Date:         Fri, 27 Dec 1996 19:04:28 -0800
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Todd Francis <tbf@pacifier.com>
Subject:      Re: Tires - Syncro (frequently discussed)

>  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