Front Body Frame Pictures

Rdenney

Rdenney

Well-known member
Dec 29, 2005
6,270
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48
NoVA
j harper writes...

> I don't think they came from the factory like that. I'm basing that
> on a statement Dave G. about never owning one with cheeks and you've
> been to enough rallies to have seen non-cheeked coaches.

I can't help it. I'm one of those engineering types who just expects
to find an explanation for something physical. And I can't find an
explanation for why MY coach has cheeks. I don't believe it's those
donuts, because I think the body frame would hold those points in the
air until the pads under the house sagged. And if your chassis
sub-frame is really settled at the front clip joint as you think it
is, that would actually absorb some of the slack caused by squished
donuts.

But I would not be prepared to say for sure how they came from the
factory. They changed the design of the front body structure once in a
major way, and we all know that FRP is not always stable or
dimensionally perfect. I have big waves in the fiberglass below the
waistline on the left side, which I've seen on lots of coaches. I'm
quite prepared to believe that some of them had cheeks and some of
them didn't. I can find no reason at all to be worried about mine.

I see an awful lot of compressive stiffness and strength between those
donuts and the rail at the base of the windshields, and things don't
sag in compression without being loaded to near their yield strength
and then pounded. Bending, maybe; that was Arch's concern about that
front beam. But the firewall has a lot of web strength and attaches to
that beam over its whole length. I'm more prepared to believe that
this particular fiberglass skin didn't quite fit this particular
welded-up body frame, and making it fit made it bulge a bit. I would
also be prepared to believe that sometimes it fit better than other
times. Maybe I would think differently seeing someone else's coach.

Sure, you can pull in those cheeks and nail them down, but I'm just
not sure what that really accomplishes, except to make the fiberglass
even more at part of the rigidity of the structure. And frankly I
don't see that as an argument in its favor.

Rick "suspecting the cheeks and the windshield gap are unrelated"
Denney

'73 230 Ex-Glacier "Jaws"
Northern Virginia

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Gcbr writes...

> Take a look at this. The cockpit floor is at the height of the lower
> rail of the space frame. Notice how the triangles are formed.
> Notice where the stress points are. Once you move out of the cockpit
> area the whole design changes. The cockpit is a cantilever without
> frame support.

Arch, notice how the bottom point of the forward triangle in the
picture meets that transverse rail. That rail is welded ever few
inches to the firewall. The shape of the firewall adds tremendous
stiffness to that horizontal rail.

Also, the fiberglass is primarly supported along the rail you see in
the picture that runs along the bottom of the windshield. That rail is
continuously attached to the flat part of the firewall, and the
90-degree angle between the vertical part of the firewall and the flat
part is gusseted by the AC blower box. Thus, you have a very strong
skin structure between that beam in the floor and that rail at the
bottom of the window.

The truss on the wise, coupled with the gusseting effect of the side
windows (which are, of course, missing in that photo), will actually
keep that frame suspended in mid air quite effectively. So, even if it
is cantilevered, it's a strong frame with good web depth and either
triangulation or skin strength.

But it is not cantilevered, but it is supported at its strongest point
(along the welded joint between the firewall and the floor beam) by
two tripod mounts.

I don't think it's the house frame that suspends the cockpit frame. I
think the cockpit frame and the house frame are quite strongly
designed, and those donuts hold up both. If the donuts sag, the whole
body will move as a unit, in my estimation. I think you could rest the
whole body of the GMC on the two front and two rear donuts without
appreciable deflection, unless something is broken.

If the firewall was not attached to that floor beam, then I would
agree that the beam would be weak against bending between the side
frame and the chassis mounting struts. But it would be dang nigh
impossible for that beam to sag without major buckling of the
firewall, which would be quite conspicuous and which I think would
require impact damage.

Rick "calling it like he sees it" Denney

'73 230 Ex-Glacier "Jaws"
Northern Virginia

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Rick

I'm going to assume you checked the weld between the firewall and the floor
beam at its outer most point and saw no deformation. So if what your saying
is correct then I come back to the correct spacing between the floor frame
and the front clip frame. The rubber pad. I also have the air cleaner
impression on the hatch cover installation. That would say that the floor in
sagging onto the engine itself. The only thing that would correct that would
be having a rubber pad of the correct (unshrunk) thickness. I keep coming
back to the rubber pad. How thick was the original rubber pad? anybody know?

john

----- Original Message -----
.
>
> But it is not cantilevered, but it is supported at its strongest point
> (along the welded joint between the firewall and the floor beam) by
> two tripod mounts.
>

>
> If the firewall was not attached to that floor beam, then I would
> agree that the beam would be weak against bending between the side
> frame and the chassis mounting struts. But it would be dang nigh
> impossible for that beam to sag without major buckling of the
> firewall, which would be quite conspicuous and which I think would
> require impact damage.
>
> Rick "calling it like he sees it" Denney
>
> '73 230 Ex-Glacier "Jaws"
> Northern Virginia

