rod end hole and the first attachment hole. Using judicious leverage
(do not beat on the arms), pry the arm up in the front. Depending on the
amount of toe out, the amount that the steering arm must be bent will vary.
Try starting with about 1/2" higher, and don't forget to bend the very front
part of the arm back down so that the tie rod end hole is still approx
parallel with the ground. Let the arm air cool, do not quench it. Reassemble
the car and measure again. You may have to repeat these steps a few times to
get the bump steer as close to zero change as possible.
Do not just duplicate the amount of bend for the other side as it will not be
the same, measure both sides and deal with them individually.
Once you have the readings you want (we haven't even considered the amount of
toe change under "droop", but it is not nearly as important as the amount
under "bump") take the steering arm to your local heat treater and have them
heated and cooled to a "normal" state, then heat treated to the proper
Rockwell hardness (any heat treater should know these specs, if not lemme know
and I'll dig them out, but I can't remember the number at the moment). Do not
just put them back on the car without the heat treatment as they will be
softer than they were and could have lots of new stress points, neither of
which are good things.
Depending on the amount of bump steer, when you bolt this puppy back together
it will seem like a completely different car.
So much for another OPINION...just remember, you get what you pay for...
Nick in Nor Cal
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