Quote:
Originally Posted by GOLDCYLON
From the ZF.Doc
I replayed the video about twenty times. It sounds like the pilot bushing is
compromised. Install GM fluted pilot bushing (GM P/N 10125896). WARNING: Applying grease in an oil-lite type pilot bushing will cause the pilot bushing to fail within the first one percent of its normal life expectancy. Although very dry looking straight out of the bag, the oil-lite type pilot bushing is infused with enough oil to lubricated the input shaft pilot tip for the entire service life of the clutch. Why not just install a pilot roller bearing instead? When a pilot roller bearing fails, the input shaft pilot tip will be compromised requiring removal of the input shaft for pilot tip repair or replacement of the input shaft.
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I install pilot roller bearings with grease and assume they will last a very long time without wear or bearing failure which failures are very rare for the Pilot Roller Bearings.
Some additional information from ZFdoc from previous discussions.......commenting on the correct diagnosis by Marc Haibeck of Pilot Bearing Noise.......
"Marc Haibeck is correct, it is a faulty pilot bushing for sure judging by your description which was very good by the way. To fix this problem, the exhaust, driveshaft, driveline support beam, transmission, bell housing and clutch assembly will have to be removed in order to remove and reinstall a new pilot bushing.
What causes a pilot bushing to fail?
Grease applied to the inside diameter surface of an oil-lite (oil saturated) pilot bushing is the number one cause for pilot bushing failure. Grease applied in a pilot bushing eventually dries up and clogs the otherwise normally self-oiling pours of the bushing. When installed clean and dry, a pilot bushing should typically provide up to one million release cycles of service whereas when grease is applied, the bushing service life is drastically reduced down to approximately 5000 cycles or less. Typical time to failure with a grease contaminated pilot bushings is around 1.5 years from time of contamination.
The purpose of the pilot bushing is to provide centering support of the input shaft at the far end for maintaining optimal clutch disc to friction surface alignment. With loss of pilot support integrity at the far end of the input shaft comes accelerated wear of the clutch disc friction surface at the outermost region of the disc.
GM has a revised design of the pilot bushing called a fluted pilot bushing (GM P/N 10125896) which has six narrow grooves formed on the inside diameter surface of the bushing which act as scrubbers to prevent glaze from forming on the input shaft pilot tip leading to pilot failure. GM also makes a pilot needle roller bearing of which many people prefer over using an oil saturated brass bushing. The reason I prefer bushing over roller bearing type pilot is because when a bushing fails it usually does not compromise the input shaft pilot tip surface.
In the rare event of a pilot roller bearing type failure, the input shaft pilot tip surface is typically compromised requiring disassembly of the transmission in order to replace the input shaft or to have a machine shop install a new pilot tip surface on the input shaft doubling or tripling the repair cost over just replacing a compromised pilot bushing."