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Discussion Starter · #1 ·
I have rust through on the first 12 inches of the rear frame rails next to the front leaf spring bolts. I am trying to decide whether to repair or replace. I believe that replacing the whole rail is very difficult without damaging the trunk. My trunk floor is in very good shape and I do not want to compromise or replace it. The rails are solid except that the bottom has rusted through. The sides are still in good shape. Maybe a new piece of formed steel could be welded over the top? Also would welding in a subframe connector help to solidify the whole body and minimize the stress on the rusted area?

Any thoughts would be appreciated...

JB Mitchell
 

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You can purchase partial frame sections. That said, I would just replace the entire rail. They rust from the inside out. It is much worse than it looks I assure you. Might want to look very closely at the other side too. If the trunk is a worry, grind the spot welds instead of drilling them. That's how I save some parts. Good luck. I replaced my frame rails with full length Dynacorn. They were thicker than my originals, maybe so they could be used on convertibles' too?
 

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Discussion Starter · #3 ·
Keith - thanks much. I must admit that I am very green when it comes to chassis work. Where would you grind the spot welds vs drill them? If they are attached to the trunk floor dont you have to make holes in the trunk floor either way? I am actually at a stuck point trying to figure out how to even start getting them loose - they seem totally integrated into the floor. Is there something that you can do from underneath the car? :(
JB
 

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Spot welds are a tricky deal. It takes some practice but you can grind them away very carefully with a cut-off wheel. Take your standard cut off wheel tool, and stack about 2 or even 3 together. Make sure you keep them centered on the tool. Then locate your spot weld, and take your time. You can safely grind them off this way. You will want to do this from the bottom of the car, so you don't damage the trunk floor. Remember you can remove the weld from either side as it is a pinched weld, depending on which piece you are trying to save. The reason for the multiple wheels is to keep your cut the same across the weld, and its harder to cut through with more wheels, since we are trying to grind. I do it with 1 wheel, but i do this everyday, and have had a lot of practice. More wheels will take a little longer but it helps when you are new to it. It takes some time doing it like this, but effective. If you want to save some time, get yourself a spot weld bit. Not the type with an arbor sticking out of it. Don't try to cut all the way through, just use to mark and mildly cut. Get about half way through, and cut off wheel the rest of the way. Be careful and pay attention to how deep you are going.

About why you should replace the full frame rail. Its a matter of preference/safety in my opinion. Remember that in structural integrity, something is only as strong as the weakest link. You may have more time wrapped up in replacing the hole thing, but you will know that it is straight and strong. We can get you all the frame dimensions as well in the event that you do decide to replace the entire thing.

Sub-frame connectors will strengthen the car, you are tying the front and rear together. Although i am not a fan of bolt ins, i always weld mine in. That makes it a pain in the butt, if you ever have to drop the frame, you will be cutting them off. That being said, i install them on everyone i build that uses a factory sub-frame. Since you said that the frame rails are rotten, make sure to check the front leaf spring mounting location for rot. You wouldn't want a leaf spring coming through the floor the first time you romp on it. I have seen it happen.

I have attached a video demonstrating basic cut-off wheel removal of spot welds.

 

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I patched the right rear frame rail on mine from the axle back. I wouldn't do it again but I'm not doing it over either.

I'm a fan of the hole saw "holesaw". It takes finesse and the welds are not always the same diameter as the cutter. I sometimes drill an 1/8" hole thru both pieces to keep it from drifting. I find slow and steady works best and keeps breakage to a minimum.

Jeff
 

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I couldn't believe how flimsy the stock frame rail are! The replacements are strong!!!! I replaced both but this was with the new trunk pan out of the car and easy access. You MUST have a way to put these back accurately if you decide to replace.
That old saying "If I can do it you can?" I had a couple years practice with spot welds and welding before i made it back to the rails. It wasn't really any more difficult than any panel replacement or patching by that time. If you have faith in your welding then locating spot welds and cutting them is just a matter of patience and practice.
Basically it boils down to cut the spots, clamp in place, and weld it up but there is a lot of thought that has to go into it. And please make SURE you have a way to realign. I got mine off a quarter inch and I think that was about the limit before it became critical to the way the car tracked.Good luck, do a lot of searching on frame rails and you will see if it is a job you wish to tackle.
 

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x2. Not the easiest thing to start with. Locating and alignment can make or break a car. Dont want the thing to run like a dog up the road.
 

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Discussion Starter · #8 · (Edited)
Guys - you are the best:hurray: - thank you so much for all the replies. I am brand-new to this forum and didn't know what to expect. I am really happy to see all the great help that people are offering. I haven't rebuilt a car for 30 years and this is the first time I've done it without a sidekick to bounce ideas off of.

I've been doing A lot of investigation into my frame rails because of what I've learned from your responses. What I found is that only the first 8-10 inches of the frame beginning at the front spring mount are rusted. Once the frame begins to curve upward it is like a rock - really solid. It must be just like my floor pan rusting out. I had the car parked for 27 years in a shed with gravel floor. Anything on the car within a foot of the gravel, ended up rusting. Otherwise every other part of the car is fine.

I found a posting where a guy removed his floor pan, then he took his torque boxes out. Then he welded in a new floor (do some floors come with new torque boxes attached?) Anyway this left the frame wide open. My torque boxes and spring mounts are good. I am thinking that I could easily repair my frame with the torque boxes out of the way if I do the same when I replace my floor pan. What do you think?
JB Mitchell
 
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