Re: Spare Tire Question

[jlandry@domain.elided (John A. Landry)]

On Fri, 5 Dec 1997 07:16:20 -0800, John.Townley@domain.elided (John Townley)
wrote:

>Is there some way, without taking the covers off, to 
>determine what I have???

Again... as *I* understand things...

Not for *sure* unfortunately.  The best way is to pull the covers and
look... not only to determine if you have a locker or limited-slip, but to
see what type it is.  Then you proceed to a "peripheral" test you can do to
give you a better idea of how functional the equipment you might have is.

The easiest test that will tell you if you have a locker or limited-slip
that is *working* (not worn out or broken) is to raise one tire of the axle
being tested.  With the driveshaft free to turn (as in the transmission and
/ or transfer case in neutral), try turning the raised wheel.  *If* you
have working equipment, the raised tire will not easily turn... it will be
very hard to turn, if you can turn it at all.  If you have a true "locker",
it will *not* turn.  This is because the axle shafts will be "locked"
together and the wheel left on the ground will in effect prevent the entire
axle from turning in either direction.  With *most* limited-slip
differentials, the axle halves are supposed to be locked together to a
certain point, then when the difference in force between the two wheels is
great enough, they will "slip."  The limited-slip differential typically
accomplishes this locking and slipping through a series of clutch packs.
Having these clutch packs is why you need to use a special gear lubricant
or additive in the carrier of axles so equipped.  The clutch pack will make
noises (banging and chattering) when they grab and slip and quickly wear
out if the correct lubricants aren't used and changed regularly.

Back to the test... If the wheel in the air freely turns or has little
resistance, then you can assume you have no locker or limited-slip
differential (you have what's called an "open" carrier) or they are worn
out and / or broken.  If the wheel does turn, you will see the driveshaft
turning... this is a normal effect.  There is one exception to all of this
that I'm aware of... If you have a Dana "Power-Loc" limited-slip
differential, then the wheel in the air may in fact turn with some
resistance, but you may still have a properly functioning unit.  This is
because the Power-Loc normally operates somewhat like an open carrier
*until* there is a sufficient difference in slippage torque between the two
axle shaft halves, and *then* the clutch packs are squeezed together
through a series of cams and the differential locks-up.  Since I don't have
one, I'm not sure how it would react in the wheel spin test, but reason
tells me it could be misleading.

So what's the bottom line you ask?

If during your axle testing you feel a lot of resistance or a complete
lock-up, then you definitely don't want to put a smaller spare on that axle
and move the vehicle!  If you don't feel any resistance, then you can try
and get away with it in an emergency.  In any case (locker equipped or not)
you should probably always get the smaller spare onto the front axle.  This
is because you can leave the front hubs completely unlocked and the
differential will not come into play and isn't an issue.  The wheel will
turn totally independently of the axle shaft halves.

Hope that all made sense.

Happy holidays,

John

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