[Healeys] OD Longevity

Bob Spidell bspidell at comcast.net
Sun May 15 11:04:56 MDT 2016


I've always been a bit in awe of the Laycock De Normanville overdrive 
units as fitted to our Austin-Healeys.   To me, it's a wonder of 
engineering elegance and simplicity--well, except for the electricals, 
maybe--and as it's an 'axial' design there are no significant side loads 
to wear out layshafts/gears and bearings. However, all things have a 
life span and I'm wondering what is the typical life for the A-Series--I 
believe that's what's in my BN2 and BJ8--OD units under 'normal' 
(non-racing) usage?  The unit in my BJ8 has over 190K miles on it and 
AFAIK it has never been overhauled, and I'd hate for it to die on one of 
my long road trips as we inevitably spend hours on straight stretches of 
interstate highways (I do have a 3.54 rearend, which would make things a 
bit more tolerable, but the 22% reduction in RPMs is hard to beat; 
except maybe with 28%).  I've used Redline MT-90 in the gearbox/OD for 
the last 40-50K miles or so and--some will think this is blasphemy--I 
only change it out every 20-30K miles (I don't buy into the 'use 
non-detergent oil so the all the sludge will drop to the bottom' theory, 
when I change out the syn oil I note the oil is clean and light-colored, 
and that there is finely-ground brass shake suspended in the oil but it 
is so fine you can't feel any grittiness at all if you rub it between 
your fingers; and note that some of the best greases--lithium, 
molybdenum, etc.--are finely ground soft metals suspended in oil).

Anyway, what's the collective wisdom on this: run 'em until they quit, 
or rebuild them at 100/200/300/?K miles as a precaution?

As usual, TIA.


ps.  I'll keep using 74W-90 in the diff as recommended by y'all.

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