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When/why we need x-member bracing
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I'll check in here, Neal. 1987, 16v, 190K; no cracks.
(I DID have to make a new, lower front mount. Even with new side mounts =
the front was grossly misaligned and, consequently, was carrying an =
inordinate amount of weight)
Larry
----- Original Message -----=20
From: Neal Tovsen=20
To: T. Reed=20
Cc: Dan Bubb ; Scirocco List=20
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.=20
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.=20
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,
>=20
> That's a very interesting theory, and I did not know that the front =
mount
> was an add-on!
>=20
> 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..
>=20
> 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.
>=20
> -Toby
>=20
> On Tue, 4 Mar 2003, Dan Bubb wrote:
>=20
> > 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
> >
> >
> >
>=20
>=20
> _______________________________________________
> Scirocco-l mailing list
> 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
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<DIV><FONT face=3DArial size=3D2>I'll check in here, Neal. =
1987, 16v,=20
190K; no cracks.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>(I DID have to make a new, lower =
front=20
mount. Even with new side mounts the front was grossly misaligned =
and,=20
consequently, was carrying an inordinate amount of weight)</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Larry</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: =
0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A href=3D"mailto:nealtovsen@yahoo.com"; =
title=3Dnealtovsen@yahoo.com>Neal=20
Tovsen</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20
href=3D"mailto:treed2@u.washington.edu"; =
title=3Dtreed2@u.washington.edu>T.=20
Reed</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Cc:</B> <A =
href=3D"mailto:jdbubb@ix.netcom.com"=20
title=3Djdbubb@ix.netcom.com>Dan Bubb</A> ; <A=20
href=3D"mailto:scirocco-l@scirocco.org"; =
title=3Dscirocco-l@scirocco.org>Scirocco=20
List</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Tuesday, March 04, 2003 =
10:37=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> When/why we need =
x-member=20
bracing</DIV>
<DIV><BR></DIV>> > I have a theory here, so y'all get out your =
flame=20
throwers!<BR>> > The theory is based the fact that I've had my =
Scirocco=20
for 18.5 years and<BR>> > have always driven it hard. Not =
slamming=20
shifts, but alot of WOT and high<BR>> > RPM downshifts. In other =
words,=20
I've had as much opportunity to crack my<BR>> > chassis as =
anyone and to=20
date, with 240,000 miles, NO cracks.<BR><BR>I pulled this portion of =
the=20
crossmember thread into its own new thread. <BR>See the two relevant =
emails=20
below if you haven't been following.<BR><BR>I've been doing a lot of =
thinking=20
about WHEN and WHY the crossmember<BR>cracks appear, in combination =
with the=20
people who have actually said<BR>that they've experienced this=20
problem.<BR><BR>Is there ANYBODY out there who has an '84 or older =
Scirocco=20
with a<BR>cracked front crossmember? If there are any, I bet it's only =
a=20
couple<BR>people out of the bunch. I dawned on me one day that I =
haven't heard=20
of<BR>anyone with this problem on a Mk1 or on a pre-'85 car. Nearly =
all=20
of<BR>them have been 16v's, and I think the 8v's were later cars=20
too.<BR><BR>While it is obvious that improper alignment of the motor =
mounts=20
could be<BR>a contributing factor, there is one important thing that =
happened=20
after<BR>'84. In 1985, VW changed the floor pan of the car to =
incorporate=20
the<BR>space-saver spare tire and larger gas tank. At the same time, =
the=20
design<BR>of the car changed a little bit across the whole car. Most=20
importantly,<BR>the type of steel used was changed! It was supposed to =
be (and=20
is, from<BR>my experience) much more rust-resistant. This became clear =
when I=20
was<BR>welding the floor pan from an '85 into my '77, and was =
reinforced by=20
an<BR>autocrosser who isn't on this list who has also studied the =
floor=20
pans<BR>of the different year Sciroccos. <BR><BR>The '85 floor pan I =
had was=20
very obviously of different material, and I<BR>am starting to believe =
that it=20
is more prone to stress cracks.<BR><BR>The only other possibility that =
fits=20
this theory somewhat is that in '86<BR>we started seeing higher-output =
16v=20
engines. However, that doesn't<BR>explain all the souped-up 8v's and =
16v=20
transplants into earlier cars<BR>that seem to all do fine.<BR><BR>So =
