[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
'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.
> Justin Riley
> 1985 Ur-q
More information about the Torsen