Pilot bearing failure?

Discussion in '40- & 55-Series Tech' started by SteveO, Oct 21, 2006.

  1. SteveO

    SteveO

    Messages:
    306
    Location:
    Calgary AB.
    What are the symptoms of a failing/failed pilot bearing? I recently removed and re-installed the tranny/transfercase to replace the seals and when I tried to bolt them back on it didn't go smoothly. They're on and the leak is fixed but now I'm getting a funny clunking and squealing sound when the engine is under load while slowing down. Could it be the pilot bearing? Can I drive it this way or should I fix it right away? I have no idea what happens if the bearing gets worse and worse. Thanks. ....Steve
  2. Mark W

    Mark W

    Messages:
    6,171
    Location:
    The Greatland
    Very doubtful that this is caused by your pilot bearing. I have see these siezed and even seen them left out. Never seen any symptoms like you describe. In fact with the clutch engaged it really doesn't matter what condition the bearing is in, or even if it is there.


    Mark...
  3. OLDNSLO

    OLDNSLO

    Messages:
    449
    Hey steveO I am in the same boat your in. I replaced the rear output seal on a 72' with a 4 spd trans and a 3spd transfer, unfourtunately I decided not to replace the clutch, prolly should have. Now I have a rattling noice in second and third. sounds like sheet metal vibration. I have checked everything out short of removing trans/transfer again. The only thing I did not check yet is the clutch fork. The sound goes away depressing the clutch. It does not seem to affect the shifting or operation of the trans. I'll let you know what I find out.

    Brian
  4. SteveO

    SteveO

    Messages:
    306
    Location:
    Calgary AB.
    Now that I think of it, mine makes the clunking with the clutch in when you slow right down light when stopping at a light. The squealing is when the engine is braking. It kind of feels like a nut at a driveshaft flange catching the yoke a little bit or something. It's hard to describe but I can feel it as well as hear it. Any ideas? ...Steve
  5. grant5127

    grant5127

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    5,022
    Location:
    Meridian,TEXAS
    The pilot bearing is pressed into the crankshaft. It’s function is to support the forward end of the transmission input shaft, keep the clutch disc centered on the flywheel, and allow the input shaft and flywheel to rotate independently of each other when the clutch is disengaged. When a pilot bushing/bearing gets worn oversize or disintegrates, you may experience erratic clutch performance and/or shifting problems because the front of the transmission input shaft is essentially free floating. With a failed pilot, your transmission input shaft is no longer held in rigid alignment with the mainshaft and counter shaft.The gear on the input shaft transmits full engine power to the countershaft in all gears so any misalignment will cause that power to be transferred from gear to gear with inadequate tooth contact. Given time, metal fatigue will weaken the gears until a catastrophic failure occurs.Noise may also come from a worn or dry pilot bearing. Such a bearing tends to “whine” when it is out of grease. This noise usually occurs when the vehicle is stationary, with the engine running, the transmission in gear, and the clutch disengaged. Just my thoughts...
    Last edited: Oct 21, 2006
  6. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    Crankshaft......
  7. grant5127

    grant5127

    Messages:
    5,022
    Location:
    Meridian,TEXAS
    Sorry.. I was in a hurry.. :eek:
  8. SteveO

    SteveO

    Messages:
    306
    Location:
    Calgary AB.
    Thanks Grant, at least now I know what it does and it doesn't sound like my problem (yet).

    Any idea what may cause the clunking while slowing down? It happens in gear or out with the clutch in or out at very slow speeds. Feels like it's coming from the front of the tranny but I can't be sure. I can't duplicate the problem with the truck on stands. .....Steve
  9. Mark W

    Mark W

    Messages:
    6,171
    Location:
    The Greatland


    I have to disagree with you comments about catastrohic failures. I have dealt with rigs which had missing pilots bearings on three different occasions over the years. The misalignent allowed by a missing pilot bearing will case increased wear on the input bearing, and a misaligned clutch (usually causing noises and some increased wear, but no noticable performance oddities in my experience.). But the misalignment is not sufficient to cause any sort of gear failure. Increased wear of the input and it's mate on the counter shaft, to a small degree, yep. But in the real world opposed to the lab, you wil not see wear to the point that causes any sort of internal gear failure in the tranny. If you did operate the rig in this condition for long terms use, the failure would be the input bearing. Now THAT occurance could certainly cause major internal damage. But the misalingment of the input due to a missing pilot wil not cause fatigue induced failure of the gears.

    Not to say that you would want to purposely neglect to install a pilot bearing. ;)


    Mark...
  10. grant5127

    grant5127

    Messages:
    5,022
    Location:
    Meridian,TEXAS
    I just repaired a FJ25 for old timer here in the neighborhood. He neglected the problem so long that the slop took its toll on the front input shaft bearing.. the one behind the retainer. The input shaft had so much excessive play it eventually wore the scyro smooth out and would jump out of 4th. not to mention 3rd. was a bitch..The needle brgs on the inside of the input shaft are the pilot for the main shaft.. when they went south it let the main shaft drop down and those gears were running a bind.. not to mention the input shaft drives the counter shaft.. that was toast also..all in all the whole trans. ended up as junk.. but this is only one example of many I've seen over the last 40 yrs. Real common problem w/ other manufactures other than Toyota also.. for some folks this is a catastrophic rated failure adventure...
    Last edited: Oct 21, 2006

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