Rear subframe rail rust, mouse nests

[Dunk67]

'66 with rot on the driver side rear subframe rail, holes to poke through the pick mouse nests out of. The passenger side rear subframe rail is not soft or cumbly, but reaching inside the factory holes in the side is full of mouse nest. That would surely rot it out if it gets wet and holds moisture.

Are repop rear subframe rails available for these cars? I'm guessing not. If that's the case I can patch the worse one and treat the bad one that still seems solid enough. Anyone know what gauge metal the subframe rails are?

How to clean the mouse nests out of the intact and fairly solid subframe rail? I'm thinking cut holes with a hole saw as large as I can as needed and weld in patches after cleaned and treated inside? After welding, spray rust encapsulator inside and out again to cover weld beads.

[Rt.146]

If the car is found structural sound, I would then strip the body of all sprung an un-sprung weight and the interior, put it on a a rotisserie where you can exam and possibly fix it for the better.

[jtschug]

I'm a totally amateur welder, so please don't roast me too hard.

There is no rust anywhere else on this car, but there were two holes about the size of a 50 cent coin at the bottom of each subframe. I also wanted something solid to weld the rear sway bar bracket to, so I added this metal in this area.

I did this in two pieces: 1st used a shrinker/stretcher to form a piece that covered the curved weld flange and the bottom side of the subframe. Then I bent a plate to cover the inside surface of the subframe and welded those to pieces together and a few plug points, and also around the edges.

I forget the gauge I used, but it was two sizes thicker than the shrinker/stretcher and the sheetmetal break was supposed to handle. It was a real pain but it turned out alright.

[Dunk67]

Unfortunately I don't have the space for a rotisserie and that level of restoration. The car is not structurally sound of course, given the subframe rail rust along with all the trunk rust since that ties it all together in the rear. Sure I could just send it to the scrap yard and every other '64-'66 goes up a wee bit in value from fewer on the road or available, but I don't think this one is too far gone. Pretty typical level of rust for the mid-Atlantic, mostly areas where premade panels are available.

In any event, given the trunk rust the best access to this mouse nest infested frame rail seems to be from above. Removing the common rust area trunk panels will give me access to the inside of the frame rails to clean, treat, and coat.

I've done some patching and welding over the year but nothing on this level. These old cars aren't getting any less rusty as time goes on so I may as well dive in. I ordered a full set of new trunk metal (https://www.classicsheetmetal.com/ecomm ... 64-66.html). I'll have to fabricobble a few bits for what the panels don't cover. I'm reasonably confident I can make a structurally sound repair.

I found a super helpful video on replacing the trunk panels in a '64-66 https://youtu.be/6eyPefXgzkM), knowing what to expect makes it less intimidating. One thing not addressed in that video is how to support the car to be sure it stays straight. It looks like that guy just had it sitting on the ground. This concerns me when cutting the whole trunk out, including the trunk floor panels that are welded to the top of the rear subframe rails. Am I okay to leave the car on the ground sitting on the rear axle or should I jack up the rear and support it forward of where I cut metal out? If so that may be challenginggiven the shape of the frame rails over the axle, unless i support it well forward of where I will be cutting out metal. For the rotted frame rail, I'm guessing repairing the rotted portion before cutting out the trunk might help keep the car dimensionally stable and would be prudent to do first?

[jtschug]

The way I did it was to support the back end of the car where the big bumper brackets attach to the rear subframe.

I had the leaf springs, rear axle and driveshaft out of the car, I put a large 6x4 timber across the width of the car and then braced it up to the rocker panels on each side. Then I used two bottle jacks on each side lift that center section of the car up evenly.

The place to watch is the gap between the rear edge of the door and the quarter panel, this should be absolutely parallel, no A gap or V gap. Use the bottle jacks to lift and drop the timber to get that gap on either side correct. Once it was close, I opened and closed the doors a few times making sure they didn't sag or change the gap when they were open. Once I was sure everything was in the right place, I put jack stands under the timber to support it (because bottle jacks drift over time) and used shim shingles to support the weight without letting it sag at all. Then I removed the bottle jacks and rechecked to make sure nothing settled. Now you can cut and weld and keep everything straight. Try not to remove anything more than you have to at one time.

