C2 66 Birdcage Rocker Channel Rust - CorvetteForum - Chevrolet Corvette Forum Discussion

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[C2] 66 Birdcage Rocker Channel Rust

Old 12-05-2018, 01:12 AM
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RLMeyers
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Default 66 Birdcage Rocker Channel Rust

I am in the process of restoring my Northeast convertible and in need of sage advice from forum members who have dealt with corroded bird cage issues. The bird cage appears to be in good shape in the areas of the #1, #2, #3 body mounts, front and rear door pillars, and windshield mount area. However, the undersides of the rocker channels on both sides have serious rust and I suspect their strength is compromised, although there are no signs of cracks or distress in the fiberglass bonded to the channels. Is it possible (or advisable) to attempt replacement, repair, or reinforcement of the rocker channels with the chassis removed and the body suspended/supported? My original plan was to clean up the rust on the underside of the channels, prep them with zinc phosphate solution, and coat them with POR-15. Now that the chassis is removed and restored, I am able to examine the rocker channels more closely and I am concerned about how much strength remains and how much is required. It would seem to me that rigidity provided by solid body mounts to the frame and connections to the front and rear pillars would reduce the risk from weakened rocker channels. I would appreciate recommendations from anyone with experience/scar tissue gained from wrestling with a similar situation.

Thanks in advance,
Bob
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Old 12-05-2018, 08:22 AM
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Have you probed the rocker channel with a screwdriver or pick to see if there are any places rusted completely through? That rocker channel is pretty critical on a convertible - not much else of structural capacity holding the front and rear sections of the body together. And pretty near impossible to work or weld on without removing a good deal of fiberglass first.
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Old 12-05-2018, 08:59 AM
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There is a sleeve that's been produced to line the old channel if you don't want to get into replacement of the rusted ones. I would guess they are still available somewhere.

https://www.zip-corvette.com/63-67-r...el-sleeve.html

Not sure of the recommended installation procedure - maybe sandblast existing rocker, epoxy primer and then structural epoxy adhesive and clamps.

Last edited by DansYellow66; 12-05-2018 at 09:00 AM.
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Old 12-05-2018, 03:27 PM
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Thanks DansYellow66

I can see that the passenger side rocker channel has rusted completely through on the inboard side of the channel about one foot back from the front. There is an irregular hole about 1/2" by 1/4". A few other spots don't seem to have much rust at all. I have not found any other voids by poking, but I have an idea that I won't like what I see when I get finished grinding or sandblasting off all the rust. There are small circular holes a little smaller than a dime in the outboard sides of each channel that look like they are part of the original configuration. The thickness of the channel at the edge of these holes is the same as unrusted parts of the channel. My hope is that there is enough sound material left that the sleeves you mentioned might be spot welded in sound places to restore the birdcage's structural integrity. I guess I'll have to see what I have left to work with when the rust is gone or reduced to the point that I can tell what steel is left. I have a friend who was an NCRS judge who suggested welding steel strapping 1/8" thick by 3" wide or so on both sides of the channel, but the sleeves sound like the best approach. I wasn't aware that they were available.

This might be rationalizing, but from a design perspective, I would think that if the convertible body has solid support at each of the 10 body mounts, and the frame was sound, there should be very little birdcage flexure in the roll, pitch, or yaw axes even if the rocker channel was weak. Where I think there might be problem, is from the weight and shock load of seats and passengers focused right at the middle of the channel. Reduced strength there might result in fiberglass stress and cracking of the floor and sides near the doors. When I get through with this project, I doubt the car will experience much stress from my driving (g forces, cold or rain for that matter). But I don't want to ignore possible safety concerns either. What do you think?

Thanks again for the response - if any other thoughts come to mind, please post them. I'm probably going to be at this a bit longer than I thought.

Bob
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Old 12-05-2018, 04:24 PM
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That one small hole is sort of puzzling and may be something unusual. Is it at the top of the channel or actually down on the inside wall? If the channels are solid back at the #3 mount behind the seat that single hole may not be of much consequence. You may just need to repair a hole and clean up and prime the metal. If you do try the sleeve and if you have undercar exhausts with the rocker panel brackets on your car, that may make use of the sleeve a lot more difficult. They may have to be removed the sleeve cut to fit around them - not sure what the recommendations are for that.
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Old 12-06-2018, 01:07 PM
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I have attached (I hope) 2 photos of my problem rocker channels. The first is a front to back view of the driver's side channel. Damage to the brackets is clearly visible in addition to the channel scaling. The second is of the passenger's side and shows the irregular hole in the channel side wall. Next step is to try removing as much scale as possible with a pneumatic scaler and see what metal is left. I did a consult with a local auto machinist/welder (does dragster frames, etc.) and showed him the photos. He seems optimistic that there is enough strength left for my purposes if I remove the scale, prep them, and coat/seal them. That will have to be confirmed in person once the scale is removed.
Bob
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Old 12-06-2018, 01:14 PM
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Missing photos

