Transmission questions

[urq]

urq wrote:
> .... I believe they are referring to the gear ratios inside the
transmission,
> but you are correct that having unequal FDRs in the diffs can cause
> excessive differentiation in the center diff, which may cause excessive
> wear.  
> 
> I owned a 5000 TQ which had different ratios in the front and rear diff
.....
> I didn't figure that out before buying the car ... I don't know how long
the
> car had this configuration, but it didn't show any signs of center diff
> wear.  

Huw's Response:

I think the main "problem" with "continuous differentiation" (other than 
it sounds like tough calculus?) is that power is being transmitted by 
the small spider gears all the time, and they aren't really built for 
that.  In straight line travel, for instance, they only keep the output 
gears in sync, other than that they are just along for the ride.
==========

.... the power going to the ground has to go through those small spider gears
all the time ... except on lockers when the locking mechanism is engaged... 

Other than the obvious fact that you can't lock the center diff if the FDRs
of the front and rear differentials aren't matched, the best argument that I
had heard for balancing was that the bearings allowing the spider gears to
turn are sleeve bearings, which can wear significantly more than ball or
roller bearings ... so eventually the bearings will wear.  Audi must have
been worried about this too because they recommend that even quattros
without center torsens not be towed long distances with one pair of wheels
on the ground and the other pair stopped off the ground.  

I found a nifty website which includes animations of why a differential is
needed and different variants of differentials ...  

	http://www.howstuffworks.com/differential.htm

In the article on Torsens it indicates that the HumVee has a Torsen in the
front ... I guess some folks install Quaife's in front on their VWs too, so
it must not be too bad ... 

Steve B
San Jose, CA (USA)