Supporting the body off the frame

Old June 14th, 2016, 01:51 PM
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Supporting the body off the frame

Is this sufficient for supporting my convertible body? Or should I move the rear support to the wheel wells or add support farther back in addition to what I have? I am a little concerned with the amount of weight in the back.

Does the bracing look good, 2 pieces of square tubing at door openings and one across the back side of the top two?

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Old June 14th, 2016, 02:16 PM
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When I did mine I ran the 4x4 under the rockers. I used a dado blade to cut a slot down the middle of the 4x4 then I put the pinch weld under the rocker in the slot. I didn't use any bracing either. What I did was removed the front clip and drive train but left the doors on. After I removed the frame and had the body supported by the 4x4's under the rockers I removed the doors. With no weight on the front end and the rockers supported I didn't have any flex in the body. I also supported the rear with jack stands and a 4x4 because I was afraid if somebody leaned on the trunk the car would tilt up in the front.
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Old June 14th, 2016, 03:46 PM
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Originally Posted by DewChugr View Post
Does the bracing look good, 2 pieces of square tubing at door openings and one across the back side of the top two?
A little late, isn't it?

Since you asked, the door bracing really isn't adequate. You want a triangle - one bar that goes straight back from the upper hinge point to the B-pillar, and one that runs from that point down and forward to the lower hinge point. This triangulation is dramatically stiffer. As you have it now, you simply have what is known as a four-bar-linkage - with emphasis on the word "linkage". Under load, it deflects to a parallelogram.



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Old June 15th, 2016, 09:58 AM
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I did my bracing a little different but I think you're on the right track. I used the front upper door hinge mount and the door striker as my bolted on mounts and then welded a diagonal bar to that brace and the pinch weld on the upper door. I think I'm also going to add a diagonal cross brace between the sides also. It might be over kill but I'd rather err on the side of caution. I personally I'm not a fan of cinder blocks though. I supported mine on floor jacks.
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Old June 16th, 2016, 06:27 PM
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take those blocks and chuck them down a bank...

They are never, ever, to be used to support any weight.

Hundreds if not thousands of guys have been killed by working on a car on cindar blocks.

and yes I know 2 guys can pick up an empty body shell
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Old June 17th, 2016, 01:48 AM
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I disagree with saying to not use the cinder blocks. They are actually concrete blocks and unless someone foolishly put them in other direction, they are very strong. Millions of houses are built on them. I disagree with using the dado blade to cut a slit for the rockers. That will weaken the 4x4.
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Old June 17th, 2016, 04:18 AM
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You can disagree, on using the blocks but you are very, very wrong. And telling others its ok is spreading dangerous lies.

You are also mostly wrong on cutting the 4x4, as a slit on the top may weaken it, but only very very slightly. When a simple beam is loaded in the middle, and supported on the ends, the top is in compression, and the bottom is in tension. If you cut a slit on the bottom edge, it would weaken it significantly, but on the top its negligible (assuming you don't go crazy and cut three quarters of the way through).

Last edited by Krom; June 17th, 2016 at 04:30 AM.
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Old June 17th, 2016, 06:08 AM
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I used cinder blocks or wood blocking with single 4x4's across front and back and never braced the doors. Four people can easily pick up a stripped tub. As long as your rockers are solid (and most are because they were galvanized) a convertible body has zero deflection when sitting in a static condition. Even with my fat a$$ inside there was no body flex. I'll note that the floors were replaced before I started. If I had to completely strip out floors I would have braced the doors.

The pic below shows three 4x4's across. I usually only had two (under the cowl and at the rear of the trunk). The side to side stability isn't ideal with single cinder blocks as shown below. If you double them up and alternate the direction by layer they won't go anywhere

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Old June 17th, 2016, 06:22 AM
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Originally Posted by Krom View Post
You can disagree, on using the blocks but you are very, very wrong. And telling others its ok is spreading dangerous lies.

