Re: Bent frame rail

Posted by Mike Flanagan on October 01, 1997 at 23:16:13

In Reply to: Bent frame rail
posted by Glen Weilbaker on September 30, 1997 at 07:49:19

Glen, the other fellows are correct in what they say. From an engineering standpoint the frame rail is nothing more than a beam or structural member if you will, laterally restrained and supported at both ends and the middle and with concentrated loading at various points along it's length. DJ is correct, a great percentage of the concentrated loading is at almost the center of the span, add this to the fact that there are torsional components added because of the rear end being unsprung weight and it's vertical motion will induce additional loading... dam how come they ain't all bent?!
If the frame rail is not deformed (kinked) you can straighten it with a hydraulic jack and almost anything rigid enough to jack against. I have an old piece of 90 lb railroad rail that I use for a "stiff back". Two chains, one at each end, and the jack at the bend and you're in business. Use a "softener" between the frame and the jack if you are using the ram against the frame and put a wood filler inside the frame to fill the space between the top and bottom flange. Pump the jack until you are a little past and then let off and look see. probably take several tries until you get it perfect.
If you do have to weld the frame concentrate your welding so that the welds travel lengthwise on the frame, don't weld across either the flange or the web or "she's a gonna break"!
As to why it bent on one side and not the other? Coulda been the specific gravity of the significant other....
God speed under 50.
The Model A Fool.
: Why does the frame commonly bend at the rear motor mounts?
: I'm currently doing a frame off that has the passenger rail bent and the driver's straight. At first I thought maybe it was weak to carry weight and the bend occured over time, but why one side? When I replaced the rubber for the mounts, there was rust scaling into the rail behind the rubber but that was on the straight side which makes it even weaker, so I don't think weight could be the cause. Then I noticed the passenger frame horn bent, probably frome a fender bender. Could this be the cause? The reason I ask is I don't want to have a problem after the car is together that can be prevent now. Currently I'm planning to repair the rusted section which is only inbetween the 3 motor mount bolts and straighten the frame. Would this be ok or should I consider another option?
: GW

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