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January 22, 2014

I'm working on the carbs, but while I'm waiting for parts, I took a look at the throttle linkage.

This linkage basically turns a back and forth motion from the accelerator shaft arm to an up and down motion that rotates the carb throttle shafts.  There is also provision for spring return, a stop that limits travel, a lost-motion mechanisnm that assures a positive throttle rest position, and length adjustments for the various links.  Spring loaded ball swivels are included at various points in the linkage to give a tight, smooth action.   This all sounds great, but the assembly I took out of the car looked pretty sad.

After a little degreasing and derusting, some of the physical wear becomes visible.  The first pic shows how much the actuating rod was eaten away by wearing against the bracket (just above the bend in the upper rod).  The lower rod was a new shop built replacement, threaded and zinc plated.  The bracket didn't fare much better, with years of throttle movement sawing away at it.  The last pic shows the bracket repaired.  Although the rod is threaded 1/4-28, the original rod itself only measures about 0.218", suggesting the threads were rolled on, giving the larger diameter.  The replacement rod is a full 1/4 inch, which required the slot in the bracket to be enlarged a little.

The considerable rust left pits in some of the parts, but a fairly heavy zinc plate will protect them from any further damage.

The bell crank, which translates the motion from one rod to the other, rotates on a sholder bolt.  The fit was sloppy and floppy, and just cried out for a better bearing arrangement.  I drilled out the bell crank for a flanged Oilite bushing.  This gives a much more satisfying fit to the sholder bolt, and the flange keeps the crank from rubbing on the bracket.

The  little folded coupling clamps that grip the carb throttle shafts were just rusty, but a couple of the small bolts were siezed in their nuts and broke off when I tried to remove them.  They look like maybe 6-32, but are really 4BA threads like a lot of small fasteners on this car.

The final assembly works way smoother and tighter than how I found it, and maybe even better than original.

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