Pilot bearing? Pilot bearing???

[ejfluhr@austin.ibm.com (Fluhr)]

Here is an FYI for anyone fortunate (stupid??) enough to do their own
clutch job:  CHECK THE @#%!$ pilot bearing!

The saga started sometime in the middle of last year, when my transmission
began making intermittent noises when I pushed the clutch in.  Also,
there was an event (although I did not make the connection at the time)
where my tranny locked up and would not go into gear at all when the
engine was running and the clutch was in (I could rev-match shift, though).
I replace the clutch slave cylinder and then the master cylinder, with
no improvement.  I eventually got pissed one day and was able to jam
the thing into gear, after which time it seemed to work (although it
was sticky for a few more days).  Thinking that the clutch itself had
a problem (likely the throw-out bearing and/or pressure plate), I
installed a new clutch (disc, pressure plate, throw-out bearing, and
T/O bearing sleeve) a couple of months later.  Everything seemed to
go fairly smoothly, and the new clutch was a pleasure to use.  The noise
had gone away, so I thought everything was O.K.  I was a little confused,
though, since the old clutch looked to be in great shape, and the throw-out
bearing spun easily and smoothly.  Mistake #1:  we did NOT check the
pilot bearing (I thought it was a sleeve, rather than an actual needle
bearing, and doubted a sleeve could wear that much, so I didn't look).

The first signs of trouble showed up at Texas World Speedway, when
my brother parked the car in the pit bay after a bonzai run on the
track, and it began leaking transmission oil onto the floor.  We narrowed
it down to the primary input shaft oil seal.  I had a spare from when I
replaced the clutch, so we dropped the tranny, replaced the seal, and
had the car back together again that evening.  Unfortunately, the next
day the car showed signs of blowing oil out the seal, so the problem
was not solved.  Mistake #2:  we did NOT check the pilot bearing, AGAIN.
Several guys at the track made suggestions as to why the tranny wasn't
sealing very well;  one suggestion was that the pilot bearing could
be worn enough to allow the input shaft to wobble, allowing oil to
blow by the seal (hmmm, some forshadowing here...).

Since my tranny had also developed shifting problems (which seemed
to be most severe in 2nd, decreasing in severity in 3rd, 4th, and 5th),
I bought a used replacement tranny from an '87.5 CGT from Chris
Semple (thanks again, Chris!).  This past weekend I removed the tranny
with the help of Roger Albert (former q-lister) with the intent of
replacing the old one with the "new" one.  The new one would hopefully
improve shifting and solve the oil problem.  Well, after talking with
q-lister Gary Erickson about how his pilot bearing had self-destructed,
that bearing was one of the first items I checked when the tranny was
out.  It took us about fifteen minutes to figure out why I didn't seem
to have a pilot bearing...the bearing had self-destructed.  The only
thing left in the crank was the outer race, which at first glance seemed
to be part of the crankshaft itself.  After figuring this out, we 
noticed all sorts of little bearing pieces stuck in the nooks and 
crannies of the bell housing and clutch disc, confirming our story. 
Fortunately, Gary was kind enough to send me a new pilot bearing
(THANKS A BUNCH!!), so Roger and I spent 2 hours cutting the old bearing
race out of the crank and 5 minutes installing the new one.

I don't have the car back together, yet (got the wrong differential
oil seals from Carlsen), but I am sure that the problems will be cured.
The pilot bearing was the missing link to this mad puzzle.  The
original noise from the tranny with the clutch in was NOT the throw-out
bearing, but the pilot bearing.  When the tranny was stuck and would
not shift, the bearing had probably siezed the input shaft to the
crank shaft, imitating a dead clutch.  At speed, the input shaft
to the tranny would wobble, allowing oil to blow past the seal.  I
even think my old tranny, which shifted great before this ordeal,
still would shift nicely with a new pilot bearing.  My guess is that
at lower (2nd-gear) speeds the input shaft wobbles quite a bit and
makes shifting more difficult.  In higher gears, the higher speeds
help smooth out the wobble, improving the shifting because the syncros
do not have to work as hard.  

So, the moral of my story:


WHEN CHANGING THE CLUTCH, CHANGE THE PILOT BEARING!!!

The part only cost a couple of dollars, and will prevent you from
re-doing a clutch job (multiple times!).


Now, the really interesting question is why the pilot bearing self
destructed.  The only time the pilot bearing spins is when the 
clutch is in and the engine is turning at a different rate than
the tranny.  I am fairly easy-going on the clutch, and don't hold
it down when I am waiting at lights or anything that would cause
excessive wear on the pilot bearing.  My guess is that the prior
owner probably held the clutch in at stoplights and such, causing the
bearing to wear prematurely.  The other possibility could be the
fact that I push the clutch in to start the car, so the cold
bearing going from a dead stop to 1K rpms in a second or so may
be a contributing factor.

Now I am looking forward to getting the car back together and being
able to go whole-hog out at Texas World Speedway in October without
any reservations of the tranny self-destructing.  Should be fun.

Later,
Eric
'85 CGT, '82 urq
---
Eric J. Fluhr                                Email:  ejfluhr@austin.ibm.com
630FP Logic/Circuit Design                   Phone:  (512) 838-7589
IBM Server Group                             Austin, TX