Left rocker channel front to back

Right Hand channel with sidewall hole
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Old 12-06-2018, 02:18 PM
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It is pretty scaly. Some pieces of the rocker panel brackets are gone. I think you are probably right in cleaning it to bare metal before evaluating what to do next.
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Old 12-06-2018, 04:13 PM
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There is only one true way to fix and that is to remove and replace with a new channel. I have not done it myself but I would think there would be people on here that have and would know how involved it would be. I think you already know that.
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Old 12-07-2018, 10:42 PM
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Thanks, Moxie62 - I appreciate where you are coming from, but after reading in the forum what Tom Sammut did to rebuild a severely rusted birdcage, I am convinced that such a repair is way beyond my talent and resource level. You may want to find ricks327 post (search "birdcage corrosion"). From the AIM, exposing and replicating all the welds on a new channel and associated brackets and pillars to make it as close as possible to "as built" would be the true way, but since I don't plan on competing the car, that alternative is too idealistic for me, given what the time and cost would be. I appreciate your comments, though. I'll post progress as I find out more.

Bob
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Old 12-07-2018, 11:02 PM
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From discussions with a Paragon tech, the brackets don't contact the frame when the body is remounted. It seems to me that if the only function they serve is to hold up the rocker panel trim, I should be able to remove all the corroded ones to install the sleeve (if that is what I have to do) and then reinstall 3 or 4 of them instead of all 6. For that matter, I could just cut off the horizontal parts of all the brackets and leave the healthy vertical parts there to mount the trim to. If I have to replace them, positioning new ones to line up with the trim mounting holes might be tricky, but I'll cross that bridge after the plan is better defined.
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Old 12-07-2018, 11:09 PM
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The trim actually screws into the bottom horizontal pieces, however mine was solidly held in place by three plus the two end screws. Your plan should work.
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Old 12-08-2018, 01:05 AM
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Thanks Factoid - I think I was unclear when I spoke of the "horizontal" part of the rocker panel support bracket. The part of the bracket I was concerned with is the top part that spans the rocker channel and is tack welded on each side. The rocker molding itself hangs from the rocker molding retainer and as you mentioned, is fixed at the bottom with screws into a nylon captive nut mounted in the short lower horizontal part of the bracket. If I have to use the rocker channel sleeve, I would have to cut off all of the top horizontal parts of the brackets that span the rocker channel before I could position the sleeve in place. How it would be retained in place (welded, epoxied, or screwed) I have yet to learn. Hoping to hear recommendations from tech guys at zip-corvette tomorrow. I also have to assess the health of the rocker channels by removing the rust/scale to figure how much "broke" I have to fix.

Bob
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Old 12-08-2018, 09:06 AM
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Bob, I knew what you meant, I was too brief in my answer. I think you can drill the spot welds and remove the brackets. Then remove as much of the surface rust and scale as possible. Treat the rust with either POR15 or Eastwood. Use two coats and let the last one dry for several days. Hopefully, Zip will give you the best method for welding in the new sleeve. Then pick the best three brackets, cut off the top horizontal and spot weld them in place. They will be plenty strong for the purpose. I just removed my rocker trim and the top channel that it hangs from holds it pretty tightly. Good luck!
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Old 12-08-2018, 09:48 AM
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I forgot the brackets aren't up tight against the top of the birdcage channel - my car is an original side pipe car and doesn't have them.
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Old 12-08-2018, 02:06 PM
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Bob, as bad as your trim brackets are rusted (and the rusted through area on the inside edge of the channel) I would be very suspect of the condition of the rest of your birdcage rocker channels. Granted the rocker trim brackets are not structural, but they also aren't typically rusted through like yours are ...unless they've been exposed to some manner of extreme moisture. I frankly have difficulty imagining how they could get in this condition without severe rust in the rest of the channel or even the frame.

Here is what a more typical set of 50 year old rocker trim brackets should look like... (these are on a '63)


In any case my recommendation would be to take the body to a qualified repair facility and have just the channels replaced with new ones (assuming the uprights of the birdcage are themselves solid) if you don't feel comfortable doing the repair yourself. You may even find a good fabricator that will come to your garage and replace the channel right there. It shouldn't require a lot of sophisticated equipment to perform this task. Just a capable welder with a good welding machine.

Like you I did not feel qualified to take this job on, so I had a highly recommended shop replace the lower channels on the birdcage in my '73 convertible.

Good luck... GUSTO

Last edited by GUSTO14; 12-08-2018 at 02:06 PM.
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