You are also mostly wrong on cutting the 4x4, as a slit on the top may weaken it, but only very very slightly. When a simple beam is loaded in the middle, and supported on the ends, the top is in compression, and the bottom is in tension. If you cut a slit on the bottom edge, it would weaken it significantly, but on the top its negligible (assuming you don't go crazy and cut three quarters of the way through).
You're wrong on the cinder blocks

Cinder blocks can support tens of thousands of lbs in compression. The only issue is stability

You're also wrong on cutting 4x4's

You reduce the cross sectional area of a 4x4 the same amount whether you cut it on the top or the bottom. By cutting on the bottom you subject the member to shear parallel with the grain which certainly lends itself to a quicker, more catastrophic failure, but I wouldn't notch a 10'-12' 4x4 on either side that was supporting the body. A 4x4 is just barely adequate to support the body. I used them too, but if I had 6x6's I would have used them. Pressure treated lumber just sucks in general. It's strong but very stiff. Consequently it doesn't flex much before it fails

and yes.....I am a licensed structural Engineer
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Old June 18th, 2016, 03:06 AM
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And I would use more than a Single 4x4 on each mount. Use 6x6 or put two 4x4s next to each other on each set of blocks.
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Old June 18th, 2016, 09:25 AM
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Guess a licensed structural beats bsme.

But I will refuse to agree with you on cmu. They are dangerous, and fail catastrophically when they fail. Lots of people have been killed by collapsing cmu dropping cars on them.

FWIW you can easily support an empty body with 2 2X6s running the weak way, and I'd be confident doing it with 2X4s, but I had the 6s laying around.

Hell you can even support one with under $10 of harbor freight ratchet straps, ($9.95 for 4, but I always use the 20% coupon lol) but I wouldn't recommend it
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Old June 18th, 2016, 10:32 AM
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Originally Posted by Krom View Post
But I will refuse to agree with you on cmu. They are dangerous, and fail catastrophically when they fail. Lots of people have been killed by collapsing cmu dropping cars on them.

One evenly loaded 8x15 CMU block will theoretically hold about 75,000 lbs


Area of the block (about 50 sq in) x 1500 lb/sq in strength concrete.


Now this isn't completely true because you can't evenly distribute the load and the edge distance will reduce the capacity as well but you get the idea. 99% of the time that CMU blocks fail in compression it's because someone point loads them. Some state building codes don't even allow you to use them for full foundations. They are terrible in tension (as in a side loaded foundation) even if you put rebar in them and fill every other void with concrete (which is what most states require when you use them in a foundation wall). I wouldn't build a doghouse with them but I would use them to support my car. A simple way to ensure they are loaded evenly is to place a piece of plywood between each layer. This gives you the same effect as placing a layer of mortar between each course.
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Old June 18th, 2016, 11:28 AM
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right until a bar or the jack handle falls against one, and it shatters.

Or until you are trying to lower it, and the jack drops all at once, instead of going slowly as you planned, and it shatters.

Or something hangs up, and instead of lifting the entire side, you lift one corner, transferring all the weight onto one stack of blocks, at an angle, and it shatters.

There are a million good reasons to avoid blocks, and not one single good reason to use them.
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Old June 18th, 2016, 11:32 AM
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Old June 19th, 2016, 01:35 AM
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Now you're making the choice tough. A US made concrete block or harbor freight metal (not sure if it is actually steel) Chinese jack stands. Just kidding, but not sure I would crawl under a car supported by anything from harbor freight. They are fine for buying cheap throwaway screwdrivers, sanding disks, and work gloves , though.
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Old July 3rd, 2016, 06:22 PM
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Just got done pulling. The convertible body off the frame, going to sand blast the frame paint it and install all new lines and brakes
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Old July 4th, 2016, 06:58 PM
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RR48, the pulling is not done yet. With those blocks stacked that (the wrong) way, somebody's going to be pulling you out from under that mess. What if it rolls over and destroys your house?
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Old August 28th, 2016, 07:20 AM
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and here I thought that using 4 straps was sketchy lol
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Old August 31st, 2016, 06:35 PM
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Frame cleaned and painted, taking a break till it cools off then jump back on this
Going to replace all the lines next
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Old September 1st, 2016, 06:28 AM
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I have to agree on the stack of cinder block picture . That looks a bit dangerous , and danger is my middle name . Just be careful is all I'm saying .
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Old September 1st, 2016, 07:07 AM
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Got the body sitting on the trailer, no problems. This will more than likely be my last time I will do a job like this again, getting to old for this stuff
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