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Unread 10-18-2013, 02:42 PM   #1
rtillery34
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What can cause the pilot bearing to go out?

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!!!

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Unread 10-18-2013, 02:44 PM   #2
Apollo12227
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Contamination inside the bearing. Dirt or sand in the bearing at install.

Some people install the pilot bearing using a socket that fits the edge of the bearing race. This can sometimes be an issue if they pount on the socket too hard, deforming the edge of the bearing causing it to run hot and fail early.
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Unread 10-18-2013, 02:46 PM   #3
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When the Co-pilot gives him the wrong frequency!!!
Ha, I keel me!!!

Seriously though, If you can switch to a bushing, you will see more miles. A bearing is will work fine, however one bad tap on the install and it is bad from the get go. Which may be your problem. If the original failed and the replacement was installed incorrectly, you may just have had bad luck. In my opinion, I would run a bushing! And check the input shaft bearing in the transmission.
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Unread 10-18-2013, 05:05 PM   #4
rtillery34
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Thanks guys for the input! I thought as well it my have been during the install too. I checked the input shaft for looseness when I had it out the first time and the shaft bearing seemed fine but then again a 26yr old tranny may be ready for some new parts!
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Unread 10-19-2013, 01:43 AM   #5
Opihi59
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Perhaps put in in backwards, like I did here? http://www.jeepforum.com/forum/f12/p...lation-513450/

I've pounded in a ton of pilot bearings in my lifetime, but it wasn't until I put up that thread that I discovered there is a thin side and a thick side to the pilot bearing. Install the with "numbers out" and it likely will be fine. This one I drove in the opposite way and found that the rollers were binding since I damaged the race. Something to think about.
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Unread 10-19-2013, 02:15 AM   #6
5-90
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Quote:
Originally Posted by rtillery34 View Post
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.)
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