At 12:55 -0400 990423, Gary Thaxter wrote:
| As far as the life of the VC, I do not see that the fluid could loose it's
| properties with age, but contamination from seal failure will definitely
| affect it.

It certainly does lose its properties with age. I don't have a synchro, but
the Miata used VCs in the rear (only) differential. They last about 30k
miles before they start to work like an open diff. My impression (confirmed
by a card-carrying SAE member on the Miata list) is that the long polymer
chains that give the fluid its thixotrophic properties break down with
continuous shearing. Excess heat may also be a factor.

A "center diff" in a 4x4 will probably last far longer, since it's in shear
mode far less than a rear diff.

Mazda switched to Torsens after a few years, and even Mazda comp doesn't
sell a VC diff...they sell clutch-type limited-slip diffs for racers.

Just my $0.02

-Zandr
 '85 (2WD) Westy
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Aleksandr Milewski                                              N6MOD
n6mod@amt.org                               http://www.amt.org/n6mod/