Date: Wed, 19 Oct 1994 15:28:40 -0400 (EDT)
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: sstones <sstones@io.org>
Subject: Re: Syncro Estasy, spins, ABS
On Tue, 18 Oct 1994, William Abbott wrote:
>
> > >BTW, the Synchro is an amazing option. With studded snows it is an
> > >awesome winter-mobile. Could use ABS, though, as my wife found out in a
> > >little spin out last winter.
ABS isn't going to help you much on snow. A lot of road friction is
needed to create enough of a wheel speed difference to make ABS function.
> > (Actually, the syncro doesn't need ABS since the viscous coupling tends to
> > distribute even braking force equally between the front and the rear of the
> > vehicle.)
With a functional brake proportioning valve and a well trained foot, one
can stop a car faster without ABS.
> Distributing braking force and ABS are two different things.
> ABS, usually, moitors wheel speeds and modulates the brakes to prevent
> any of the wheels from locking up. When it senses a wheel slowing down to
> a stop, it momentarily releases brake pressure on that wheel. Typically,
> ABS is fitted to 2WD vehicles, like my Corrado, but my friend Kevin has
> rear-wheel-only ABS on his GMC 3500 4WD. As the name suggests, it keeps
> the rears from locking, but doesn't affect the fronts. I'm not sure it
> works when in 4WD, and that brings us to the Synchro.
Yes, it works full time. The point of rear wheel ABS is so that pickup
trucks don't need their proportioning valve adjusted every time the load
in the back changes.
> As I understand 4WD, with limited-slip differentials, the wheel
> speeds are all related to each other. You can't stop one wheel and have
> the other three turn, or break one free and spin it. The effect is much
> like ABS but not exactly the same thing. You can loose traction, but you
> can't get too far from it on or two wheels at a time.
No that would be with differential locked diffs. limited slip
differentials will not allow wheels to turn at different speeds unless
the torque between them is enough overcome the diff setting. Therefore
as long as the driveshaft is turning, there is a minumum amount (diff
setting) of torque on whichever wheel is getting traction.
>
> So you can spin a 4WD vehicle, but you have to loose traction
> on all four wheels to do it.
Yes if the differentials are locked. If not, you can spin one front and
one rear simultaneously.
> Most typical spins are conducted by locking
> the rear wheels, which lowers their coefficient of friction compared to
> the fronts. If the driver holds the brakes on, the fronts, having more
> traction and thus generating more slowing force, will try to get behind
> the rears.
>
> On days of amazing rain, I've gotten my Corrado sideways by
> stomping on the brake and turning the wheel, but it takes effort and
> if you just let up, it goes straight.
This can also be accomplished with the parking brake... But it can't be
too good for your wheel bearings.
>
> I remember reading that a Synchro cannot be towed, since the
> drive train can't be disconnected and the system doesn't like to driven
> long distances with power flowing in from the wheels. This suggests that
> the Syncro is always in 4WD. Is that true?
Yes. The fluid coupling never lets up. The synchros rear wheels should
be placed on a towing dolly for towing.
>
> Cheers!
> Bill
>
> (What do you call a 4 humped camel in Jiddah?
>
> A Saudi Quatro!)
>
Sorry for writing a novel. But I wanted to make sure all was clear.
Cheers ***
SStones Toronto, Ontario. ** **
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