It's safe to say that the biggest vintage Mustang sore spot-outside of leaking cowl vents and failed window mechanisms-is unreliable clutch operation. It can be said that '65-'73 Mustang clutches are among the worst to come out of Detroit. From the factory, they had stiff pedals, erratic operation, and frustration unequalled as they began to wear. If you were hell-bent to go fast in a classic four-speed, you learned the task would never be easy.
To improve clutch engagement in old Mustangs, we opted for high-performance clutches. These made the factory clutch linkages fail, sending us to the Ford dealer for a new equalizer shaft-also called a Z-bar-which promptly broke under the strain of the high-performance clutch. To solve that problem, we welded on more steel to make them stronger. Ultimately, our performance improvements did little to fix the problem. So what can be done about chronic Mustang clutch operation?
Clutch Woe Worries & Solutions
Old three-finger Borg & Beck and long-style clutches did an excellent job of engagement for mild-mannered and high-performance engines alike. Mustang linkages were never designed to operate with these heavy-duty clutches. Old equalizer shafts, rods, and forks remain a study in bad physics and convoluted geometry, as the design doesn't work well 43 years later. Pushrods at the pedal and clutch fork wear rapidly and buckle under strain. Equalizer shafts are structurally ineffective and don't provide enough mechanical advantage or leverage against the power of a high-performance clutch. When examining the pedal support assembly, it becomes more apparent why clutch linkage failure occurs: Ford designed a woefully inadequate clutch-release system.
Under the dash, the pedal support assembly isn't up to the job, either. The pivot pin rides on plastic bushings that don't hold up under the strain. When the plastic bushings wear out, metal-to-metal contact causes severe wear.
Success comes from having good, serviceable parts. To achieve smooth operation, replace worn-out pedal supports, equalizer shafts, and other parts with new components. Service the new parts with plenty of white grease and use the felt seals provided with the kit. Make sure your clutch is properly adjusted, and periodically check it when you do a tune-up or brake job. Then enjoy the drive.
Clutch Troubleshooter
Clutch problems are easy to solve when you are armed with information. Why do clutches chatter and slip? What's that strange noise? Why does the clutch disengage only when the pedal reaches the floor? Why won't the clutch disengage? Why is there gear clash when I upshift? Here are potential problems and solutions.
Clutch performance issues are rooted mostly in wear and a bad design. When pressure plate springs grow weak through time and use, they don't hold the disc as firmly as they once did. Clutch friction discs wear out, similar to brake shoes and pads. When they become glazed, they become ineffective. Mustang clutch problems are mostly due to Ford engineers specifying a heavy-duty clutch for a light-duty linkage. Three-finger clutches create a lot of pedal pressure and are stiff because they're designed for a heavy-duty release mechanism. Not even high-performance Mustang applications had that kind of clutch-release mechanism.
The complaint we hear most is clutch chatter, which generally indicates improper adjustment. It could also come from a binding linkage. If you still have chatter once proper adjustment is accomplished, the clutch pilot bushing and transmission input-shaft bearing are the final suspects.
Here's a typical Mustang clutch linkage. The weakest link is the equalizer bar, which is a mechanical disadvantage because it doesn't provide enough leverage. Ford made minor engineering revisions to the clutch linkage during the '67-'72 model years, yet it is still insufficient. These underrated mechanisms folded over, even with stock clutches. | 
This is a look at the clutch pushrod and fork for 1965. That first year, and in early 1966, Ford located the clutch adjustment on top. This is a modified clutch linkage. | 
A closer look at the pushrod and clutch fork from the mid-'66 and up models shows the helper spring keeping the pushrod and fork in contact and in solid adjustment. As the clutch wears, the fit between the rod and clutch fork needs to be tightened. Adjustment was relocated underneath during 1966. |
A six-cylinder bellhousing tied to a Ford Top Loader three-speed manual transmission is shown here. Note the clutch release fork and bearing. The fork pivots, pressing the release bearing into clutch release fingers. | 
Here's a late-model '74-'95 Mustang bellhousing and clutch release fork. Instead of a rod pressing on the fork, this is a cable clutch set-up, pulling into the clutch release fingers. | |