I have to concede that my frame is sagging,is there any way to fix it without removing the engine and body?
John, it may be possible to do the job if you can tie down the front and rear of the frame rails.
However, be aware that a significant sag will require a significant jacking of the frame rails, well past straight, just to get the frame to hold the new line you are looking for. I would suggest that all the body bolts be taken out to accommodate this.
Then you have the problem of actually seeing whether the rails are straight. It is difficult to get a line of sight or get a string line in place with the body still on the car.
You may find the rails tending to spread as a jacking load is applied. I have made two 'spreaders' of hardwood which are clamped between the rails with sash cramps to hold the rails in alignment as they are jacked. you could not do this with the body on.
I guess the bottom line is you will have a much easier time and achieve a more satisfactory job doing the straightening with the body off.
Hope this helps.
Allan from down under.
They nearly all sag behind the engine pan brackets. I would not attempt it with the body on. It would be nearly impossible to determine when it was straight. I would pull the engine too because you'll need to check the squareness by cross measuring the rails. And you don't want the rails to twist or spread with pan brackets attached.
I had already removed all but one of the cross braces before remembering to take a photo. You can see one toward the rear cross member. I think I had five or six bolted across the frame (top and bottom). The square tube I'm using under the jack is 2x2x1/4" that I happened to have for another project but I've also used a leg from my engine lift. It works if you don't have in-floor tie-downs.
I would run a string down the frame to determine the exact point of the deepest sag and the degree of the sag, then with logging chain, chain each end of the frame to the floor (you may need to pour you some recessed pad eyes in the concrete at the appropriate locations) and put a floor jack under the sagging portion and jack it up a little beyond the sag and let off then check the string, If there is still sag, I would jack it the amount I did before and a bit more, then check it again, I would do this until the sag was out. After the sag was out, to keep it from sagging again (steel has a memory) I would bolster the frame at that point, with a 1/2" x 2" x 24" long flatbar stiffener (assuming the inside web of the chassis channel between the legs is 2". Whatever it is, that should be the width of the flatbar stiffener) tightly inside the frame channel, bolted with 4 bolts on each side of the sag. If you wife hates the pad eyes, you can pour concrete in the recession and smooth over. Jim Patrick
Ken -- Putting those cross-ties on the frame while bending it is a good idea. I'll have to remember that.
Mike, the wooden spacers I mentioned do the same job as Ken's cross ties. I found when a real push is on to correct a significant sag, the rails tended to splay either way, top first or bottom first. This was when I had to push so hard that the tapered ends of the bottom rail were straight before the rail would hold a straight line on top when relaxed. The ramps need to be the old fashioned sliding jaw type with heavy threads. Newer pipe type clamps will not cut the mustard.
My set up is the reverse of Ken's. I straighten the rails by setting the frame up side down under a fixed beam in my garage. With the frame set on blocks, the porta-power is set up between the chassis rail and the beam above, and the push is downwards.
Just a different way to skin the same cat.
Allan from down under.
I use a length of railroad rail for my "beam, and put wooden spacers in the rail recess, both at the jacking point and the tie down points, so you are effectively pushing on both the bottom and top of the rail.
IMHO, a very slight bow upward is not a bad idea either! I said, very slight!
Question from someone who has never fooled with a sagging or out of square frame:
When you use a beam, jack, and chains as in Ken's photo do you just stress it cold or does a little heat help the steel "remember" where you want it?
Depending on just how bad it is, you can put shims between the body and frame and get things reasonably good. Just try not to lift the body so far that you make the steering shaft bind up, as it's connected to both the frame & the body.
Henry - There was a heated discussion about that a few years ago. (pun) One person in particular seemed to have convinced some that heat was the only way to straighten a frame without causing the frame to grow in length. Perhaps that may be but the amount of stretch was undetectable with a tape rule on the frames I've done.
The problem induced with heating a frame is that you can't heat enough of it (length) without a furnace to be useful. Spot heating the frame that is bowed will only cause the frame to take on a wave shape like that in the drawing below. A bow in the frame is caused by the entire length of the bow area to be flexed from it's normal. If the frame has a dent or bend, heat can be used on those specific locations to help reform the frame to it's channel design. It does not help for a bowed frame. In fact it makes it worse.
I use a process where I don't try and return the shape from a bow all at once. It is true the frame needs to over-flex but I do the jacking in stages with a "rest" period between increases in pressure. This helps to relieve the "memory" in the steel and spread the pressure over the entire bow.
Thanks, Ken. What you say makes sense.
Good picture and description of your frame straightening process, Ken. I learned quite a bit. .. thanks !!
Thanks George. I thought you were in the rust belt by now.