To all:
I don't know that this issue has been resolved yet, believe it or else. I
HAVE come to the conclusion, as some of you have, that the correct measure
in the Bentley manual is FOOT-pounds. Although I'm no Albert Einstein in
matters mathematical, with the help of my desktop conversion calculator I
was able to nail down those metric equivalents given on page 364. {12.4 to
16.6 kgf m} is equal to {99.48 to 133.1 lbf ft.} (near as I can figure,
anyway... maybe I missed something?)
In addition, I compared those numbers with both sets of specs (metric and
standard) for the bearing pre-load {15 to 18 lbf in} and {.17 to .21 kgf m}
and came to the following conclusion:
Assuming the correct measure is FOOT pounds, in this case the nut torque is
approximately 72 times that of the bearing pre-load spec. That is, {15 lbf
in} is equivalent to {1.25 lbf ft}, and 90 divided by 1.25 equals 72. Now,
look at the metric numbers. The metric specs for nut torque SHOULD be
approximately 72 times that of the metric pre-load specs, right? So, 12.4
divided by .17 equals 72.9. Close enough for government work. As far as
the debate over what the book says, I think that settles it.
However, another list member has asked a very good question: Why is a
locking wire used on the pinion nut while nylocs are used on the side
flanges? The argument here is that nuts that do not require high torque
wrench settings, (example: front hub) typically are installed with a
locking wire or cotter pin. Why? Obviously because at the low torque
specs it is far too easy for that critical nut to loosen and cause
disaster. On the other hand, nuts spec'd for high torque do not need the
assistance of a locking wire to keep tight. At 100 foot-pounds, that nut
ain't goin' nowhere.
This issue is further complicated, perhaps, by the fact that I've not
disturbed the pinion shaft or its bearings (not that I'm aware of, anyway)
in my case since all I'm trying to do is change seals. The logic in this
matter (regarding the low-torque/high-torque lock-wire/no lock-wire issue)
seems to be pretty rock-solid, and it's buttressed by the fact that God
only knows how long I've been driving around on mine with the nut basically
finger-tight and it's presented me with exactly ZERO problems, even on a
high-mileage diff. So, I'm leaning heavily towards using a low-torque
approach, because it seems that in my case, I have much less a chance of
disturbing the critical dimensional relationships of the pinion, its
bearings, and the ring gear.
If I were finishing a complete rebuild, I might do it "by the book." But
since I'm not, I'm thinking seriously of actually following (for once in my
life, perhaps) the old addage, "If it ain't broke, don't fix it!"
Before my little diff mount repair project, the diff worked great. No
whines, and the clunking was just the cracked mount. The nut's been on
there finger tight for, well, as long as I've owned the car, (13 years) and
I've covered around 40,000 miles in it. With a locking wire in place, the
nut is not going to loosen. I don't have to tell you how ticked off I'd be
if I went ahead and torqued that baby down to 100 foot-pounds and then
discovered a nice whine or howl in the diff because I'd just MOVED
something in there by torqueing the nut down. Basically, I needed to
change the seals. But that's ALL I needed to change. Everything else
worked. So why try and mess that up?
If someone wants to try and convince me otherwise, go ahead. I'm open.
But I really am leaning very far toward leaving well enough alone on this
one, as I have no desire to suddenly find myself knee-deep in a complete
and total diff rebuild.
Pete Chadwell
1973 TR6
|