Clutch problems spoil my fun

Question:

I have a 1969 Mercury Cougar XR7 convertible with a 351 Windsor and an Edelbrock 4-barrel carburetor (it originally had a 2-barrel carburetor). The car came with a 3-speed manual transmission but now has a 4-speed. I was experiencing a bit of clutch chatter.

Reviewing the receipts that came with the car showed the clutch had been changed about nine years ago. There was no mileage information. I purchased a stock clutch and pressure plate (RAM 88769), ARP pressure plate and flywheel bolts and a new pilot bearing. During installation I had the transmission mount and the universal joints replaced. Unfortunately, I still have the chatter.

My mechanic says it may need to wear in but that has not happened. Besides the chatter in first gear it is still difficult to get a smooth shift into second gear, as it tends to grab. I love driving a standard shift car but the clutch problems are taking the fun away.

Answer:

If oil is leaking from the rear main seal, intake manifold or elsewhere at the rear of the engine it can find its way onto the clutch disk, where it would cause the disk to chatter. But I assume you would have noticed oil on the old clutch and surrounding areas when the new clutch was being installed.

Absent oil on the disk, chatter with a new clutch, pressure plate and flywheel is normally due to an imbalanced pressure plate and flywheel assembly, a defect in the pressure plate that causes uneven clamping force to be applied to the clutch, or something wrong with one or more of the other parts that impact the performance of the clutch.

Were your pressure plate and flywheel balanced together and then assembled in the correct orientation to maintain the balance? I learned the hard way that it is never a good idea to install a new clutch without having the flywheel and pressure plate precisely balanced by a qualified machinist. The machinist will mark the pressure plate and flywheel with a scribe, small punch or something similar so that you can install them in the correct orientation in order to maintain the balance.

While it’s certainly reasonable to expect a new clutch, pressure plate and flywheel to be in proper working order they aren’t always—another lesson I long ago learned the hard way.

I always recommend against buying rebuilt clutches or pressure plates because in my experience they are far more likely to perform poorly. And I never install a new flywheel without checking to make sure its friction surface is true and flat.

After the flywheel is installed you should also check its run-out to make sure it’s not more than a couple of thousandths of an inch at the very most at its outer perimeter. If the flywheel is straight but has excessive run-out when installed then the crankshaft is bent or the flywheel mounding flange on the crank has an irregularity or is not perpendicular to the crank’s centerline.

Another area that you should carefully check is everything that impacts clutch position and alignment. For the clutch disk to function well it must remain parallel to the flywheel and pressure plate. Since the clutch disk rides on the transmission’s input shaft the shaft needs to be precisely perpendicular to and centered to the flywheel and pressure plate. Measure the transmission input shaft to determine if it’s straight and perpendicular to the main case mounting ears. Look for burrs or other defects on the shaft’s splines and make sure the clutch slides back and forth easily on the input shaft.

Also check the bell housing alignment with a dial indicator to make sure that the opening in the bell housing that the transmission inserts into is precisely aligned with the centerline of the crankshaft, and that the surface the transmission bolts to is perpendicular to the crank’s centerline. Sloppiness from wear, bent or otherwise damaged components, or incorrect parts in the clutch linkage can cause the clutch to engage and disengage unevenly, causing chatter. Replace any parts that are evidently worn or damaged. Also look at the pilot bushing and replace it if you see any signs of wear.

My final bit of advice concerns the installation. Use a good quality alignment tool to align the clutch before tightening the flywheel. Do not use the transmission’s mount bolts to force the transmission to move into position. If the clutch is aligned well the transmission should fit snugly but not so snugly that you have to force it into place. Do not use an impact wrench or air ratchet to install the flywheel or pressure plate bolts. Follow the manufacturer’s torque specifications and tighten all bolts in a staggered pattern.