Listers,
You may remember the saga of my BJ8 jumping out of 4th gear after an
engine rebuild.? While sorting out the issues in the gearbox and OD I've
been pondering why the car would start doing this after an engine
rebuild when it hadn't done it for over 100K miles before.? Thanks to
people on the List and the Forum, I've noted some possible culprits:
1) weak detent springs on the shifting forks
2) weak or worn springs or balls in the shifting hubs
3) excessive end play
4) other/all of the above
I don't think it's the shifting forks' job to hold a gear, but it's been
noted that especially stiff shift lever boots could command an unwanted
shift, but I don't think that' the issue as my shifting forks, springs,
etc. are in fairly good shape, and I could feel the shifter fight to
release from gear when I held it.? #2 is very likely a contributor (I'm
replacing mine as the small gears that mesh with the synchro are worn).?
#3 is certainly a possible cause, as Dave P and others have pointed out,
but I think it's a combination of things, and one that just dawned on
me.? A poster--I believe it was Steve Gerow--has been alerting owners to
a problem caused by too thick paper gaskets on the rear axle hubs.?
There's a spacer in there, whose job it is to clamp the outer race on
the bearing to keep it from turning, but the new gaskets are too thick
and prevent the axle disk from clamping down on the spacer sufficiently
to apply the necessary pressure to the spacer, and spun bearings can
ensue (I heard of a shop doing a pretty steady business fixing rear axle
hubs with spun bearings).
Similarly, there are thin shims at both the front and rear of the
gearbox that are there to apply pressure to the gearbox front and rear
bearings.? Magnus K notes in his (excellent) video that these are
critical to minimize end float in the input and main shafts, which can
cause the jumping out of gear.?? When I split the adapter from my OD I
noted that the original--AFAIK--gasket was very thin; paper thin to be
exact (unfortunately, I split the bellhousing and gearbox and didn't
save the gasket, which was installed at the last rebuild about 130K
miles ago).? The new gaskets that Moss, and probably others, provide are
much thicker than this.? The front shims for the gearbox are either
0.002" or 0.004", and the rear are 'A/R' and none are available (at
least from Moss).?? A random gasket I pulled from the set--which, I
believe, are also for some MG and/or TR cars--measured 0.019", a lot
more than the width of available spacers.
Obviously, I can't prove any one cause conclusively, but if the shims
are for a setup with, say, a 0.002" gasket, then a 0.019" gasket is
going to eliminate the pressure that should be applied to the bearing
outer races.? This also fits with the behavior of the box, which had
jumped out of gear a few times after a previous engine rebuild, but had
settled in and not jumped for over 100K miles.? And now, the problem is,
where do I get an 'original style' gasket, which is probably only a thou
or two thick?? It is not practical to 'roll your own' as these are
complex gaskets and there are many openings that need to line up.? Note
these are smooth, machined, non-porous surfaces which should not require
a thick gasket to fill imperfections like, say, a thermostat housing
(yet the gaskets appear to be made out of the same thick material).? I
could use a silicone or other sealant, but I am more comfortable with a
gasket with a bit of sealant spread on it ('belt and suspenders' as it
were).
Anyone else seen this problem?? Oh, and I've got 2 gaskets sets minus
the front and top gaskets for a centre shift gearbox available to a good
home for postage.
Bob
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