If you've got a whole body shop this can be done more accurately in a big rack, but if you are doing this in your garage, like I was, this was how I attempted to weld on things without twisting up the body. The structure of the car flows from the rocker beams, through the torque boxes to the rear subframe, so by supporting the front of the car and the back of the car and adjusting the support in the middle of the car it is possible to adjust things and eliminate sag.

[Dunk67]

Perhaps to the dismay of purists I haven't scrapped the car and am diving in and hoping for the best. The car is currently sitting on jack stands under the axle. I put two pieces of masking tape across each door at the rear gap, to gauge if anything is moving. Tape still lines up and doors open and close normally. I think it'll be dimensionally stable only doing one side at a time.

Something of an unknown is the inner quarter panel pieces which are available repop are rotted toward the front. Lower rear quarters were quick and dirty by PO, pop riveted just below the body line right over original metal, none of which was removed, and self tapppers in the bottom.I'd like to replace the inner quarters while the trunk is apart, for easier access, but may create a can of worms with outer quarters and I don't want to get too far into cosmetic body work that someone else will be doing finish work over. I suppose on one hand I could do it all myself but I'm trying to avoid that. My other thought is just leave the rotted inner quarters and put a few self tappers through the flange and let the body shop doing finish work deal with them.

Everything is a bit worse than I expected, as is to be expected. I turned up other hacks from PO, fiberglass and bondo in various spots that were basically gone and clearly the poorly sealed, held water and accelerated the rot.

Either way, mouse nest resolved. The spot this nest was is exactly where the other frame rail rotted. Surely the same issue that held moisture. This side is remarkably solid though. In any event, is soaks in Ospho tonight and everywhere I don't need to weld will get Eastwood rust encapsulator or frame coating before being buttoned up.

[Rt.146]

Jamiesons is working on a 66 Convertible with rust problems like you are describing, he does, painstakingly, describe how he will repair what he is working on. https://www.youtube.com/c/JamiesonsRepairShop100

[Dunk67]

Thanks, another good resource for metal repairs and particularly helpful to see it on the same car I'm working on.

[Dunk67]

Progress... Wheel house and the two pieces that join it are patched at the top. On to patch the lower parts of these, then the rear bit behind the tail light, the lower edge of the piece behind the gas tank, and figure out what to do about the inner quarter panel. I have no idea what I'm doing, but I guess it's better than it was which will have to be good enough.

[Dunk67]

Another piece cut, fit, and prepped for the inner panel. For the outer panel I made a flange for plug welds to the inner panel and welded that on. Another coat of Ospho inside the frame rail and farther up over the hump since I have more access now. This stuff is tedious. Probably weld in the rest of this section tomorrow, and ponder what hole to plug next.

[Dunk67]

I dug up a small wire wheel that fits inside the frame rail and went at the rusty bottom, poking two holes where the mouse nest was. Remaining metal doesn't break apart but is obviously thin near the holes and you can see the pitting and rust scale flaking off the bottom. The bottom is thick and solid behind the bumper mount braces and a few inches forward where the rail curves upward toward the axle.

I'm thinking I should patch this section but not sure the best way to go about it. The subframe is made from two stamped pieces that have a lip at the bottom that is spot welded together. The outer section is 16 gauge, the inner is 18 gauge. The bend into the flange at the bottom where they are spot welded holds water and contributes to rust.

I'm pondering a few ways to repair this. The quick and dirty would be to bend an L shape into some 16ga to fit inside the frame rail and weld it in past the thin section, leaving the existing metal in place. Cleaned to bare metal, weld through primer, rust encapsulator on everything.

The more labor intensive would be to support the car forward of the axle, cut out the thin metal, make new parts the same shape as existing with plug welds on a lower seam, weld it in, and maybe for good measure plate the inside of the frame rail on the sides with a longer pieces of 16ga.

