When sending in your early GM truck pressure plate for rebuilding it is important to check the center of the spring diaphragm. It is amazing how many have been damaged beyond repair.
WHAT IS THE PROBLEM?
The sealed throw-out bearing is pressed against the center of the spring diaphragm each time the driver presses down on the clutch pedal. All operates just right as per the GM design until the throw-out bearing seizes internally. Now the face of the bearing cannot spin internally. The bearing face starts turning when it is pressed against the diaphragm. NOT GOOD! This metal to metal rubbing wears down the pressure plate. It can just go so long before even breaking a few of the 18 tips on the diaphragm. It the diaphragm tips wear unevenly, the total unit is a loss.
Check your diaphragm for damage in this area when it is removed from the vehicle. The attached photos show a worn diaphragm where the shiny metal is exposed. The shine is usually not a problem if created by a good throw-out bearing. This diaphragm was never made to be rubbed by a seized bearing. We suggest you always replace the throw-out bearing during clutch replacing. The older bearing may be ready to seize and begin ruining your pressure plate!!
IMPORTANT: The opening on the ends of a used diaphragm pressure plate will always have a shine. This is caused when the stopped throw out bearing makes contact with the fast rotating pressure plate diaphragm. For a split second the bearing is rubbing the diaphragm as “total contact” is made. If the bearing never seizes, there will be little more than a shine on the opening at the hole with diaphragm. It is the cut curve in the diaphragm tip that warns of a possible totaled assembly.
Close up of the spring diaphragm
“Shine” where bearing has rubbed diaphragm
FYI: The diaphragm out of the assembly