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

Bob Spidell bspidell at comcast.net
Tue Nov 7 13:24:17 MST 2017

The Healey hub looks a little different, with 3 'notches' where the 
synchro ring 'ears' fit, and there is an inner groove cut in all the 
teeth, presumably where the detent balls reside. Curiously, two of the 
teeth are 'sloped'--for lack of a better word--one on each side, and we 
can't figure out why.  Our best guess is that the slope relieves some of 
the pressure from the detent balls, making it a bit easier to move the 
slider in and out of gear (which, of course, would contribute to my 
problem).  I'd post a photo, but the car is at my folks' house and I 
won't get back down there until next week.

Thanks again for the help.


On 11/7/2017 11:56 AM, A H List wrote:
> Hi Bob,
> You are right, the detent won't hold the gear in if there are other
> issues such as worn or missing parts but they do sometimes drop out of
> gear on overrun or light loading just because the gear lever boot is a
> bit stiff. Later designs solved the issue by 'dovetailing' the shift
> collars which tends to pull the gear further into engagement under
> power and decel. This pic shows the very subtle machined dovetail
> where the teeth sit when engaged, maybe that is what DW has done.
> https://images.cmsnl.com/img/products/sleevesynchronizer_big23622611000-01_5351.jpg
> Andy.
> On 11/8/17, Bob Spidell <bspidell at comcast.net> wrote:
>> Thanks, Andy.
>> WRT the indents in the shift rails, I'm of the opinion that the shift
>> rails and forks should not be depended on to hold the gearbox in gear.
>> When my BJ8 started popping out of 4th, I tried holding it in gear with
>> the shift lever; the force required to do so was substantial, and it
>> occurred to me that fighting a gearbox that wanted to go out of gear
>> could result in a broken shift fork (which would have created a real
>> inconvenience when 100 miles from any town and well out of cell phone
>> range).  I plan on ordering DWR's improved 3/4 hub, which they claim
>> helps alleviate the jumping out of gear problem, along with new
>> synchros, shifting forks and layshaft.
>> Curiously, when I pulled my input and main shafts apart, I don't recall
>> the caged bearing set falling out.  I had noticed that the input shaft
>> wobbled a bit more than I thought it should; if we neglected to put
>> those bearings in at the last rebuild it's a wonder the box stayed in
>> gear at all!  Also, the tip of my input shaft had more wear than
>> expected, which could well have been from it wobbling a bit more due to
>> the missing bearings.
>> Bob

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