Don,
This is an ancient line of discussion on the net, but I'm jumping in with a
minor update in my experience.
OK, waaaay back in 1968 when my first B-GT w/OD was fresh out of the
box (and so was I)the conventional wisdom was non-detergent 30W,
non-detergent so that particles would not remain in suspension but
precipitate out of the oil and stay out of the OD plumbing. I used
this. Eventually I tried 5-50W aviation oil, but the OD would not
stay engaged and I went back to 30W. Everything was OK. When that car
(and I) T-boned a Pontiac in '78 the tranny still performed perfectly.
Fast forward to 4 years ago when I got my second B-GT w/OD, a '72.
When I got it the oil in the box seemed to be 90W, stiff shifting and
a jarring OD engagement. I first went to 30W, as in past practice.
There was a nasty whirling noise in third gear, and some in 4th.
Someone in this forum said "Redline is great for trannies," so I
invested in that. Sound was the same, but OD would not easily engage.
Local LBC shop recommends 40W to quiet the noise and for OD. Noise
drops a bit, OD works, engaging is a bit sharp, but not too nasty.
Meanwhile, the overwhelming majority of opinion in this forum is "same
oil as the engine," or, as John Twist recommends, 20-50W. Last year
my OD stopped working fulltime. It turned out to be a loosely
connected wire at the transmission cutout switch, but before I found
that, I did a number of other things, including replacing seals in the
OD and switching to 20-50W. Now it works great--that wire is back
where it belongs--and the shifts into OD are much smoother. AND, for
some inexplicable reason, the third and 4th gear noise in my tranny
has pretty much disappeared. In this, as in Lucas electrics,
apparently only God knows why.
Jay Donoghue
72 MGB-GT
66 Mustang
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