let's=20
test the theory. Anybody out there with an '84 or older<BR>Scirocco =
with=20
crossmember cracks? Dan Bubb, what year is your =
car?<BR><BR>Neal<BR><BR>On=20
Tue, 2003-03-04 at 17:48, T. Reed wrote:<BR>> Dan,<BR>> <BR>> =
That's=20
a very interesting theory, and I did not know that the front =
mount<BR>> was=20
an add-on!<BR>> <BR>> I think you're probably right to some =
degree. But=20
take note that just<BR>> about every case of cracked crossmember =
I've seen=20
(and maybe people will<BR>> jump out here to prove me wrong - feel =
free!)=20
has been on a Mk2, usually<BR>> with a 2L 16v. And the cracks =
typically=20
develop within a year or two of<BR>> upgrading the engine. Those =
has just=20
been my observations, though. I'm<BR>> sure I'm gonna catch flak =
for saying=20
that..<BR>> <BR>> Personally, I think poly mounts are a big =
contributor.=20
I have a poly front<BR>> mount and a vw motorsports rear mount and =
when I=20
jump on and off of the<BR>> gas very quickly the whole car jerks =
around=20
like a friggin air hammer.<BR>> That kind of pounding has got to do =
bad=20
things to the thin sheetmetal<BR>> that vw spot welded together to =
form a=20
crossmember.<BR>> <BR>> -Toby<BR>> <BR>> On Tue, 4 Mar =
2003, Dan=20
Bubb wrote:<BR>> <BR>> > I have a theory here, so y'all get =
out your=20
flame throwers!<BR>> > The theory is based the fact that I've =
had my=20
Scirocco for 18.5 years and<BR>> > have always driven it hard. =
Not=20
slamming shifts, but alot of WOT and high<BR>> > RPM downshifts. =
In=20
other words, I've had as much opportunity to crack my<BR>> > =
chassis as=20
anyone and to date, with 240,000 miles, NO cracks.<BR>> > The =
two=20
powertrain mounts that do the most to dictate the position of =
the<BR>> >=20
engine are the side mounts. They sag with time. The rear and front=20
mounts<BR>> > can be adjusted to accomodate this sag to some =
extent.=20
But, if they're not<BR>> > adjusted they end up supporting most =
of the=20
weight when their main function<BR>> > (imho) is to resist =
powertrain=20
torque. So, if you never adjust your front<BR>> > and rear =
mounts and=20
don't replace your passenger side mount regularly, you<BR>> > =
have an=20
abnormal load on the front and rear mount. The front is the =
least<BR>> >=20
able to take the load, so cracking results.<BR>> > Did you all =
know the=20
front mount was an after thought. The Scirocco was<BR>> > =
originally=20
produced without a front mount. A retrofit was added to the =
'75<BR>> >=20
Scirocco, and the current mount design started in the '76.<BR>> =
> So,=20
that's my theory! Adjust and replace your powertrain mounts =
often.<BR>>=20
> Dan<BR>> ><BR>> > >If this were the case, why =
is<BR>>=20
> > my crossmember cracked on the bottom rather than the top? =
Tension=20
causes<BR>> > > cracking, not compression (or at least it =
takes a=20
great deal more<BR>> > > compression to crack sheet metal in=20
general)<BR>> > ><BR>> > > Could you clarify your=20
statement?<BR>> > ><BR>> > > Thanks,<BR>> >=20
><BR>> > > -Toby<BR>> > ><BR>> > > On =
Mon, 3 Mar=20
2003, Allyn wrote:<BR>> > ><BR>> > > > > First =
of all,=20
the force vector acting on the crossmember points<BR>> >=20
straight<BR>> > > > > down.<BR>> > > =
><BR>> >=20
> > umm, during a downshift perhaps, but the major load is in =
the=20
upward<BR>> > > > direction, during acceleration. i think =
this=20
makes your whole<BR>> > explination<BR>> > > > =
backwards (as=20
far as tensile/compressive stresses), but it will work<BR>> >=20
just<BR>> > > > the same.<BR>> > > > =
Al<BR>> >=20
> ><BR>> > > ><BR>> > ><BR>> > =
><BR>>=20
> ><BR>> > >=20
_______________________________________________<BR>> > > =
Scirocco-l=20
mailing list<BR>> > > <A=20
=
href=3D"mailto:Scirocco-l@scirocco.org";>Scirocco-l@scirocco.org</A><BR>&g=
t; >=20
> <A=20
=
href=3D"http://neubayern.net/mailman/listinfo/scirocco-l";>http://neubayer=
n.net/mailman/listinfo/scirocco-l</A><BR>>=20
><BR>> ><BR>> ><BR>> <BR>> <BR>>=20
_______________________________________________<BR>> Scirocco-l =
mailing=20
list<BR>> <A=20
=
href=3D"mailto:Scirocco-l@scirocco.org";>Scirocco-l@scirocco.org</A><BR>&g=
t; <A=20
=
href=3D"http://neubayern.net/mailman/listinfo/scirocco-l";>http://neubayer=
n.net/mailman/listinfo/scirocco-l</A><BR><BR><BR><BR>____________________=
___________________________<BR>Scirocco-l=20
mailing list<BR><A=20
=
href=3D"mailto:Scirocco-l@scirocco.org";>Scirocco-l@scirocco.org</A><BR><A=
=20
=
href=3D"http://neubayern.net/mailman/listinfo/scirocco-l";>http://neubayer=
n.net/mailman/listinfo/scirocco-l</A><BR></BLOCKQUOTE></BODY></HTML>
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