Positive Diff Locking

[QSHIPQ at aol.com]

The easiest way to design the diff lock actuators would have been with the 
vacuum/pressure pump (used in the door locks) to operate 1 side of the vacuum 
actuator diaphram (the other side open).  However, the design of the vacuum 
actuator switch and controller in the later cars is pretty failsafe in this 
respect.  All switched diffs will disable the lock-on controller when the key 
is turned off (a feature I didn't even know I had till the ops ck).  The diff 
lock on mode activates a vacuum relay that defaults to diff lock off with 
either a hit of the switch, a hit to ground (blue/white wire - signal from 
ecu), an overheat condition (within the controller, I didn't get it to 
activate, but under the seat it might), or a ignition kill.  This is a spring 
loaded relay, that will always default to the off position, which by 
definition, is vacuum to the diff actuator *unlock* side.

Since abs function is hooked to the actual diff lock actuator switch (at the 
diff), not the switch on the dash/between the seats, I really don't think you 
could ever have abs and rear diff lock at the same time.  That said, thinking 
about it, not sure what difference it would make, in a 3channel abs system, 
the rear wheel with the least traction is the signal the abs is functioning 
both rears with anyhow.  So, I doubt a problem in a straight line, a huge 
problem in a turn.

HTH

Scott Justusson
'83 tqc with 2 diff lock controllers from UrS4
In a message dated 2/14/01 2:12:21 PM Central Standard Time, 
Steven.Buchholz at kla-tencor.com writes:

> > > Naw, I believe the 15mph disable was cuz people forget to 
>  > do stuff.  I can't 
>  > 
>  > Yep, stops 'em scrubbing off the tires by leaving it locked and
>  > whining about that funny noise from the rear...
>  > One of the more likely explanations I've heard.
>  
>  ... agreed, it also minimizes the chances that the driver would be 
operating
>  the car for a long period with the ABS disabled ... although I wonder if
>  under braking in a panic stop situation if the diff lock could re-engage 
and
>  disable the ABS!  I'm not familiar with the inputs to the diff lock module,
>  but I've got to believe that is one they would have thought about ...
>  
>  Steve Buchholz
>  San Jose, CA (USA)