Re: Questions on AWD, ABS, and locking the rear differential

[LToy@aol.com]

Frank Deutschman writes:

>Actually, all diffs (open and limited slip) allow different rates of
rotation
>on the two output shafts -- that is the purpose of the diff.  AWD does not
>depend on a limited slip -- in fact, most Quattros throught the years were
>not equipped with a limited slip on either the front or rear axle; most
Quattros
>were/are equipped with open diffs front and rear.

Not counting race/competition cars, were ANY quattros equipped with LSD?  

[explanation of open/limited/Torsen diffs deleted]
>The Audi Quattro system uses a Torsen between the front and rear axles to 
>optimally split the torque front/rear.  

Only the most recent models (the 80/90/100/200 monikers in the US, post
'88-89) came with Torsen center diffs.  Prior to that, the center diff was an
open, usually lockable diff.  
[snip]

>>  Some 4-wheel drive trucks 
>> have the wheel lock mechanism on the center hub of the wheel.  
>
>On a 4WD, the hub lock mechanism is *not* a diff lock.  (Most 4WD's are
>equipped with ordinary open diffs on both ends, sometimes with limited slips
on
>the rear, but never on the front, at least from the factory.)  The hub lock
>mechanism actually is used to disconnect the front wheels completely 
>from the front diff (the wheels freewheel, regardless of what the diff is
doing).  

Right--not a diff lock.  Actually, the front hub locks I've seen disconnect
the front hubs from the front axle, in the hub carrier itself, not at the
diff, which would still have the front driveshafts still turning with the
front wheels.

>This saves wear and tear on the front diff and forward drivetrain; it is not
strictly 
>necessary to disengage the hub locks, but leaving them engaged will cause 
>wear and waste fuel. 4WD's without external hub locks typically use a single

>vacuum-actuated hub lock to disconnect one wheel from the front diff; while
>easier to operate (no need to leave the warm and cozy cab), they are prone
>to problems, and cause additional wear.  I actually replaced the entire
front 
>axle of my '87 Jeep with a Dana unit that had external hub locks for this 
>reason (among others), but thats another story...

This vacuum hub lock is a new one to me.  The 4x4s I've seen/driven with
self-locking hubs usually unlock after disengaging 4wd then driving in
reverse for about 50 feet or so. 

Linus.
LToy@aol.com