Michael Sands writes:
>...In taking appart the casting that holds the spindle, brake caliper,
>and dust shield (the name of this part escapes me for the moment)
Uhh, vertical link, in the usual parlance, I believe.
>I find a strange
>pivot joint on the bottom. This joint is what allows the spindle
>to turn as you steer the car and attaches the bottom A arm to the
>spindle. It seems to be made out of brass and is internally
>threaded. There is a grease seal between it an the threaded bolt
>like part of the spindle that screws into this brass part.
That "strange pivot joint" is the trunnion and it acts as the lower
ball joint. In fact, it isn't all that strange; *all* (or almost all)
of our LBC's have them. At least Triumphs do. The fact that it is
threaded allows the designer to have the wheel move vertically as it
is steered, countering some of the undesirable vertical movement
induced by positive castor. You will find that the left and right sides
are threaded differently (I think it has right-hand threads on the left
wheel, and left- on the right wheel, if I remember). It is brass so as
to not bind on a similarly-metalled shaft. Lubrication of the threads
is very important for the long-term life of the trunnion. On Spitfires
and GT-6's, you are supposed to lube them with 90-weight oil in the grease
fitting (which leads to the trunnion threads), but other TR's call for
grease, I think (mjb, comment?). If they go unlubed then the force of the
roadspring will strip the threads when they wear enough, and the suspension
will drop the car onto the road. You see, all of the weight of that corner
of the car is supported by those threads.
You don't say what year your S.S. is. I mention all this Spitfire stuff
because other builders, including Lotus, used those front-end parts, which
were really just stock Herald parts, and probably stamped "Alford & Alder".
Check it out carefully against a Spitfire, or maybe other builders, MG,
A-H, etc. Trunnions are available if you can be sure of the original source.
>Finally to my question, how far should the spindle be treaded into
>this fitting. Obviously if I thread it too far into the bushing
>during assembly, the spindle will bind when trying to turn the car
>to full lock (right hand turn?). Should I turn it all the way in
>and back it out a full turn, half, what?
I can look this up in my manuals if it comes to that, but I'd guess your
"Should I turn it all the way in and back it out..." is close. Turning
full lock only rotates those threads by perhaps 45 deg. (?) or so from
dead center, so you don't have to worry about a lot of rotation. More
importantly: (1) if it is threaded more, you get more thread bearing
surface; (2) the grease seal will fit poorly if it isn't reasonable snug;
(3) the amount of threading affects the vertical positioning of the wheel
on the suspension.
Someone else want to take a crack at this? I'll try to remember to look it
up tonight, but I'll probably forget...
Jim Muller
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