When/why we need x-member bracing

[nealtovsen@yahoo.com (Neal Tovsen)]

Well, they are definitely stress marks in the *paint*,
but that doesn't mean that the metal is cracking. It
could be from the metal underneath flexing, but it
could also be from moisture getting underneath and
separating the paint from the metal.

I have those already on my freshly painted raintray,
but I suspect it might have something to do with the
sledgehammer I took to it to clear the throttlebody.
:)

Is that near the motor mount? Looks like on top of the
radiator support...

Neal


--- Andrew Wong <mkii_84@yahoo.com> wrote:
> Neal would these be considered stress marks on my
> Scirocco.  Its an 84 Scirocco built in 12/83 so it
> has
> the small tank and full size spare.  Even though I
> am
> in Florida, that area has some rust frrom being a
> northern car so I am unsure of what these lines are.
> 
> My 84 is complety stock also
>
http://camo.flage.net/vag/view_photo.php?full=1&set_albumName=albuo48&id=P3050123
> --- Neal Tovsen <nealtovsen@yahoo.com> wrote:
> > > > I have a theory here, so y'all get out your
> > flame throwers!
> > > > The theory is based the fact that I've had my
> > Scirocco for 18.5 years and
> > > > have always driven it hard. Not slamming
> shifts,
> > but alot of WOT and high
> > > > RPM downshifts. In other words, I've had as
> much
> > opportunity to crack my
> > > > chassis as anyone and to date, with 240,000
> > miles, NO cracks.
> > 
> > I pulled this portion of the crossmember thread
> into
> > its own new thread. 
> > See the two relevant emails below if you haven't
> > been following.
> > 
> > I've been doing a lot of thinking about WHEN and
> WHY
> > the crossmember
> > cracks appear, in combination with the people who
> > have actually said
> > that they've experienced this problem.
> > 
> > Is there ANYBODY out there who has an '84 or older
> > Scirocco with a
> > cracked front crossmember? If there are any, I bet
> > it's only a couple
> > people out of the bunch. I dawned on me one day
> that
> > I haven't heard of
> > anyone with this problem on a Mk1 or on a pre-'85
> > car. Nearly all of
> > them have been 16v's, and I think the 8v's were
> > later cars too.
> > 
> > While it is obvious that improper alignment of the
> > motor mounts could be
> > a contributing factor, there is one important
> thing
> > that happened after
> > '84. In 1985, VW changed the floor pan of the car
> to
> > incorporate the
> > space-saver spare tire and larger gas tank. At the
> > same time, the design
> > of the car changed a little bit across the whole
> > car. Most importantly,
> > the type of steel used was changed! It was
> supposed
> > to be (and is, from
> > my experience) much more rust-resistant. This
> became
> > clear when I was
> > welding the floor pan from an '85 into my '77, and
> > was reinforced by an
> > autocrosser who isn't on this list who has also
> > studied the floor pans
> > of the different year Sciroccos. 
> > 
> > The '85 floor pan I had was very obviously of
> > different material, and I
> > am starting to believe that it is more prone to
> > stress cracks.
> > 
> > The only other possibility that fits this theory
> > somewhat is that in '86
> > we started seeing higher-output 16v engines.
> > However, that doesn't
> > explain all the souped-up 8v's and 16v transplants
> > into earlier cars
> > that seem to all do fine.
> > 
> > So let's test the theory. Anybody out there with
> an
> > '84 or older
> > Scirocco with crossmember cracks? Dan Bubb, what
> > year is your car?
> > 
> > Neal
> > 
> > On Tue, 2003-03-04 at 17:48, T. Reed wrote:
> > > Dan,
> > > 
> > > That's a very interesting theory, and I did not
> > know that the front mount
> > > was an add-on!
> > > 
> > > I think you're probably right to some degree.
> But
> > take note that just
> > > about every case of cracked crossmember I've
> seen
> > (and maybe people will
> > > jump out here to prove me wrong - feel free!)
> has
> > been on a Mk2, usually
> > > with a 2L 16v. And the cracks typically develop
> > within a year or two of
> > > upgrading the engine. Those has just been my
> > observations, though. I'm
> > > sure I'm gonna catch flak for saying that..
> > > 
> > > Personally, I think poly mounts are a big
> > contributor. I have a poly front
> > > mount and a vw motorsports rear mount and when I
> > jump on and off of the
> > > gas very quickly the whole car jerks around like
> a
> > friggin air hammer.
> > > That kind of pounding has got to do bad things
> to
> > the thin sheetmetal
> > > that vw spot welded together to form a
> > crossmember.
> > > 
> > > -Toby
> > > 
> > > On Tue, 4 Mar 2003, Dan Bubb wrote:
> > > 
> > > > I have a theory here, so y'all get out your
> > flame throwers!
> > > > The theory is based the fact that I've had my
> > Scirocco for 18.5 years and
> > > > have always driven it hard. Not slamming
> shifts,
> > but alot of WOT and high
> > > > RPM downshifts. In other words, I've had as
> much
> > opportunity to crack my
> > > > chassis as anyone and to date, with 240,000
> > miles, NO cracks.
> > > > The two powertrain mounts that do the most to
> > dictate the position of the
> > > > engine are the side mounts. They sag with
> time.
> > The rear and front mounts
> > > > can be adjusted to accomodate this sag to some
> > extent. But, if they're not
> > > > adjusted they end up supporting most of the
> > weight when their main function
> > > > (imho) is to resist powertrain torque. So, if
> > you never adjust your front
> > > > and rear mounts and don't replace your
> passenger
> > side mount regularly, you
> > > > have an abnormal load on the front and rear
> > mount. The front is the least
> > > > able to take the load, so cracking results.
> > > > Did you all know the front mount was an after
> > thought. The Scirocco was
> > > > originally produced without a front mount. A
> > retrofit was added to the '75
> > > > Scirocco, and the current mount design started
> > in the '76.
> > > > So, that's my theory! Adjust and replace your
> > powertrain mounts often.
> > > > Dan
> > > >
> > > > >If this were the case, why is
> > > > > my crossmember cracked on the bottom rather
> > than the top? Tension causes
> > > > > cracking, not compression (or at least it
> > takes a great deal more
> > > > > compression to crack sheet metal in general)
> > > > >
> > > > > Could you clarify your statement?
> > > > >
> > > > > Thanks,
> > > > >
> > > > > -Toby
> > > > >
> > > > > On Mon, 3 Mar 2003, Allyn wrote:
> > > > >
> > > > > > > First of all, the force vector acting on
> > the crossmember points
> > > > straight
> > > > > > > down.
> > > > > >
> > > > > > umm, during a downshift perhaps, but the
> > major load is in the upward
> > > > > > direction, during acceleration. i think
> this
> > makes your whole
> > > > explination
> > > > > > backwards (as far as tensile/compressive
> > stresses), but it will work
> > > > just
> > > > > > the same.
> > > > > > Al
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > _______________________________________________
> > > > > Scirocco-l mailing list
> > > > > Scirocco-l@scirocco.org
> > > > >
> > http://neubayern.net/mailman/listinfo/scirocco-l
> > > >
> > > >
> > > >
> > > 
> > > 
> > > _______________________________________________
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> > > Scirocco-l@scirocco.org
> > > http://neubayern.net/mailman/listinfo/scirocco-l
> > 
> > 
> > 
> > _______________________________________________
> > Scirocco-l mailing list
> > Scirocco-l@scirocco.org
> > http://neubayern.net/mailman/listinfo/scirocco-l
> 
> 
> =====
> -Andrew Wong 
> 1984 Black Scirocco
> 1987 White Quantum wagon
> 
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