Home » Public Forums » GMCnet » Frame Restoration:
| Frame Restoration: [message #150819] |
Sun, 27 November 2011 21:30  |
noi
Messages: 293
Registered: October 2010
Location: South of Fremont
Karma: 0
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Senior Member |
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Greetings:
I noticed something about my frame rails, as I was in the final process of rust de-scaling in preparation for sealing & coating, that I found interesting.
When I placed the two rails next to each other, to check for relative straightness, I was shocked to see that they were not totally parallel to each other - As I had “squeezed” the back half together first (random selection):
http://www.gmcmhphotos.com/photos/showphoto.php?photo=41619&title=rear-half&cat=5942
I then went to “squeeze” the front half together, to get a feel for how straight/parallel the rails were, and saw the “gap” that was there:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=41616&title=front-half&cat=5942
At first, I attributed this to the rails being “bent” due to repeatedly being jacked up in the “weak” area of the frame, as it was in the “wavy” section – As it looked to be “bent” in the opposite direction to body load, and would therefore “straighten out” as load was placed on it, I figured it wasn’t too bad and the worse effect would be to have a slight decreasing factor on caster.
Attempting to asses the “damage”, I stacked the rails on top of one another, to see which one was worse:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=41620&title=stacked&cat=5942
I was then very surprised to see that ALL the holes lined up, as far as I could visually see, exactly!
http://www.gmcmhphotos.com/photos/showphoto.php?photo=41617&title=holes-front&cat=5942
http://www.gmcmhphotos.com/photos/showphoto.php?photo=41618&title=holes-rear&cat=5942
I can only think of two, viable, reasons for this:
First, and most unlikely, the rails bent evenly from years of evenly applied forces.
Second, and what I think most likely, rails were built with a small bow in them to resist “sagging” and allow thinner/lighter material to be used – Much like the torsion bars are pre-stressed – I placed the “apex” of the bow on our driveway seam (yeah I know, not very scientific, but figure close enough) and it does appear that there is a slight bow in the rails.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=41614&title=bow-front&cat=5942
http://www.gmcmhphotos.com/photos/showphoto.php?photo=41615&title=bow-rear&cat=5942
Anyway, just something I found interesting – Look forward to any other thoughts or opinions.
Carl P.
76 Birchaven
South of Fremont
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| Re: [GMCnet] Frame Restoration: [message #150823 is a reply to message #150819] |
Sun, 27 November 2011 23:30  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Carl,
Get hold of Dan Stucky, he is the most knowledgeable.
I can have you take it to a shop and they will hit it on the hydraulic
press and straighten it for you.
Since yours is a 23', I tend to think that someone over lifted it in
that area at one time.
On Sun, Nov 27, 2011 at 7:30 PM, noi <v76_Birchaven@yahoo.com> wrote:
>
>
> Greetings:
>
> I noticed something about my frame rails, as I was in the final process of rust de-scaling in preparation for sealing & coating, that I found interesting.
>
> When I placed the two rails next to each other, to check for relative straightness, I was shocked to see that they were not totally parallel to each other - As I had “squeezed” the back half together first (random selection):
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=41619&title=rear-half&cat=5942
>
> I then went to “squeeze” the front half together, to get a feel for how straight/parallel the rails were, and saw the “gap” that was there:
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=41616&title=front-half&cat=5942
>
> At first, I attributed this to the rails being “bent” due to repeatedly being jacked up in the “weak” area of the frame, as it was in the “wavy” section – As it looked to be “bent” in the opposite direction to body load, and would therefore “straighten out” as load was placed on it, I figured it wasn’t too bad and the worse effect would be to have a slight decreasing factor on caster.
>
> Attempting to asses the “damage”, I stacked the rails on top of one another, to see which one was worse:
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=41620&title=stacked&cat=5942
>
> I was then very surprised to see that ALL the holes lined up, as far as I could visually see, exactly!
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=41617&title=holes-front&cat=5942
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=41618&title=holes-rear&cat=5942
>
> I can only think of two, viable, reasons for this:
>
> First, and most unlikely, the rails bent evenly from years of evenly applied forces.
>
> Second, and what I think most likely, rails were built with a small bow in them to resist “sagging” and allow thinner/lighter material to be used – Much like the torsion bars are pre-stressed – I placed the “apex” of the bow on our driveway seam (yeah I know, not very scientific, but figure close enough) and it does appear that there is a slight bow in the rails.
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=41614&title=bow-front&cat=5942
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=41615&title=bow-rear&cat=5942
>
> Anyway, just something I found interesting – Look forward to any other thoughts or opinions.
