In the last issue, we took a look at why a heavy-duty, “bomb proof” mechanical clutch linkage is important, even with today’s low pedal pressure clutch assemblies. If you recall, many original linkage systems out there are already past their best-before dates, with "ovalled" holes and other issues. A rod-end based large tube linkage will resolve the wear issue forever. But that’s not the end of it: A high quality custom fabbed linkage will provide you with all sorts of adjustment capability. Sound interesting? Check out the following as we complete the build:
Cars like ‘50 5-6-7 Chevys and many early Corvettes used a roll pin on the clutch fork end. But many other cars with mechanical linkage make use of a pointed or semi-ball end at the clutch fork side (for example, a first gen Camaro). A return spring pulls the works tight, but you’ll still have to fabricate a ball end to seat in the fork.
Grind the Bolt
Here’s how you make it: Cut the head off a 3/8-inch fine thread bolt (common right hand thread) and it grind to a shape that matches the fork. No lathe? Chuck the bolt into an electric drill motor. That allows you to “turn” the piece on both a stone and a piece of coarse sand paper to get a nice radius. When done, chase the threads with a 3/8-inch fine thread die.
In this photo, you can see how the modified bolt fits into the clutch fork.
We used these high quality Aurora three-piece (“aircraft”) 3/8-inch rod ends on the other ends of the linkage – one for the lower and two for the upper. The uppers are left and right hand thread; the lower is a left hand thread. As pointed out earlier, the use of left and right hand threads makes for easy adjustment.
See the nut welded on the pushrod? It’s a piece Jerry Bickel Race Cars offers. You simply slide it over the 5/8-inch tubing and weld it in place. It becomes the adjuster nut.
Turning the Linkage
Because of the left and right hand threads on each tubing adapter, the nut allows you to turn the linkage “in” or “out” after backing off the jam nuts on the rod ends. Obviously, this setup is a whole bunch easier than dropping the linkage to adjust the clutch.
Here’s a look at the stock upper linkage for a first gen Camaro (or Chevelle, or Nova, or…). Plenty of cars use a similar setup.
Compare it to the custom lower linkage in the second photo. It’s easy to see why these OEM pieces bent and buckled way back when big pressure clutches were in vogue.
Check out the completed lower linkage (at the top) in the photo. The spindly piece (at the bottom) is the stock linkage. To adjust the stock linkage, you pull a wire retainer off the lower, remove it and turn it in or out. With the custom setup, you back off the jam nuts and simply turn the big nut on the link.
This is what the linkage looks like assembled in the Z-bar and clutch pedal. It’s easy to adjust and you can build it.