When/why we need x-member bracing

[Rabbit16v@attbi.com (Rabbit16v)]

Congratulations!!  You have figured out that manufacturers (in general, not
just VW) are ALWAYS trying to find ways to cut corners.  VW probably figured
that their cars were only lasting (on average) about 120 - 150K and figured
"why the heck should be make them to last 20 years when they don't last that
long".  So, they thin the metal a little, use a cheaper but theoretically
'just as strong' metal and viola!  A car that is cheaper to make, costs
more, more pocket padding!!  It isn't a new revelation that cars get cheaper
as they go.  Even the BMWs and Mercedes and Lexus, etc. more plastic, more
cheezy stuff etc.  Sure, they may be more comfortable but I remember when
Mercedes and BMW had REAL wood on the dashes and used leather on the sides
and backs of the seats too!  Or, didn't have everything that you touch made
out of plastic.  I bet that if you did the research you would find that they
put less into their cars these days even with all the creature comforts when
the cost of cars has gone up about 400% over the last 20 to 25 years.  I
would say, though, that of all the automotive companies that have been
around for 50 years or more, the German companies are the ones who still
take a lot of pride in their workmanship and, even though they make gobs of
money, seem to be more interested in turning out top of the line cars than
cutting the corners to make an extra penny per car.

I have owned some newer VWs (well, mid to late eighties) but would never
want to keep one.  I have and will always use late 70's VWs for all my
projects especially if they have any kind of frame twisting power!  Just my
opinion!

Dave
----- Original Message -----
From: "Neal Tovsen" <nealtovsen@yahoo.com>
To: "T. Reed" <treed2@u.washington.edu>
Cc: "Dan Bubb" <jdbubb@ix.netcom.com>; "Scirocco List"
<scirocco-l@scirocco.org>
Sent: Tuesday, March 04, 2003 10:37 PM
Subject: When/why we need x-member bracing


> > > 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
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > _______________________________________________
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> > >
> > >
> > >
> >
> >
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>
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