Date: Wed, 17 Dec 1997 17:16:13 -0800
Reply-To: Malcolm Holser <mholser@ADOBE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.sdsc.edu>
From: Malcolm Holser <mholser@ADOBE.COM>
Subject: Re: Dead VC
> Malcolm, re-read my post, I worded it awkwardly. I said
No, you worded it fine -- I read it awkwardly, and then quoted your
appropriately worded post in my flame -- I do apologize.
I don't have any help to offer you on whether your new VC is any
better than the old one before you put it in. I don't even know for
certain that the one I just replaced is good -- it does not "scrub"
in tight turns like my other syncro. The new VC felt entirely solid
before I installed it -- I don't think you can turn the two ends
relative to each other at all.
[ Ok, I went out and straddled a berm -- right front and left rear
tires on the berm, the others sitting in mud. Truck was stuck,
with the left front tire spinning -- the VC was therefore locked.
The right rear tire was spinning helplessly as well, a classic
four-wheel-drive-stuck-in-the-mud situation. It was very easy to
get the thing stuck (although I confess that I've gotten my LandCruiser
stuck soooo often that I know how to get there -- LandCruisers, especially
the old FJ40's like mine are real four-wheelers!). This VC does *not*
scrub in turns, but it does lock -- and 4-wheel drives still can get
stuck pretty easily if you try. The diff lock is sure a nice touch,
wish my LC had a couple of 'em, but then again it has a mondo stock
winch.]
The VCs are reputed to have changed over the years as well, with
variations on how quickly they lock up. Given the rather surprising
fact that they lock up *at all* I would suspect that they are kind of
individual about their actual behaviour. The lock point is apparently
a combination of the type of oil used internally, the machining of the
multi-plate clutch surfaces, the size of the air-bubble inside, the
internal initial pressure, and the temperature. With so many factors
involved, predicting the point they lock would be very hard.
My '86 Kombi was a fairly early example. I believe it has its original
VC, and it locks in any tight turn, annoyingly so. My '86 Doublecab is
the same vintage (probably built the same day) and its VC had been
removed, presumably because it had failed, although it was a dealer car
all its life, and a dealer might have stolen it temporarily to get a
customer's car running again. The new VC is not very aggressive compared
the Kombi.
Check the old archives, but I recall that Tim Smith had done some research
into the changes that the manufacturer of the VC did over the years. I
remember something about both making them less aggressive in the initial lock
(locking later) and locking stronger. This was apparently accomplished by
making the air bubble larger and pre-pressurizing the VC. It sounded like
they experimented a lot. I also recall that some other company did the VC,
but the one I put back in had only SDP on it in the end castings.
I have heard that they fail as you have described yours if the internal oil
is contaminated by seal failure. The failure allows the internal silicone
oil to leak out instead of holding the very high pressure needed to lock the
VC, and when it cools, allows hypoid differential oil to be drawn into the VC.
I would expect this sort of failure to eventually lead to a VC that allows
the front wheel to turn, but still with very stiff resistance, slowly getting
less stiff over time as the silicone oil became increasingly contaminated.
The failure to lock, however, would occur long before any difference would
be felt at the wheel, I would think.
As to the idea of a torque-wrench, well, it is a nice try, but the reality
is that even if the VC has good stiff resistance, the weirdness that causes
the locking may not be working. Having one *lock* is a good indication,
having one stiff to turn is only information that at least your VC has not
be ripped out, like mine was. The final problem with the torque wrench idea
is that the stiffness is that of a stiff fluid -- if you apply any torque
the thing will turn -- just not very fast. More torque, and it will turn
faster. So you would need a torque vs. rpm kind of test (and why the tools
for setting bearing preloads are so fancy).
malcolm
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