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Manual Drive Train and Axles Auto Service Tech Tips
These Tech Tips are provided courtesy of autoclassroom.com, an online training resource for automotive instructors, students, and technicians.
Shim it or replace it
Whenever replacing a clutch, most experts agree that the flywheel should be removed from the engine and resurfaced. When material is removed from the surface of the flywheel, the geometry (relationship) of the clutch parts changes because the pressure plate is now closer to the rear of the engine by the amount removed from the flywheel. Ask your parts supplier for a shim equal in thickness to the amount of material removed during resurfacing. Generally, these round shims are available in thicknesses of 0.020" to 0.100". The shim is installed between the crankshaft flange and the flywheel. If a shim is not used, the flywheel may have to be replaced to properly restore proper clutch operation and service life.
Use a centrifugal force pressure plate
The normal diaphragm spring pressure plate used on most vehicles today provides low clutch pedal effort for the driver. However, a diaphragm spring-type pressure plate also lacks the holding force of other types of pressure plates. One solution is to use a diaphragm pressure plate from a manufacturer that attaches weights to the diaphragm spring. As the engine speed increases, the force exerted by centrifugal force on the weights increases the holding force of the pressure plate. This additional force helps prevent the slipping of the clutch disc between the flywheel and the pressure plate.
Manual transmission service tips
A wise technician once told a beginning technician to remember these items when working with transmissions.
Always use a brass or plastic hammer when pounding on a steel or aluminum component.
If using a steel hammer, always use a brass or aluminum punch or place wood between the steel components and the hammer.
Many parts can be installed in either direction but only one way is usually correct.
If you are exerting a lot of force, you are probably doing something wrong.
Many drive train parts are pulled or pressed off and pressed or driven on.
Repair oil leaks before replacing the clutch
If engine oil or transmission lube gets onto the friction surface of the clutch, the clutch will chatter when engaged. This grabbing and releasing of the clutch is not only harmful to the drivetrain (transmission, drive shaft, etc.), but it also is disturbing to the driver when the vehicle vibrates and shakes while driving. To avoid the possibility of a chattering clutch, always repair oil leaks as soon as possible. Rocker (valve) cover gaskets, intake manifold gaskets, oil galley plugs, rear main seals, as well as the input shaft seal on the transmission/transaxle itself, can all lead to clutch contamination.
The noise test
Many service technicians try to determine which part causes noise before the clutch assembly is removed from the vehicle. Start your noise analysis by starting the engine with the manual transmission in neutral and the clutch engaged (foot off the clutch pedal). If you hear a growl or grinding sound, the cause is the input shaft bearing in the transmission. If you hear a chirping noise, slowly depress the clutch pedal. If the noise stops, the problem is lack of lubrication at the fork and pivot. If the noise gets louder as you depress the clutch, the throwout (release) bearing is the problem. The pilot bearing is the cause of a squealing noise if the sound changes as the clutch pedal is depressed or released. The sound will be loudest when the difference in speed between the engine and the input shaft are greatest. |
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