Todd Francis wrote:
> 
> >  Then all four should match almost exactly, with the exception of about 3000
> > miles on the rear tires.
> >
> > Can I get by replacing the front 2 for the time being and do the rear tires
> > in about a month, or will that stress my VC????
> >
> > Do I have to have the exact same tread wear on all 4 or do they just need to
> > be the same size.
> > paul.holmdahl@lawson.com
> 
> Hi Paul,
>      I have a VW training manual that says "When the difference in
> speeds between the flange shaft and the pinion shaft is less than 6% the
> viscosity of the silicon fluid is low. This allows the plates to slip,
> resulting in no transfer of power between them. However, when the speed
> difference between the two shafts beccomes greater than 6%, which could
> happen if the rear wheels lost traction on a slippery road surface, the
> outer splined plates connected to the flange shaft begin to cut or shear
> the silicon fluid. The shearing action of the silicon fluid causes
> internal heat and results in a sharp increase of the fluid's viscosity.
> It becomes more difficult for the fluid to become sheared and the
> coupling locks up."  I suppose you knew how the viscous coupling worked
> but I was interested in what VW said about the 6% difference in speed. I
> wonder if the coupling will not lock up with the two shafts spinning at
> a 6% difference for a long distance?  I wouldn't want to try it. I think
> you should get the tires matched as closely as possible. The front diff
> is very expensive.
> 
> Todd Francis
> 91 Tristar
> 86 westy syncro

How much in tire diameter could 6% represent?
Peter Larsson
1994 EV Crewcab Syncro