Another options is simply making a U shaped 16ga patch to weld in place of the thin section. This approach would eliminate the seam at the bottom of the frame rail that collects water, and would be easier to make. I could drill a hole or two in the center near the lowest point to ensure good drainage.

Interesting to note is there is a very thick piece of metal around the access hole on the inside of the frame rail. I'm guessing this was intended for tying the car down during transport or towing, to keep the 18ga inner subframe from tearing. It's not really long enough to add any rigidity to the structure. I could duplicate this hole and reuse the inner brace

I'm sure there are other ways to patch rear subframe rails as well. I'm open to any options or suggestions.

[Dunk67]

I was pondering this morning and I think I've decided to make the patches to be very similar to original, original shape with the plug welds on the bottom flange. This will allow me to cut out only one side of the frame rail at a time, weld in the side and bottom, repeat on the other side, then plug weld on the bottom. With the car supported by solid sections of the frame forward of the trunk this should minimize any flex when I cut the thin metal out. At least that's how I envision it.

The seam as the bottom of the frame rail shouldn't be a big deal, my rust treatment and coating will likely be better than what the factory did inside the frame rails and this car will only see occasional rain when done rather than snow and salt as it has since new.

[jtschug]

This is a whole invisible part of the car, so I welded the strengthening plates on top of the existing metal to avoid any distortion that might happen when cutting out the old metal.

You are absolutely on the right track with Ospho or other phosphoric acid treatment to neutralize the rust. I also used a "cold galvanizing" weld-through primer on the back side of the new plate and on the metal being covered up to prevent rust from growing in between the two layers of metal.

After all the welding I put a good quality rust resistant paint on everything and then applied seam sealer all around the patch to keep water from getting in between the two layers. The last step after everything was done is cover the whole underside with pickup truck spray on bed liner. After it goes on it looks identical to the original rust proof / sound insulation that was on the underside from the factory, but it is very tough and durable.

[dgalietti]

Your trunk looks very similar to how mine was. Except my lower pan was half gone and I had no frame rail issues.

Have you looked at classic sheetmetal? They usually have good sales on these parts and they ship fairly fast.

I ordered everything that they make for the trunk and it covers 95% of what you are doing.

[Dunk67]

I picked up some Rustoleum spray bottle of rust converter gel. It's phosphoric acid, so probably about the same as Ospho but with a thickening agent. It seems to be working nicely inside the frame rails and on the vertical surfaces.

I have all new trunk pieces and trunk seal pieces from Classic Sheetmetal, along with the inner and outer lower quarters. Test fitting they seem like good quality reasonably accurate pieces so far. Would be nice if the trunk side panels extended farther forward, or the outer trunk panels had a flange at the rear. Beggars can't be choosers though and those pieces seem easy enough to make.

I started on the passenger frame rail today, cutting out the bad metal. I would have liked to go a little farther back but I don't want to mess with the spring hangar on this side. Trying to bend up a new 16ga patch in the vise resulted in cracking the new metal. Not sure if it's too thick to bend without heat, or I was trying to make too sharp on a bend with the hard 90* in the vise jaws. I ordered a press brake insert for the vise. It will probably work for 16ga if I put a little heat into the new metal first. A little delay but should be easier and more accurate than beating on 16ga.

I took a couple quick measurements of the frame rail before cutting, height off the floor and side to side. No movement that I can tell with a tape measure. Very little weight in this area and weight is off the axle.

Any tips of bending 16ga? this side of the frame isn't too bad but needs patching, I'll have more to patch on the other side. It's considering a HF brake that claims to be good up to 16ga, maybe a bit flexy at that size but there are writeups for how to improve it. Other possibilities include angle iron or wood along with heat, hammers, an/or a press.

While I wait for the vise brake I'll get to patching some more of the thinner sections, maybe the inner trunk piece behind the tail light or the bit behind the gas tank that the trunk floor attaches to.