LSD on 105's

[yvesbou@mail.francomedia.qc.ca (yves boulanger et liette robin)]

First: in reply to Pierre Pfeffer: a stock 105 Alfa without limited slip is
no fun at all on a race track. In the tight parts, you spend your time
waiting for the inner wheel to regain traction before you can apply any
power. Except in very slippery conditions, a stock limited slip is perfectly
manageable. Also see below.

Second: in #18, J Hertzman brings an article by Paul Tenney regarding the
track behavior of a RACE PREPARED limited slip. It hasn't been pointed out
in the recent discussions that the ZF Lok-O-Matic LSD can be set for various
torque transfer ratios. It was originally supplied on new Alfas with a 25%
setting  which means that when one wheel starts spinning, 25% of the torque
supplied to the spinning wheel is transfered by the LSD clutches to the
other wheel. You end up with 37.5% (50% minus 25% of 50%) of the torque on
the spinning wheel, and 62.5% on the wheel that's got traction. Since the
torque the engine can develop is still limited by the spinning wheel, the
net output is still fairly limited. It's a far cry from a Detroit locker
intended for quarter mile activities. For racing, other settings of up to
75% can be used.  Optionally, springs (large Belleville washers) were
available to pre-load the clutches and provide an immediate response;
according to the information I got, they were not specified for the OEM Alfa
application. Resetting the LSD may be as simple as taking it apart and
putting the clutches back in in a different order. Different discs are also
available, and specific instructions are available from ZF or, I think, in
the old Alfa "Race preparation manual". Dismantling the LSD is not
complicated; nothing will fly in your face as you remove the cover. Just
take care to note the order in which the parts are stacked. If any parts are
replaced, a measurement has to be made to select the correct discs amongst
various thicknesses available; it's a shimmed assembly, like any other ZF
product. If ZF bottled Coca-Cola, they'd find a way to shim the caps.

Third: I dug out some period sales litterature. In a 1972 tech data sheet on
the new, US spec 2000's, the LSD is listed as a standard feature. Somebody
changed his mind, because a november 1972 price list  from Alfa Canada
quotes a $125 extra for the LSD. The 2000 US sales brochure (the large one
with the silver cover) describes the LSD as an option, and so do ads in Road
& Track (see Oct. 1974) which offer the LSD for $145 extra.  A further
folder, not dated but obviously 1974 judging from the bumpers on the
Berlina, sheds more light: the limited slip is described as a SAFETY FEATURE
(obviously written by somebody who never drove one in snow) and as a
REQUIRED EXTRA COST OPTION. Hence the confusion. I would assume that all US
bound 2000's had it.

Fourth: on the available ratios. Nobody picked up the challenge of
identifying the application of the 3.91 ratio; it doesn't exist! I really
meant 3.73, which is the ratio for an Automatic 1750/2000 Berlina. What's on
the Perndl Spiders?

Y. Boulanger