Diff Question...

[treed2 at wsu.edu (T. Reed)]

Jason,

There are two kinds of 020 diffs, the older (open) 2H type and the newer
"mini-slip" 4K/AGB type. Let me explain..

For some reason or another (I have a hard time believing it was for
traction purposes) the factory began (somewhere between '83 and '84) using
a new diff that included brass shim rings on each side of the diff.

You see, you can take a normal diff and spin both wheels the same
direction, nothing amazing happens. Now spin just one wheel.. the other
wheel will spin the opposite direction. The shim rings provide some
friction between the two wheels so that if you spin just one wheel, the
other wheel spins the SAME direction.

(as an aside: all this is necessary because when you make a turn, the
outer wheel is spinning faster than the inner wheel)

The older diffs do not have these shims, and the same is true for many of
the newer ones because the shims tend to break (and wear out) very easily!
You will frequently take off an inner CV flange and discover little brass
bitlets floating around. This doesn't really hurt anything to not have
these shims, it just makes you lose your "mini-slip" feature.

I have a 4K and when I took it apart and put it back together again I
considered replacing them but the cost something like $17 each so I said
"screw that" and re-used the old ones. When I had it all back together I
found that spinning one flange caused the other to spin in the same
direction, as it should. But I could easily overpower this effect by
twisting one flange in the opposite direction with what I
(generously) gauged to be about 5 to 10 ft-lbs of torque. I don't think
that the mini-slip does much; that's my opinion.

To answer your questions now-

When you say your tranny is in gear I assume you mean the tranny input
shaft is not moving and is held steady, right?

And you're probably turning only one of the output flanges and seeing that
it just spins. This is normal. The other flange has less "traction" (so to
speak) so it is "getting the power" (or steadiness, in this case) while
the one with the most traction (the one you are exerting force on) is
slipping. This is normal behavior for an open diff.

(Yeah, its stupid.. that's why a torsen diff is such a great thing: the
wheel that grips gets the power, rather than the wheel that slips - but
thats sort of a simplificiation)

The little bit of effort you might need to get that one flange to
freewheel is the effort to overcome the shims mentioned earlier. If its
almost no effort at all then there's a good chance your shims are broken
or missing, or you have an early diff.

The diff will not really die unless some part inside your tranny breaks
off and gets stuck between the gear teeth (this most frequently happens to
the r&p), the output shaft splines strip out (I've never heard of this),
or you somehow manage to shear the teeth off the spider gears or
something. Oh, and SMS or a severe blunt impact to the case that causes it
to split.

If you're getting a slipping sensation while driving, your clutch is
probably hosed. It sounds to me like your diff is perfectly healthy.

HTH,

-Toby

On Mon, 1 Dec 2003, Jason Rinne wrote:

> Sooooo, when your tranny is in gear, the diff is supposed to lock to a
> certain amount of pressure right? You shouldn't be able to just freewheel it
> with liitle effort, right? If the diff is hosed on my tranny, what are my
> options? Would this cause a "slip" similar to a worn clutch?
>
> Thanks!
> Jason Rinne
> Bellingham, WA
>