Frame sag at rear engine mount

Steve Wastler said:
Yes, there is an article associated with the pic, i'm trying to make sence of the info on the back, hope to find the article.

Here is another of the trucks in a postal warehouse in Balt., first two are 29's third is a 31 cant see enough of the 4th. The 40's into the fiftys, the post office was pillaging the junk yards for parts to keep the fleet on the road....
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Steve - is it my imagination, or does the first truck in line have an unusually tall radiator neck ?

Frank
 
BRENT in 10-uh-C said:
We've discussed that some on here in the past, --and on the old Fordbarn forum ...and if you think about this a tad, some part of that frame had to stretch when the frame bent/sagged. Bending it in the opposite direction in an effort to straighten it only bends (compromises) the metal in yet another area. Understanding how to manipulate the metal by shrinking it to return it to its former dimension is the best way to repair this. In the time it takes to set up using jacks & rigging fixtures to hold the frame stationary, I can heat and shrink the lower chord of the frame rail and have all the strength back. A bent frame that is "repaired" by re-bending it will never be as strong as it originally was.

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Brent,
I'm AMAZED that this can be done by shrinking alone. How large a spot do you heat each time & about how hot? Also, what is your quenching procedure? Oh! and do you just shrink on just the upper flange? Thanks, Brent, Bill W.
 
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Thanks for all input on the frame sag issue. No it does not have Float-a -Motor engine mounts. It does however have the original pretty much squeezed out rubber. I am amazed of how much REAL rubber still exists in the way of tires and such things as motor mounts on some of this old iron. I also wholeheartedly believe that any good restoration should start with complete checking and straightening of the frame. The vehicle I am helping the owner with is strictly at this point a component by component project so he can drive it.
 
BILL WILLIAMSON said:
Brent,
I'm AMAZED that this can be done by shrinking alone. How large a spot do you heat each time & about how hot? Also, what is your quenching procedure? Oh! and do you just shrink on just the upper flange? Thanks, Brent, Bill W.
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Just hot enough to make water turn to steam.

As far as how large an area, if you look at the metal closely you can usually tell where it is bent/stretched. Another way is to use a laser or a string. Any area that it is sagging below the string-line usually means it has been stretched. The areas that have the most sag mean they are bent more, ...which will require more shrinking. You work one area at a time and allow it to cool to room temp. Whenever the frame rail shows to be straight again with the laser or string, you are done.


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BRENT in 10-uh-C said:
Just hot enough to make water turn to steam.

As far as how large an area, if you look at the metal closely you can usually tell where it is bent/stretched. Another way is to use a laser or a string. Any area that it is sagging below the string-line usually means it has been stretched. The areas that have the most sag mean they are bent more, ...which will require more shrinking. You work one area at a time and allow it to cool to room temp. Whenever the frame rail shows to be straight again with the laser or string, you are done.

.
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Brent thanks for the info & photos !

Are the heated areas are then quenched with a rag dipped in cool water, or just allowed to air-cool ?

Thanks !

SC Frank
 
Special Coupe Frank said:
Brent thanks for the info & photos !

Are the heated areas are then quenched with a rag dipped in cool water, or just allowed to air-cool ?

Thanks !

SC Frank
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Both, just depends on how much we need to shrink it, ...and in what areas. Without going into a huge write-up, just think of the rail side in the bent area as a "pie shaped wedge" with the point facing upward. The stretch is at the most at the bottom of the pie shape and graduates smaller up the side of the rail until the amount of stretch is at the least. Look at the heat pattern in the pix above and you will see what I mean. If you heat just the bottom and shrink only the bottom chord of the rail, water cooling is much more rapid than what the side area is going to shrink, therefore part of that area is trying to counter-act what you are working to accomplish with the shrinkage on the bottom chord. That is why we may initially use compressed air on the bottom chord while using water on the side before moving to water on the bottom chord to finish the cooling process.

.
 
When I was building cars for other people, many of them were Model A's. Every A frame was bent (sagged) and in the same place. There is 5 holes in the same area (rear motor mounts) and after many years of chuck holes and railroad crossing impacts the frame bent. With the many air holes in the frame it can move with no measureable change in frame size. It is easy to straighten cold (please no heat) Don 541 582-8966
 
The webs between the holes in the frame will shrink under compression on the bottom half of the frame the same way it did on the top half of the frame . This is why a metal worker (old body man) can straighten a dent in a fender, he shrinks the metal cold. Metal becomes a fluid under pressure and no out side heat should be applied. Only in extreme circumstances should heat be used and the sagged frame is not one of them. Have a good day.
 
OK now I'm confused, cold bending is stretching use heat but cold bending is compression don't use heat.

This is like asking who didn't flush the toilet at my house, I never hear a straight answer.
 
gweilbaker said:
OK now I'm confused, cold bending is stretching use heat but cold bending is compression don't use heat.

This is like asking who didn't flush the toilet at my house, I never hear a straight answer.
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Yeah, I agree. :D :rolleyes: Also notice how "all of them bend in the same place" did not apply to this frame in the pictures above. :confused:



 
I agree with Brent on this. Distortion is seldom the result of shrinking, but stress or impact induced stretching is generally found in these types of movement. Shrinking is an often mis-understood method and hard to achieve with most common tools, but is easily acomplished with a source of heat, good measuring and a basic understanding of what heat (at the correct temperature) and the subsequent cooling can accomplish.

My experiences do not mirror the thoughts of 1936Ford
 
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