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stock mechanical clutch linkage for a 1969 Camaro or Nova.
distorted holes in an old mechanical clutch linkage
drilling holes in a large metal bracket
heim joint rod end in a clutch linkage assembly
threaded rod in a drill chuck
measuring a section of clutch linkage
cutting chromoly tubing in a vise cutter
custom clutch linkage assembly
man holding a rod end
clutch linkage bar with heim joint rod ends
side by side camaro clutch linkage comparison

Here’s the stock mechanical linkage for a 1969 Camaro or Nova. Plenty of GM cars used a similar setup. To adjust the linkage, you pull a wire retainer off the lower pushrod, remove it and turn it in or out—a big pain in the tush.

Need proof of how the 5/16 inch holes in a GM-style mechanical clutch linkage distort over time? Check out the holes in this old linkage.

The fix for distorted holes is pretty simple—drill them out to 3/8-inch using a sharp drill bit. This allows the use of 3/8-inch rod ends.

You’ll have to do the same thing to the pair of holes on the Z-bar. The bolts we’re using have a 3/8 inch inch fine thread.

Many clutch pushrod setups have a pointed or semi-ball end on the clutch fork side. To make one, cut the head off a 3/8 inch fine thread bolt and grind the end to a shape that matches the fork. I put the bolt into an electric drill motor, which allowed me to grind the piece on a stone and a piece of coarse sandpaper to get a nice radius.

I used 5/8-inch OD chromoly tubing to build the linkage. To make this work with a 3/8-inch rod end bolt, I used some thin-wall (0.058-inch) tubing and 3/8-24 to 5/8-inch x 0.058-inch wall tubing adapters. Here’s how I made the push rods. I measured the stock push rods to get the proper overall length as shown. Then I cut the tubing to length, taking into account the length of each tubing adapter, along with approximately half the threads of a rod end for each side. The tubing adapters I used measure just under 7/8-inch each when pressed into the tube. Other adapters may be slightly shorter or longer.

To cut a piece of 5/8-inch, 0.058-inch wall chromoly to size, you can use a hacksaw butted up against a hose clamp at the cut line, or use a big tubing cutter as shown here. With either method, you’ll have to deburr the inside diameter of the tubing. A fine tooth round file is perfect for the job.

The ends of the tubing for the short pushrod were filed down and a pair of Mark Williams tube adapters was pressed into place. One side has left hand threads while the other has right hand threads. Repeat the process on the longer pushrod and weld the tubing adapters in place.

I used high quality, three-piece aircraft style 3/8-inch rod ends. You can use cheaper pieces, but it’s best to stick to top brands like FK Rod Ends, QA1, and AFCO Racing, all available at Summit Racing.

Another alternative to building your own linkage is to have it made by a competent chassis shop. Here is the linkage I had Jerry Bickel Race Cars make for another project. The biggest difference between this linkage and the linkage I built is the large adjusting nut on the Bickel parts. It allows me to adjust the clutch with an open end wrench instead of having to drop the entire linkage assembly.

Here’s a direct comparison of stock linkage from a 1969 Camaro with a Jerry Bickel linkage. It’s a wonder the OEM stuff lasted as long as it did behind all the horsepower we made back in the day. It sure wouldn’t hold up behind today’s 800 to 1,000 horsepower “street” engines!

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Not that long ago, the standard clutch linkage in a Detroit-built car was a mechanical setup consisting of a fork at the bellhousing (for the release bearing) along with a couple of shafts and bell crank (Z-bar) linkage. It was simple, and it worked. But then came the 1960s. Big horsepower and torque were in, and so were big clutch pressures. Suddenly you were dealing with clutch linkages that bent, buckled, and wore out quickly.

Today’s clutch assemblies don’t need that massive leg-breaking clutch pressure, but wear is still a factor with mechanical linkage. If you look closely at the clutch linkage in a pre-1980s car, you’ll discover linkage rods that are worn at the pin ends and most (if not all) of the mounting holes in the Z-bar and the pedal are out of round.

Repairing vintage mechanical linkage is easy thanks to the wide array of replacement hardware available. But if you want a slick-acting clutch linkage that works better than the OEM setup, a better option is to build a heavy-duty linkage setup incorporating rod ends and chromoly tubing.

There are a couple of things to keep in mind as when building GM-style linkage. The mounting holes measure 5/16-inch in diameter when new, but are always distorted on old linkage. Building clutch linkage with 5/16-inch rod ends won’t help because those holes are still out of round. That means you should use rod ends the next size up— 3/8-inch diameter—and drill out the respective holes to 3/8-inch to eliminate the distortion problem.

Since the linkage is also used to adjust the clutch, make things easy on yourself and use left and right hand thread tubing adapters on each side of the respective linkage pieces. This way, all you have to do to adjust the clutch is back off the jam nuts on the rod ends and turn the linkage rod to tighten or loosen the respective link. When you use tubing adapters with all-right hand threads, you have to remove the bolts holding the rod ends in place, turn the linkage in or out, then button it back up and check the gap. If you’re wrong, you have to start all over again.

So how hard is it to build your own mechanical clutch linkage that can hold up to big power? Not as hard as you think—we’ll show you how to do it in the slide show above.

Parts List

Here are the parts from Summit Racing that I used to fabricate my heavy-duty mechanical clutch linkage:

Other Parts Required 

3/8 inch fine thread aircraft-style bolts (four required, one modified to fit clutch fork)

3/8-inch flat aircraft-style washers (six required)

3/8 inch fine aircraft lock nuts, half-inch height (three required)

5/8-inch OD chromoly tubing, to match lengths of OE linkage pushrods

Keywords
mechanical clutch
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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.