[torsen] Re: [urq] When to use Diff Locks? - Kinda long

QSHIPQ at aol.com QSHIPQ at aol.com
Thu Nov 9 14:56:28 EST 2000

Ok, I'll jump with a few hundred thousand miles of btdt.  Here's how I sees 
For performance driving (and I mean anywhere), lock the center diff, always.  
Audis rally drivers never ran without the center diff locked, in fact, once 
Audi Sport figured that out, the center diff was deleted alltogether for 
weight reasons.  The biggest advantage to center diff locked is the ideal 
brake force distribution as a side benefit of the action.  I have one article 
that shows Mikkola actually had snapped his rear brake lines, and his service 
had to tell him, he didn't even know.  

The rear locker needs to be explored more, and the word "depends" comes to 
mind for me.  IME at Steamboat, I find that with good traction, unlocking the 
rear coming into the turns, hitting the apex, then locking coming out of the 
turns gave the best lap times (and I did win SCCA's first Rallycross at the 
steamboat venue using this method).  However, once things got really 
slippery, I just ran both the center and rear locked always.  FYI, as a rule, 
all rally cars from the late 80's on were locked center and rear, front open 
or LSD (includes the MTM/SMS/AS FIA 95 Group A rally car Bob D navigates).  
This includes tarmac stages.  There has been some debate on the use of 
torsens, but suffice it to say that even today (see Lawson's Vegas report on 
the new S4 on tarmac), that locked C/R still wins championships.  I 
interviewed Stig Blomqvist last year at Maine Forrest (1984 WRC champion), 
and he ran locked C/R always, and changed fronts depending on conditions 

I know Mr. Powell uses a locked rear in his racing efforts with center open, 
but historically, Audis race cars run center locked all the time, rear as 
driver preference.  The understeer with rear locked is pretty severe, so is 
tire wear.  That said, if you are putting a bunch of power down (or reducing 
cf, it's the same thing), locking both is the way to fly.  On all my 
quattros, I lock center always, then go after the rear if conditions are 
right, and do this routinely on the fly depending on the conditions coming up 
in the windshield.

Rear Locking...  What I have found is that the vacuum lockers can be 
manipulated to operate in your favor, and you can actually set a predictable 
cadence of lock/unlock.  The vacuum actuators are looking for a equal 
rotation of driveshafts to un/lock, and what I tend to do is blip the 
throttle right before entering a turn to unlock, and give breakaway throttle 
up blip just before engaging the lock, which then tends to lock as the revs 
come back down.  With good practice, you can peg exactly when the diffs will 
lock/unlock, which is the key to really enjoying their advantages.  That 
said, a lot is going on at Steamboat (or rallying or offroad performance 
driving), adding conscious locking and unlocking to that can be serious 
multitasking.  With that in mind, I plan on adding a rear diff switch to the 
shift knob of all my quattros, starting with the 83urq.  

If you don't mess with the lockers, you really haven't fully explored the 
quattro advantage IMO.  My advice to most is get that center locked and 
adjust for the additional understeer in driving technique, then add the rear 
to the equation.  Many have different preferences, but speed, control and 
*predictability* is really why audis race drivers prefer C/R locked in 
quattro chassis.

My .02
Scott Justusson
lockers aplenty
'87 5ktqw (lockers)
'87 4Runner turbo (lockers)
'84 Urq (lockers)
'83 Urq  (lockers)

In a message dated 11/9/00 12:10:45 PM Central Standard Time, jr at prefer.net 

> Hi all,
>  All of this discussion about Diff Locks has me wondering, when should they
>  be used?
>  More importantly, when should they NOT be used?  Are there any speed
>  limitations on engaging or disengaging the locks?  Should the locks ever
>  disengage themselves, ie  above a certain speed?
>  I am sorry for the list of what may seem to be nuisance questions, but I
>  have not yet obtained an original owners manual.
>  TIA
>  Justin Riley
>  1985 Ur-q

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