REASONS FOR MORGAN CLASSIC DRIVETRAIN VIBRATION

This list of issues is not comprehensive. I will keep adding to it as issues or contributions allow. However, it is a good start on the process that will end your Morgan drivetrain vibration. Go to the diagnosis and checklist section first. If the issue is in the front end..check out  the FRONT END SECTION 12. And there is more remedial material within the Manual on each item mentioned here. 

1.   Motor Accesories – Disconnect the belts of all motor accessories and run motor.  Many vibrations come from fans, water pumps, etc. out of balance.

 2.   Clutch Throwout or Release Bearing - When you install the (new) throwout bearing, remember that the fork AND the springs go INSIDE THE GROOVE in the bearing - I see them installed wrong all the time, with the curled ends of the spring capturing the flange on the back end of the bearing - result is inability to get correct clutch adjustment/free play. 

Install the flywheel (always have it resurfaced before this procedure), clutch disc, pressure plate and clutch housing on the engine. Be advised that there can be NO oil or grease on your hands, the flywheel or pressure plate friction surfaces, or on the clutch disc. If there is, the clutch will grab (chatter) when being engaged. Install the correct length clutch fork on a 1½" long pivot that has the correct head type for the retainer on the fork (refer to fork and pivot information previously discussed). Position the fork so it sticks out of the clutch housing at about 4 or 5 degrees less than a right angle with the engine centerline (this would be when looking down on the engine from above—the fork should be ahead of, or less than a 90 degree angle by 4 or 5 degrees). 

3.  Motor Mounts - Morgan motor mounts are a wear part. The rubber interface dries, cracks, deteriorates over time and must be replaced. Additionally, bolts to other parts in the mount assembly, or to the frame or motor will loosen and fall out.

 

4.   The Pinion Angle - This is tthe angle the pointy input shaft to the transmission makes with its contact with the engine drive shaft. As a general rule, the pinion angle shouldn't be set relative to the ground, or exact level, but rather to the output shaft of the transmission.  The important thing is that the two center lines are parallel., 

5. The Drive Shaft U-Joints

While it is possible to run at zero degrees through the U-joints, something more than actual zero and less than three degrees seems to run smoothest. Angle induced vibration will be high frequency, twice engine RPM in direct drive. It may show up only on acceleration or deceleration. Adjust the pinion down to correct acceleration and up to correct deceleration vibrations, plus or minus one degree is usually enough. Before adjusting anything, make sure the U-bolts holding the driveshaft to the pinion yoke are not overtightened. Correct torque is 17 foot pounds and no more.

6.  Driveshaft (Prop Shaft) Phasing

To check your U-joints, jack up your car and support it on jack stands. (Never crawl under a car supported only by a jack.) A visual check will tell you if your U-joints are lined up correctly. Simply compare each end of the driveshaft to see if the yokes on each end (the parts welded to the driveshaft tube itself) lie in the same plane. (In a Morgan you may have to open the gear box cover access panel). If they do not line up, or are at right angles to each other, it is usually a simple matter to unbolt the propshaft and re-orient the splines of the two pieces to bring the universal joints into proper phasing.

7. Driveshaft (Prop Shaft) Balance

If your shaft is not balanced with the actual end yoke and U-joints, you have not fixed the potential vibration problems. A driveshaft will not run smooth and vibration-free unless it is straight and in balance. The recommendation is to have shaft dynamically high speed balanced at 10,000 rpm by a driveshaft professional. Typically, if the shaft is out of balance it will start to vibrate (and make a droning sound) somewhere around 50-60 mph and then get worse as speed increases to a point, and then get somewhat better at even higher speed...much like the vibration effect with a problematic Morgan front end.

If making a new driveshaft correctly, measuring is done by putting the yoke in until it bottoms out and pull it back 3/4 of an inch. Measure the length of the U Joint centerlines and have a shaft made with that length. If the yoke is too short to accomodate this correctly you will have a stange vibration so check your drive shaft for proper fit. Put the car on a drive on rack or on jack stands. With the car's weight on the suspension as you would drive it, disconnect the shaft from the pinion yoke. Push the drive shaft forward until it bottoms into the transmission. You should be able to drop the rear u-joint cleanly past the pinion yoke without resorting to a tool of any kind. Any clearance up to 3/8 inch is  fine. 