>
> Carl P.
> 76 Birchaven
> South of Fremont
>
> _______________________________________________
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> Unsubscribe or Change List Options:
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>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Frame Restoration: [message #150880 is a reply to message #150819] |
Mon, 28 November 2011 16:18 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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Senior Member |
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On Sun, Nov 27, 2011 at 10:30 PM, noi <v76_Birchaven@yahoo.com> wrote:
> Second, and what I think most likely, rails were built with a small bow in
> them to resist sagging and allow thinner/lighter material to be used
> Much like the torsion bars are pre-stressed I placed the apex of the
> bow on our driveway seam (yeah I know, not very scientific, but figure
> close enough) and it does appear that there is a slight bow in the rails.
>
I don't see enough bow to confirm in my mind that the dents from improper
jacking are not responsible. You have some kinking of the webs and that
will distort the shape a bit.
If there is supposed to be a bow, and I would rather doubt there is, I
don't think it's to allow a lighter section. I rather think it would be a
camber that deflects to straight under the weight of the body, to
facilitate fastening interior modules which have straight edges.
Rick "whose floor is absolutely NOT flat" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Frame Restoration: [message #150890 is a reply to message #150880] |
Mon, 28 November 2011 19:10 |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
Karma: 0
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Senior Member |
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I have the frame rails from my 26' handy. When I can find a bit of free time, I'll check to see if they have any bow in them. When I took the frame apart, I did do a quick comparison of the two rails, but I didn't pay any attention to the possibility of them being pre-stressed or bowed.
Les Burt
Montreal
On 2011-11-28, at 5:18 PM, Richard Denney <rwdenney@gmail.com> wrote:
> On Sun, Nov 27, 2011 at 10:30 PM, noi <v76_Birchaven@yahoo.com> wrote:
>
>> Second, and what I think most likely, rails were built with a small bow in
>> them to resist “sagging” and allow thinner/lighter material to be used –
>> Much like the torsion bars are pre-stressed – I placed the “apex” of the
>> bow on our driveway seam (yeah I know, not very scientific, but figure
>> close enough) and it does appear that there is a slight bow in the rails.
>>
>
> I don't see enough bow to confirm in my mind that the dents from improper
> jacking are not responsible. You have some kinking of the webs and that
> will distort the shape a bit.
>
> If there is supposed to be a bow, and I would rather doubt there is, I
> don't think it's to allow a lighter section. I rather think it would be a
> camber that deflects to straight under the weight of the body, to
> facilitate fastening interior modules which have straight edges.
>
> Rick "whose floor is absolutely NOT flat" Denney
>
> --
> '73 230 "Jaws"
> Northern Virginia
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: Frame Restoration: [message #151027 is a reply to message #150900] |
Tue, 29 November 2011 20:13 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""I think what was throwing me off was the fact that every single hole lined up – Even tiny ones – Just seemed like if the frame was bent from jacks and/or handling that there would be some side to side differences.
I’m pretty sure now Dan will confirm this when he responds – Guess the real question now is…. How bad is it! – And/or is it really even anything worth worrying about.
The CFO says “It’s lasted this long….Just treat it, paint it, and move on!!!!”
Les:
""
Although it is one of those intersting curiosities, it's not a swiss watch and I wouldn't remotely worry about it.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Frame Restoration: [message #151443 is a reply to message #150819] |
Sat, 03 December 2011 12:39 |
noi
Messages: 293
Registered: October 2010
Location: South of Fremont
Karma: 0
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Senior Member |
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Greetings:
OK, I have heard back from Dan Stuckey and he confirmed the collective wisdom of this forum….
As to the frame rails having a “bow” in them:
“GM did not build GMC frames with a bow in them”
And the forum assessment of frame rails “bent”:
“Your rails have sagged from the pounding and crashing over the potholes and “whoop-de-do’s” of life”
He did mention something I found interesting though, in regards to getting new rails or having current ones “straightened”, that I hope I can describe correctly.
After putting in the new rails, he had some “fun” getting the new stronger frame/front clip mounting support holes to align with “sagging” upper super structure mounting holes – Hope that makes sense.
Based on that, and the fact that I was able to pull the front support bolts out with little more than a vigorous hand grip-n-twist, pretty much indicates everything has settled into it’s current position quite well, and so will leave well enough alone!
Anyway, extrapolating forward, the “spot on” wisdom of the forum and the consensus that the frame rails look pretty good and not worry about them, it’s time to get back to “treat them, paint them, and move on”
Thanks for all the support!
Carl P.
76 Birchaven
South of Fremont
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