Release the CRACKIN!!

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Model T Ford Forum: Forum 2016: Release the CRACKIN!!
Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Mclellan on Sunday, February 28, 2016 - 01:24 pm:

I'm guessing these are typical cracks for a Model T cab but figured I would post up just for possible opinions or advise.

Was it the stress on the hole, or just on the firewall itself that would have caused this crack?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, February 28, 2016 - 01:51 pm:

I would think body flex. The only thing going thru that hole is the choke rod. I would venture to say not normal. I flipped the photo.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Don Booth@ Bay City, Mi on Sunday, February 28, 2016 - 01:59 pm:

The 26 Tudor I'm working on had the same issue. The exact same spot and length.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Harper - Keene, NH on Sunday, February 28, 2016 - 02:04 pm:

Hi Robert,

If you can pull that crack close enough and tight enough together, you likely can TIG weld (without filler metal) that back together and the repair will be almost invisible. Good luck with your project. Bill


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Mclellan on Sunday, February 28, 2016 - 02:24 pm:

Interesting that your 26 had the exact same crack Don. Any thoughts of reinforcement from behind?

You may also notice in that picture, that the front floor cross brace has a funny notch cut out of it.

Any ideas of what that was for? I was going to weld a section back in seeing it is in about the worst spot for integrity.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Robison on Sunday, February 28, 2016 - 02:35 pm:

Typical crack for 26-7 bodies. The body was too ridged for the frame. In late production Ford eliminated the firewall to frame brackets, this helped. In very late bodies the holes weren't even punched in the body for the firewall bracket bolts. Weld it up, then leave off the firewall to frame brackets.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stephen D Heatherly on Sunday, February 28, 2016 - 02:40 pm:

My 26 coupe is cracked in the exact same spot. I drilled holes in each end of the crack to keep it from spreading.

Stephen


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, February 28, 2016 - 02:53 pm:

Re not normal; guess it is. Learn something new every day. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Don Booth@ Bay City, Mi on Sunday, February 28, 2016 - 03:17 pm:

Robert, I ended up running three weld beads to beef it up a bit. I still have to clean the inside area up but as you can see it seems to be a common stress area.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Sunday, February 28, 2016 - 08:03 pm:

That notch may be there for fitting a Warford or other auxiliary transmission. To fit my modern Warford I had to make a small notch (about half that depth) to have clearance.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Murray - Anacortes, WA on Tuesday, March 01, 2016 - 06:06 pm:

Me four...same cracking on 27 Coupe body. Actually, on both sides above the firewall to frame brackets.

TT


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Mclellan on Tuesday, March 01, 2016 - 06:10 pm:

So what is the consensus? Weld up the holes and forget about the brkts? (apparently a late model Factory option)

Or go with the theory that the T will never be driven on bad enough roads for extreme flex to stress firewall?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dick Fischer - Arroyo Grande, CA on Wednesday, March 02, 2016 - 12:15 am:

I have a slightly different "take" on the reason for the cracking. Follow me on this:

The stamping operation which formed the bead places the metal under tension. The cracks pictured are at the point of greatest stretch, thus greatest tension.

Now, the firewall didn't crack when formed, but there was no doubt a great deal of residual stress remaining in the part. When the part is placed into service, the added stress due to vibration and possibly the frame brackets just sort of pushes the accumulated stress over the top and you get cracks.

The cracks are basically the metal separating where the tension is greatest, thus relieving the stress. That's why there is a gap in the metal at the crack.

If you want to weld up the cracks, that's fine. But remember that the weld will shrink as it cools, and here comes the tension right back where it broke the first time.

Old time body repairmen performed what is called hammer welding. What that means is that the weld bead is hammered flat rather than grinding down. The reason for hammering is not so much to hide the weld bead as to place the metal in residual compression rather than in tension. Cracks don't form under compression; they form under tension. You can think of hammering the weld down as a poor man's shot peening.

After hammering the weld you will find that fatigue cracking is far less likely.


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