[Healeys] Gearbox jumping out of 4th gear coasting downhill or decelerating

A H List austinhealeyslist at gmail.com
Tue Nov 7 11:44:19 MST 2017

Magnus K does a neat YT vid of rebuilding the centrechange box

There is a bit of play in the needle roller between the 1st and main
shafts when the tip is not supported in the crankshaft pilot bearing.
Earlier boxes have very long individual rollers so have less play
whereas the later box has the caged bearing which is only half the
length and so appears to have more play.

One issue is that the factory did a rather average job of aligning the
indent grooves in the shift rails with where they are supposed to be
and the indent ball sits only partially in the groove so is very easy
to pop back out of gear again. The recommended mod consists of
grinding the groove slightly deeper and further forward (or backwards)
so the ball sits correctly in it when the gear is engaged.

You can check if your shift rails are ok by assembling everything and
engaging each gear with a dti gauge on the corresponding indent ball
(or a screwdriver). When the gear is engaged, the ball should drop to
the lowest position and begin to rise up slightly if the gear is
forced further into engagement. That indicates the ball is correctly
in the indent. If the ball continues to fall as the gear is forced
further into engagement, you have the same problem as I had in that
the indent is simply in the wrong position. I tried several shift
rails until I found the closest fitting ones then ground them with a
dremel to finish.

Beware of junk quality synchro rings...


On 11/6/17, Bob Spidell <bspidell at comcast.net> wrote:
> I've finally removed my geabox and done some preliminary inspection.
> Shifting forks are worn down some--not surprising in a 200K mile box--but
> all gears look to be in pristine condition.  One thing I noticed is that the
> first motion shaft seems to wobble a bit, unlike the output shaft with turns
> freely but doesn't wobble much if at all (both large bearings appear to be
> in perfect condition).  Should the rear of the first motion shaft fit snugly
> into the front of the output (main) shaft, or is a bit of play to be
> expected?   I've thought perhaps the increased compression in the new engine
> might cause some 'buckling' in the first/output shafts--more than the
> sliding hub can restrain--so could this be the cause of jumping out of 4th
> gear?
> Also, DWR sells an uprated 3-4 sliding hub, which it claims eliminates the
> 'jumping out of gear problem,' so this issue is apparently not uncommon.
> Bob
> --------------------------------
> Bob Spidell - San Jose, CA

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