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Rick

"unless something is broken." or bent. Remmeber the picture of the wreck and
the weak point being pointed out to us

http://www.gmcmhphotos.com/gallery/showpic.php?uuid=jharper&aid=1018&pid=14836

john

----- Original Message -----
.
>
> I don't think it's the house frame that suspends the cockpit frame. I
> think the cockpit frame and the house frame are quite strongly
> designed, and those donuts hold up both. If the donuts sag, the whole
> body will move as a unit, in my estimation. I think you could rest the
> whole body of the GMC on the two front and two rear donuts without
> appreciable deflection, unless something is broken.
>

> Rick "calling it like he sees it" Denney
>
> '73 230 Ex-Glacier "Jaws"
> Northern Virginia
>

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Let me add one more check point for "body sag": For a long time after I began
to drive my coach, I would occasionally get a loud "clunk" from somewhere up
front. It didn't happen frequently enough or sound ominous enough for me to be
too concerned about it. Then one day with my son riding with me to test
something it really got bad on a dirt washboard road. He and I took turns
walking alongside until we finally located the source: The driver's front
"fender" was hitting the steering box. My solution was accomplished with a fine
saber saw blade. I don't know whether the interference was caused by sagging of
the front end or not, but I have noticed a couple of other rigs with the same
problem and it certainly is not factory standard. Some of you may want to see
how much clearance your fiberglass has from the steering box.

Rick, Cantilevered: With the front struts in place, and your discovery of the
attachment between the fiberglass and the firewall, I guess I shouldn't say the
cap's cantilevered, huh? How 'bout if we leave the donuts loose? :-)

I can't get real excited about my chipmunk either. Heck, I got paint peeling
off of my PL caulk -- that looks lots worse. :-(

Ken H.

> -----Original Message-----
> > I don't think they came from the factory like that...

> I can't help it. I'm one of those engineering types who just
> expects to find an explanation for something physical...
> Rick "suspecting the cheeks and the windshield gap are unrelated"
> Denney

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John,

I haven't checked my air cleaner - hatch clearance since I replaced the rubber
body spacers last month. But, from the movements I saw as I've done the various
tasks over the past few months, I'll bet dollars to donuts that those main body
spacers made far more difference to the cleaner-hatch clearance than did the
strut donuts. Replacing those compressed-to-1/8" pads with new 3/4" pads all
over the main frame made a dramatic difference. I noticed no difference from
installing new front donuts. Admittedly, when I installed the donuts, the front
frame clip was suspended from the main frame joints, so the strut clearance was
at its maximum.

Ken H.

> -----Original Message-----
>...I keep coming back to the
> rubber pad. How thick was the original rubber pad? anybody know?
>
> john

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Rick

Here's an interesting observation for your point. Look down the belt line
and you see where it bends up but then you can also see where it straighten
back out. The point where it straightens back out is approximately at the
same location as the strut. Everything forward of that is back in line. The
bend appears to be from the weak point (steps at cockpit to the struts).

http://www.gmcmhphotos.com/gallery/showpic.php?aid=1018&uuid=jharper&pid=14829

john harper
'77 kingsley

----- Original Message -----
From: "Rick Denney"
>
> But it is not cantilevered, but it is supported at its strongest point
> (along the welded joint between the firewall and the floor beam) by
> two tripod mounts.
>

>
> Rick "calling it like he sees it" Denney
>
> '73 230 Ex-Glacier "Jaws"
> Northern Virginia

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Ken

Ok you got me up off my butt and I went and measured. They appear to be
slightly less than 3/8th". If there is any compression on them It does not
appear to be much. Burt apparently sells 2 different thickness ( thick and
thin). Based on what Emery said about his '77 using thin I assume my '77
would use thin. 3/8th" sounds like thin to me. But nowhere close to 1/8".

Now when your talking about replacing the old pads with 3/4" pads and new
donuts your talking about your X-Birchaven? right. And it still has cheeks,
right.

john harper

----- Original Message -----
From: "Ken Henderson"

Replacing those compressed-to-1/8" pads with new 3/4" pads all
> over the main frame made a dramatic difference. I noticed no difference
> from
> installing new front donuts.
>
> Ken H.
>

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Thanks Ken I have been looking for that occasional clunk for 20 years, I
hope that is it.

