Originally Posted by rtillery34
This is the second pilot bearing im having to put in, in the last 6 months. What causes them to fail? Bad bearing? Install incorrectly? Bent input shaft? Any ideas or suggestions to check while I have the tranny out would be greatly appreciated! Thanks!!!
A shaft needs to bearings to run true, which is why you have a pilot (it is the second point of support, with the input bearing being the main.)
Potential causes of pilot bushing/bearing failure?
- Failed/failing input bearing
- Bent input shaft
- Defect on input shaft pilot (especially if you have a bushing)
- Defective input bearing, allowing excessive shaft play (axial or radial)
- Insufficient lubrication (even though most pilot bushings are "Impregnite" - oil-impregnated sintered bronze - some grease on assembly usually does not go amiss. Just a touch - enough to augment the oil impregnated into the bushing. Use a bit more if you have a roller bearing. In either case, moly grease is preferred - since the lubricant doesn't get renewed, you need every advantage you can get. Use moly, unless you do a lot of water crossing -then go with a good lithium soap grease (like used on trailer bearings.)
Typical specs for input shaft movement are:
- Endplay (axial) - 0.003" or less
- Endplay (radial) - 0.002" or less
- Runout (indicates bent shaft) - 0.002" or less.
Endplay is measured by simply wiggling or pulling on the shaft, measuring runout requires turning the shaft. All may be measured quite accurately with a common dial indicator (run the sensor tip on the pilot surface, fix the base so it doesn't move and give you a "false high.")
Check the pilot surface visually for defects before measuring - if you see
something, use your thumbnail on it. If you can feel
it, it needs to be cleaned up (stoned flat) or the input shaft replaced. I do not know if a "sleeve" kit is available, but any machinist should be able to make something like that for you on a lathe. Turn the pilot down to size, turn a bushing to fit with the proper OD and an ID with a 0.0010"-0.0015" interference fit - heat to install (about 500*F should do - drop it on and let it cool.)