What Is a Trunnion? A Fish?
By Tim Engel <tengel@isd.net>
Q: Can someone describe the idea behind the triumph based front suspension lower trunnions used on Europas? Why not just a ball joint
A: Trunnions are low-tech alternatives to ball joints. They are older than dirt and and go back to the days when machining was done on far simpler equipment. It was much easier and cheaper to bore a couple of holes in a brass casting than to precision grind matching spherical radii in a hardened steel ball and socket and stake them together.
A similar low-tech approach is the king-pin arrangement (as used on MG's). It has all the technology of a door hinge. The suspension upright is align-bored vertically (actually at a slight incline or king-pin inclination angle) and a hinge pin slipped in place. At the bottom of the pin was a steel boss that was cross drilled fore and aft to accept a bolt for the outer control arm pivot... very much like a trunnion. At the top of the king-pin, another cross-drilled boss could be bolted on, or a trunnion, or go crazy and use a ball joint.
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