Dan & Carol Winchester
78 Royal
Portland, OR
gmc.dwinchester.com


> -----Original Message-----
> From: Ken Henderson [mailto:hend4800]
> Sent: Saturday, November 12, 2005 5:38 PM
> To: d.l.winchester
> Subject: RE: Re[2]: [gmclist] Front Body Frame Pictures
>
> Let me add one more check point for "body sag": For a long time after
I
> began
> to drive my coach, I would occasionally get a loud "clunk" from
somewhere
> up
> front. It didn't happen frequently enough or sound ominous enough for
me
> to be
> too concerned about it. Then one day with my son riding with me to
test
> something it really got bad on a dirt washboard road. He and I took
turns
> walking alongside until we finally located the source: The driver's
front
> "fender" was hitting the steering box. My solution was accomplished
with
> a fine
> saber saw blade. I don't know whether the interference was caused by
> sagging of
> the front end or not, but I have noticed a couple of other rigs with
the
> same
> problem and it certainly is not factory standard. Some of you may
want to
> see
> how much clearance your fiberglass has from the steering box.
>
> Rick, Cantilevered: With the front struts in place, and your
discovery of
> the
> attachment between the fiberglass and the firewall, I guess I
shouldn't
> say the
> cap's cantilevered, huh? How 'bout if we leave the donuts loose? :-)
>
> I can't get real excited about my chipmunk either. Heck, I got paint
> peeling
> off of my PL caulk -- that looks lots worse. :-(
>
> Ken H.
>
> > -----Original Message-----
> > > I don't think they came from the factory like that...
>
> > I can't help it. I'm one of those engineering types who just
> > expects to find an explanation for something physical...
> > Rick "suspecting the cheeks and the windshield gap are unrelated"
> > Denney
>
>
> ---
> To unsubscribe send a blank email to mailto:unsubscribe-
> gmclist
>

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John,

It certainly sounds as if your isolators have stood up a lot better than mine
because mine were all compressed to 1/8", as measured after removal.

I made no attempt to determine or duplicate the original isolators. Ray
Swartzendruber bought a "cow mat" (a bovine stall floor pad) a couple of years
ago and bandsawed it into approximately 3"x6" rectangles. While probably firmer
than the original material, that rubber was soil for about 3/8" then ridged 1/8"
open/1/8" closed for the remaining 3/8" of its thickness. The pads hardly
compressed at all when the body was set on them.

Replacing the pads had no obvious effect on the minor chipmunk cheeks.

I don't seem to be seeing the same problem you do on your beltline molding
pictures. To me the vertical waves look like misalignment of the stuck-on trim,
not distortion of the aluminum strip to which it's attached. Are you seeing the
aluminum bend as you describe the molding bending?

Ken H.

> -----Original Message-----
> Ken
>
> Ok you got me up off my butt and I went and measured. They
> appear to be slightly less than 3/8th"...

> Now when your talking about replacing the old pads with 3/4"
> pads and new donuts your talking about your X-Birchaven?
> right. And it still has cheeks, right.
>
> john harper

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> -----Original Message-----
> ...
> the original material, that rubber was soil for about 3/8"
> then ridged 1/8"
> open/1/8" closed for the remaining 3/8" of its thickness.
Actually, it was more like solid than soil ...

Ken H.

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If we knew the manufacturing process that GM used to form the
fiberglass panels ( if the press was not hot enough or some other
reason the panel did not take the proper shape or the guy doing the
final shape didn't do his job) and process they used to size them
after they were formed we could come to some better conclusions, as to
the quality control, size and shape, tolerances make a big difference.
The bulge could be an over size panel that has been under stress and
after all these years decided to bulge.

If the workmanship of the fabrication is like the welds a lot of
things could be happening. look at their attempt to insulate the
interior. We are talking about auto assemblers doing aircraft type
fabrication, not a good thing. How ever the GMC is still better
product than you can buy then and now, RV wise.

Carleton

> John,
>
> It certainly sounds as if your isolators have stood up a lot better than =
mine
> because mine were all compressed to 1/8", as measured after removal.
>
> I made no attempt to determine or duplicate the original isolators. Ray
> Swartzendruber bought a "cow mat" (a bovine stall floor pad) a couple of =
years
> ago and bandsawed it into approximately 3"x6" rectangles. While probably=
firmer
> than the original material, that rubber was soil for about 3/8" then ridg=
ed 1/8"
> open/1/8" closed for the remaining 3/8" of its thickness. The pads hardl=
y
> compressed at all when the body was set on them.
>
> Replacing the pads had no obvious effect on the minor chipmunk cheeks.
>
> I don't seem to be seeing the same problem you do on your beltline moldin=
g
> pictures. To me the vertical waves look like misalignment of the stuck-o=
n trim,
> not distortion of the aluminum strip to which it's attached. Are you see=
ing the
> aluminum bend as you describe the molding bending?
>
> Ken H.
>
> > -----Original Message-----
> > Ken
> >
> > Ok you got me up off my butt and I went and measured. They
> > appear to be slightly less than 3/8th"...
>
> > Now when your talking about replacing the old pads with 3/4"
> > pads and new donuts your talking about your X-Birchaven?
> > right. And it still has cheeks, right.
> >
> > john harper
>
>
> ---
> To unsubscribe send a blank email to mailto:unsubscribe-gmclist=
net.org
>

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Ken

Yes, the entire beltline (aluminum casing and black plastic) is bending. It
runs straight then up then straight again ( as from back to front).

I suppose I could actually measure it by using a long 2x4 as a straight edge
on the back section and measure the distance between the straight edge and
the molding at the front. Maybe I'll do that tommorrow.

john

----- Original Message -----

Are you seeing the
> aluminum bend as you describe the molding bending?
>
> Ken H.
>

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