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Old 03-11-2013, 03:38 PM   #1
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Rear Hold down plate replacement

I am putting my '73 Globetrotter back together after a shell off, and am replacing the back panel, as it was disintegrating where it was in contact with the steel hold-down plate. This plate is also heavily rusted and corroded, and I'm thinking it ought to be replaced as well. I could start with a piece of flat stock and try to fold it, but getting an even fold in a piece that is 45 inches long would be pretty hard without some massive equipment. I could get two pieces of bar stock and weld them at the proper angle, but I question how robust this design would be.

Also, if I end up making one from scratch, are there any arguments against making it much taller, and doing a double row of rivets, like in the front?

I've looked around at some of the online parts dealers, but haven't found a replacement.

Any suggestions?
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Old 03-11-2013, 06:18 PM   #2
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I chose to reuse after a total cleaning and extreme POR-15 for three coats.

The double row of rivets up front is insurance against shear effects from tow-vehicle suspension shock transmitted through the hitch - there is no such stress on the back. I did add to the rivet count but not doing separate double rows...

On mine the interface surface to the aluminum was not horrible, the floor contact area had most of the pitting. Using stainless steel washers the clamp-through-the-floor into the iron crossbar is every bit as strong as factory - if yours has perforations or major missing metal it might be a candidate for replacing but general pitting doesn't condemn it in my book.

Edit - http://www.airforums.com/forums/f36/...ml#post1211463 shows the process..
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Old 03-12-2013, 09:10 AM   #3
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Properly welded, a welded plate would be just as strong and robust as the bent plate, in my experience anyway.
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Old 03-12-2013, 10:19 AM   #4
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I'm right behind you Belegedhel!!! I think I'm following in your footsteps. I've already copied your gantry design and pulled my shell. I just had my frame metal fixed up, and about to go to powder coat (or por15 if powdercoater is too far backlogged.) I've read pros & cons to PC vs POR, but for $500 to sandblast and PC, I cant hardly turn that down! My only issue is that I've still got lots of holes to drill in the new steel and POR is easy to touch up, where PCoat is breached....

My frame needed 12 outriggers, including a new one for step and I replaced all wheel well outriggers, rear most crossmember and some z bar to fabricate new mounting designs for all the tanks. I'm doing the early 70's design with the z bar that holds up the 1" plywood and I've done it with the black and gray too, so I can service either one without having to pull the entire rear pan. Not my favorite, but was the solution I came up with since both of the galvanized pans that formerly held them up were completely rusted.

When I was having the metal shop fabricate all my replacement pieces, I had him bend me a piece of Aluminum for my rear hold down. I did 2" x 2" in approx 8 gauge which is around 1/8" and I went 42" long. I saw somewhere that its about 100 degree bend, which is what I had him do, but I have since seen somewhere else that it is actually 107 degrees so I dont know which is right and wont know for a couple weeks yet.

I've been re-thinking if I should use something stronger than Aluminum?? I originally thought I wanted to avoid dissimilar metal issues, but now wondering if I should have done SS or even go back to steel. Although, the entire C-channel is aluminum and it is essentially a hold down plate, so maybe I'll be fine????

Looking forward to hearing what you decide and if anyone has any input on my Aluminum idea.
Micky
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Old 03-13-2013, 02:05 PM   #5
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Hmmm. I've been thinking more on this topic, and figure that the old plate is still serviceable, although heavily corroded and deeply pitted. Still, I figure the pitted steel is stronger than the aluminum sheet it will be riveted to. One thing that worries me is that the holes through which the hold-down plate is bolted to the rear cross member are sooooo close to the edge of the plate, and sooooo far from the bend (see the attached pics for images of the corrosion and the location of the holes--the plate is oriented with the bolted down part sticking up in the air).

Does anyone else's plate look like mine?
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Old 03-13-2013, 02:37 PM   #6
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Yours looks brand new compared to mine.
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Old 03-13-2013, 03:02 PM   #7
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Landing the shell... remember to 'stretch' the shell lengthwise to keep the fender flaps, battery and water heater openings taut and even. Where the bolt lugs were and where they can/will wind up is fluid.

I see the edge holes for the tie-plate, but where did they correspond on the frame end cross piece?

The aft tie-plate may just be stiffener & the real strength 'to hold the frame up' is transferred through the two rear ribs & doubled sheet seam picking up the ladder frame at the C-channel bolts. Remember to oversize washer or plate the C-channel bolts, there is a mod to add angle iron ears to the frame under the floor to broaden the load attach points.
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Old 03-13-2013, 03:49 PM   #8
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My rear most cross member had mostly rusted away, so was replaced. Thus, I don't know where the bolts in the tie-down plate hit the cross member, but I would guess they were fairly centered, as that cross-piece wasn't very wide.

The shell is back on the frame. I knew that I was going to replace the back panel, so decided to do that after the shell was back in place so that I wouldn't run the risk of damaging a newly replaced panel during the reinstall.

As I think more on this topic, I begin to wonder if the rear tie-down plate isn't a combination of overkill and an Achillies' heel. I know I had rear-end separation, and that can be blamed on the rotting floor at the tail of the trailer. Once the wood was rotted away, the tie-down plate made no difference as it was floating as much as the C-channel. But, the iron-to-aluminum electrolysis definitely ate away at the aluminum skin. I wonder now whether I should modify the rear-most piece of plywood subfloor so that there is room for a rigid (steel) spacer so that the rear hold-down plate clamps directly to the rear cross member. That way, if the plywood gets squishy again, at least the connection of shell to frame should be solid.
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Old 03-13-2013, 04:21 PM   #9
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You mean like Wabbiteer in post #59 here
http://www.airforums.com/forums/f36/...ml#post1211463
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Old 03-14-2013, 08:49 AM   #10
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Precisely--I guess there are no new ideas!
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Old 03-15-2013, 09:15 PM   #11
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Thought you'd get a kick outta this....
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Old 03-15-2013, 09:50 PM   #12
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Mine looked like Mixters. I used a peice of aluminum angle to replace, while the angle was thicker it didnt create any issues reattaching the shell. My goal was to get rid of the corrision issues between the two metals.
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Old 03-15-2013, 09:55 PM   #13
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Did you use just 90 degree angle? 2"x2"? I had a 4" piece bent to 100 degrees creating 2"x2".... havent tested yet. I have the same concerns with dissimilar metal issues, but been wondering if the 1/8" thick material would cause any issues, if the angle is right, and if aluminum is strong enough to function as a "hold down" plate.

Good to hear it worked out!
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Old 03-17-2013, 02:07 AM   #14
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Please let us know if the 100 degrees did the trick. I need to do the same thing ASAP.

Thanks

Tony
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