Linkage Lessons

You know you’re a hard-core Bow Tie enthusiast when you start thinking about ways to make obscure parts such as clutch linkages work better. Since performance car building is what we do, we’re always looking for improvements. Virtually all Chevy musclecars used mechanical clutch linkages up until the early ’80s. Like most enthusiasts, we’ve had our share of problems with clutch linkages, so we set out to improve upon Chevy’s production design.

The factory Chevrolet system was designed to accommodate a light-duty, diaphragm-style clutch even when used behind stout power big-blocks. The system uses a bellcrank that decreases effort through leverage. This lever ratio is determined by the combination of the pedal leverage and the length of the arms on the bellcrank, often called a Z-bar. While the system works well, the connections between the pedal, rods, and bellcrank all create friction and are subject to wear. After 100,000 miles, these friction points elongate the holes and wear out the pins, creating a sloppy linkage that will fail at the most inopportune moment.

The easiest thing to do is just replace the worn linkage pieces with new ones. Resto houses such as Classic Industries, Original Parts Group, Ausley’s Chevelle Parts, and several others offer complete linkage kits or individual replacement parts for restoring your car’s clutch linkage system to like-new. But we figured we could improve upon the stock system. The best way is to eliminate the friction points is by using spherical bearings or rod ends. These rod ends not only eliminate wear but also greatly reduce sloppiness and make for extremely smooth linkage operation.

The system we upgraded was designed around an early Chevelle, but the concept is exactly the same for a Camaro, Nova, or Impala. All these linkage rods use pins that fit through holes in the Z-bar and the clutch pedal. These pins measure 5/16-inch, so we used a series of 5/16-inch male spherical bearings to replace these pins. We also substituted 5/8-inch chrome-moly steel tubing (0.049- to 0.058-inch wall thickness) for the solid rods. We found everything we needed to create these new pieces in the Art Morrison catalog. The only other parts we needed were some fine-thread 5/16-inch bolts and nylon plastic locking nuts to prevent the whole mess from coming apart.

Morrison also offers threaded tubing adapters where one end slips into the tubing while the other offers either left- or right-handed threads to accept the male spherical rod end. We ordered enough 5/16-inch right-handed, commercial grade 5/16-inch male rod ends, and right-handed threaded tubing adapters to build a couple sets of linkages for our two four-speed Chevelles. Then we went to work.

There are two rods used in the GM clutch linkage: one from the clutch pedal to the Z-bar, and one from the Z-bar to the throw-out bearing release arm. We measured both of these rods and cut the tubing to length, accommodating both the rod ends and the tubing adapters. The rod ends feature a relatively long male-threaded end, so the length of these rods are adjustable plus or minus 2 inches. To begin with, we adjusted the new spherical rods to duplicate the factory clutch rod lengths.

Once the tubing was cut and preassembled to check for the proper length, we simply plugged in our 110-volt Daytona Mig to weld the tubing adapters to the steel tubing. The rod ends were then installed and the lock nuts tightened to prevent the tubing adapters from moving. Since changing the length of these rods is not something we’ll do very often, we used two righthand tubing adapters and rod ends to make ordering simpler. However, if you wanted to build similar linkage pieces for other uses such as throttle linkage, engine limiters, or engine pulley adjusters, fitting one end with a lefthand thread and the other with righthand thread allows adjustment to the length without disconnecting the rod. March Pulleys offers an adjuster like this for its alternator mount that is very trick. Now you know how to build your own for a custom application.

Once the rods were assembled, we bolted the new rods to the clutch pedal and Z-bar with fine-thread 5/16-inch bolts. Since we don’t want these fasteners to come loose, we used nylon-locking nuts that have a nylon insert in them to prevent them from loosening. As an extra preventative measure, we also applied a small dab of blue Loctite to the threads. If you’re really paranoid, you can also drill the end of the bolt and run a cotter pin through it to prevent the nut from coming loose. However, we’ve flogged this linkage for well over two years on a daily-driven El Camino and never had a problem with the nylon nuts loosening. However, if you remove them several times, always replace the nuts with new ones since they will loosen if they’re re-used often.

On our Chevelle, the rod from the clutch pedal to the Z-bar requires a slight bend to line up with the Z-bar that we did not apply to our custom tubing link. Spherical bearings can handle a certain amount of misalignment without binding, and we were still able to bolt everything together without a problem. Ideally, if you have access to a tubing bender, you could duplicate the bend in the factory rod to compensate for the misalignment.

For an afternoon’s worth of work, we created a trick spherical bearing clutch linkage that works well and will live for as long as you drive the car. The best part is when a hot rodder asks you where you got that trick clutch linkage. You can honestly tell them, “Oh, I just whipped that up in my garage.” That alone makes the effort worthwhile.