Stop The Chatter Whenever...
Stop The Chatter
Whenever you have clutch chatter, check adjustment first. Also check the integrity of the clutch linkage. A binding linkage can cause chatter. After these items, look at the clutch pilot bearing and transmission input-shaft bearing. Sideplay in the input shaft will cause chatter, as will a glazed clutch disc and pressure plate. Also, any lubrication that gets on the clutch disc and pressure plate will cause slippage and chatter. Smooth engagement comes from smooth operation.
Clutch Adjustment
Proper clutch adjustment is the key to clutch survival and proper operation. As clutches wear or are replaced, they require adjustment.
Adjustment begins with what you feel and hear. With the engine running, slowly step on the clutch pedal. Take note of when you can feel the vibration of the engine's rotation through the pedal. The point between touching the pedal and feeling engine rpm is called free travel. That's the time when nothing happens, right before clutch release-bearing contact. When there is a problem with free travel, the adjustment rod needs to be changed to get it within specs.
Although Ford has an involved approach to clutch adjustment, we're more seat-of-the-pants about it. There's an easier way. Clutch adjustment boils down to feel and preference. It should never be adjusted where the release bearing-also called a throwout bearing-is constantly touching the clutch fingers or diaphragm. This will cause premature wear and failure. Turn the clutch-rod adjustment to where pedal free travel is a minimum of 7/8 inch for the '65, or 1/2 inch for model years '66-'73. You want a maximum of 1 1/8-inches of free travel. The amount you come up with depends on what's comfortable to you.
For '65 and early '66 models, clutch adjustment is at the pushrod coming through the firewall. Adjust the equalizer bar fore or aft to get 7/8- to 1 1/8-inches of free travel. With each adjustment, raise engine speed to 2,000 rpm. If you can feel the engine just touching the pedal, free travel isn't enough. That's when you must back the adjustment off to get the release bearing out of the clutch fingers/diaphragm.
Beginning in the '66 model year, Ford revised the clutch release linkage, moving adjustment to the clutch fork, where it stayed through 1973. The same situation applies here: adjust the rod tighter to reduce, or looser to increase free travel.
Once the adjustment is made, work the clutch several times with the engine running, then see how much free travel you have. Remember, the amount you have is a personal preference. Some don't like much, while others like it sloppy. Ford's limits apply in all cases.
 This is a typical three-finger...  This is a typical three-finger clutch Ford originally installed in classic Mustangs. It is a good, reliable clutch, but it's too stiff for a classic Mustang's bellcrank clutch- release linkage. |  The Centerforce dual-friction...  The Centerforce dual-friction clutch is a diaphragm/ flyweight design and is the best clutch we've ever used. Though diaphragm alone is nothing new, the flyweight/super-gripper design is. Grip increases with engine rpm. The Centerforce design eases pedal effort and releases linkage strain. |  Ford used this type of three-finger...  Ford used this type of three-finger clutch, known as long-style, in '65 six-cylinder applications. |
Quick Clutch Tech
There are three basic kinds of clutches: Borg & Beck, long, and diaphragm. We're inclined to add a fourth: Centerforce, a diaphragm-style clutch that grips better with rpm. Flyweights tied to the diaphragm increase grip with engine rpm and is a great innovation in clutch design. This is basically the only clutch we ever use.
Three-finger Borg & Beck and long-style clutches are more traditional designs. They work well, but are hard on clutch-release linkage. Although they were original equipment, they aren't the best for a classic Mustang.
Clutch Linkage Identification
When we headed to Mustangs, Etc. to learn all we could about clutch release mechanisms, we thought it would be a simple task. It wasn't. Not only was there an equalizer shaft for each type of engine, but also engineering changes from year to year. Ford struggled with warranty issues and customer criticisms regarding clutches. With each crop of complaints, the company went back to the drawing board and made changes in design.
 On the left is a 289 High...  On the left is a 289 High Performance clutch equalizer shaft, which is designed to clear Hi-Po manifolds. At the right is a standard 260/289 shaft. The difference is clear. |  Here is a '65 six-cylinder...  Here is a '65 six-cylinder shaft, which is longer than a V-8. |  Ford completely redesigned...  Ford completely redesigned the clutch release mechanism for the '71-'73 models. Instead of moving through the firewall, it runs down through the toeboard. At left is a six-cylinder, and at right is small-block V-8-actually, it's a V-8 Fairlane/Torino equalizer shaft. Mustang is similar. |
 Pushrods evolved with engineering...  Pushrods evolved with engineering changes. From left to right: '65 and early '66 with an adjustable pedal pushrod, '66 no-adjust, '67-'68 no-adjust, and '69-'70 no-adjust. |  In mid-'66, Ford moved clutch...  In mid-'66, Ford moved clutch adjustment down at the fork for ease of service. The company also eliminated the eyelet, which meant changing the clutch pedal rod to a no-adjust design. That makes '66 a modified version of the '65 equalizer shaft. When you buy a reproduction equalizer shaft for your mid-'66 and up Mustang, you must remove this eyelet. |  For '67-'70, Ford revised...  For '67-'70, Ford revised the Mustang's clutch equalizer shaft to this design. From left to right is the six-cylinder, small-block, and big-block. There's a separate part number for 289 High Performance to clear the manifolds. The big-block gets a larger shaft diameter. The six-cylinder is longer, similar to the '65-'66. The 351W and 351C for '69-'70 got unique equalizer shafts not shown here. |
 At the clutch fork, we have...  At the clutch fork, we have a variety of clutch rods. From left to right are: '65 and early '66 no-adjust, '66 adjust, '67 unthreaded block, '68 threaded block, and '69-'70 without the threaded block. |  From '65-'73, there were two...  From '65-'73, there were two basic types of clutch forks. From '65-'67, they were kept with a wire retainer, which was a frustrating design to service. Beginning in '68, Ford went to an improved slip-on pivot design (right). |  Big-block clutch forks require...  Big-block clutch forks require length and more meat. Shown here are two basic big-block clutch forks. Left is for a 390 High Performance. On the right is a 428 Cobra Jet. The 390 fork has pivot holes designed for '67 (before the Cobra Jet). The Cobra Jet fork doesn't have pivot wire holes. These forks are interchangeable with minor mods. They have identical stampings. |