8. An Engine Anomally 

Lean misfire or bad/fouled plug.  A very common cause of vibrations is a misfiring cylinder. A cracked spark plug insulator, smashed gap or broken ground strap, are some of the causes. If you suspect a misfiring cylinder, the best was to isolate it is to pull each spark plug wire one by one, at idle, and note if/when there is a resulting rpm drop. Ten browse the GoMoG Manual for help. 

The pilot bushing is seldom thought of as a part of the clutch system but it is one of the most vital parts of the system. It holds and pilots the end of the transmission input gear into the crankshaft. It holds the input gear steady as its "nose" twirls inside the bushing. If it is worn or not running "true", it can cause serious clutch problems or transmission failure. Pilot bushing bore runout should always be checked with a dial indicator and should be within .002 total. The bronze bushing type should be a press fit into the crankshaft bore. It must be installed carefully. It should have between .001 and .003 clearance on the transmission shaft when installed.

So the job of the pilot bushing is to support the end of the input (main drive) gear in the crankshaft. It only acts as a bushing when the clutch is depressed. This pilot bushing should be a light drive fit into the crank bore. Care should be taken when installing any pilot bushing as they are soft and easily damaged. A damaged pilot bushing can bind on the input gear giving symptoms of clutch drag. Transmission damage and early failure can be caused by a pilot bushing or crankshaft bore that "runs out" in relation to the transmission locating bore in the bellhousing. A slight scratch on the bushing will cause a mild noise when the clutch is not enaged. This is annoying but not harmful. Plus 8s are infamous for this.

It is advisable to check the bore of the crank with a dial indicator before installing the pilot bushing (see below). If the bore runs out more than .003 total, the crank should be set up in a lathe and the bore trued up OR a special pilot bushing should be made that runs out the same amount as the crank bore.

To check alignment, use a dial indicator with the base mounted to the crank flange to check the transmission pilot hole for concentricity to the crankshaft center line with +/- .010”.  Check the face of the bellhousing (where the transmission bolts up) for squareness to the back of the block.  Variance should be no more than +/- .010” side-to-side and top to bottom. Also check the fit of the transmission to the bellhousing and the fit of the pilot bushing to the transmission input shaft.

9. Flywheel Runout   

Check the face of the flywheel for runout with a dial indicator. Runout should not exceed .005". If it does, the flywheel should be resurfaced. If runout exists after resurfacing, the fault is either in the resurfacing job or there are burrs, dirt, or dings on the crankshaft or flywheel hub. Remember there is end play in the crankshaft bearings and this must be held in one direction when checking flywheel runout (or bellhousing face runout).

To check a bellhousing, mount it on the engine it's going to be used with, make sure there are no burrs or dirt on the block or bellhousing. All bellhousing to block bolts should be in and tight. Mount the dial indicator on the crankshaft of the engine using a suitable magnetic base attachment or mechanical clamping means. The contact point of the indicator should be touching the bore of the bellhousing. The indicator must be mounted rigidly enough so it does not move on its mounting to prevent false readings. Rotate the engine by hand with the spark plugs removed and observe the reading on the dial. The total number of thousandths misalignment of the bore relative to the crankshaft is read directly on the dial. Total runout should not exceed .007", with .010" being maximum. The greater the misalignment, the sooner transmission problems and failure will occur. A symptom of misalignment is unusual wear of the pilot bushing. We have checked stock Chevy bellhousings on engines that were out more than 1/32" (.032"). Some Ford one are reportedly worse. Anything over .010" runout must be corrected before the engine and bellhousing are put in service or you can count on pilot bushing, transmission, and clutch problems, followed by transmission failure. The simplest way to correct misalignment is to try another bellhousing or bellhousings. Machining the bellhousing is the best cure but offset dowel pins are simpler. Shims between the block and bellhousing will also work if you have the patience to use this method. Offset dowel pins are sometimes available from "speed shops."

Vehicle Drive Train Vibration Diagnosis Checklist