Well I jacked it up like that, welded the brace in the door frame, took some measurements, and the replaced the rocker. And the door frame geometry didn't move at all. I'm going to test fit the door today. With 1/4" factory tolerance I think it will be ok.
Does anyone have a Demon skeleton laying around?
- Thread starter tom999w
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I'm only one of a long lineage of shade tree mechanics that have been repairing cars in the dirt for a hundred years and ending with a good result. Sure, I'd love to have a frame jig and 60,000 square foot garage with a shiny floor, heat, and six lifts like some forum members have, but that isn't going to happen in this lifetime.
340sFastback
Well-Known Member
Oldmanmopar said he has a full body jig for A Bodies that correctly locates all the frame rails. Maybe he would lend it to you?
Right, but a "stick on the roof" isn't an accurately repeatable measurement. You're pulling a straight line off of a curve and measuring a distance with an angle on it. You have no way of knowing if that "stick" is level, and if it's not the measurement won't be repeatable. If I do the same thing but the stick is got a tiny bit more angle on it, the measurement will be totally different. And, oh yeah, the factory didn't tolerance the radiator support that well.
There's a reason why the factory chassis measurements are taken the way that they are. They are all based off of square, level surfaces so that they can be accurately reproduced. You have to be able to set up the reference points, otherwise the measurements are meaningless.
And just because the factory said the body measurements were within a 1/4", well, good luck with that. They aren't. Even if they were, the body lines being right doesn't necessarily mean your suspension points will be, and the suspension points being right is all that matters. The bottom of the radiator support that you use as a reference could be different by a 1/2" and it would effect nothing. The factory doesn't use it as a reference because it wasn't held to a strict tolerance.
And even if they did, how are you measuring that? The rockers are wider than the radiator support. So you're projecting a line forward, using an imaginary point, and then shooting a measurement line off of an imaginary point over to the bottom of the rocker? You've got no way to square that imaginary reference point, so, if any of the angles are a fraction off the measurement is useless.
Agree 100%. It would be one thing to change a single frame rail or other component like that, at least you have the rest of the car to use as a reference. Not best practice, but at least reasonable. But with that car he's got no reference points. None. Too much metal missing already. That means the references would have to come off a known surface (frame table, or yeah, at least flat concrete) to get accurate locations. Clearly our guy hasn't done any drafting, machining, construction, etc where you have to use dimensions established off a known reference point.
Right, except you could have moved the entire door frame up a 1/4" and the door would still fit. But now the rockers in the wrong place. Just because the roof line stayed the same shape doesn't mean it didn't move, not with the amount of structure missing from that car. You can stick the door on a fully assembled car if you jack up the front corner on one side only, there's too much flex even in a complete car for measurements like that to be accurate.
Look, I've done lots of work in the dirt, or in my backyard, or on a driveway that is most decidedly not flat. And that's fine, MOST of the time. When you do chassis work, you MUST have references that you can repeatedly measure accurately. If you replace one frame rail, you can do it in the dirt, level the chassis and use the rest of the chassis as your reference and measure one spot on the ground etc. and it will work well enough. Not ideal but you can make it work.
You have ZERO reference points with the body you have there. None. Nothing on that car can be trusted to be in the right spot. Which means you MUST have a known reference to establish the chassis measurements in the FSM, bare minimum. You don't need a 60,000 sq foot shop with lifts, but you do need at least a flat section of concrete large enough to hold that car so you can drop plumb lines and set your references to establish that "o-line".
Hell, I supposed you could frame up a "floor" with 2x4's and secure it on your ground surface there, and set that up so it's level and square like they do a raised foundation house or shed. Basically use that as a frame table, it wouldn't hold the chassis but as long as it was square and level you could use it to drop plumb lines to. Not how I would do it but at least you'd have half a chance at having some reference points.
In the ideal world your info would work great, but in the real life, establishing the O-line on any 55 year old car is just a guess. This is because you can see from the factory diagram that the O-line IS the centerline of the wheels. So the manual doesn't specify, but I GUESS these dimensions from the wheel centerlines to the frame (which moves up and down in relation to the wheels) are based on a fully loaded car (engine, transmission, interior, etc.etc. etc.), because the car WILL move up or down depending on what type of weight is on the car. So that blows the O-line dims right out the window. Also, what type of front and rear shocks are we talking about, and torsion bar tensions?? All those will affect the dimensions from the O-line to the frame points on that diagram.
So in the end, lets throw the dice on the imaginary O-line with movable dim distances, or throw the dice on taking three sticks and doing three simple vertical measurements. (Btw, if you lay a long stick on the roof, it doesn't wobble, it sits right sturdily on the roof as if you were laying it on a flat table).
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Nope. All the dimensions you need to establish the 0-line are clearly marked and it’s not a guess, the geometry is clear and repeatable.
All completely irrelevant. I’ll say this again, all the dimensions needed to establish the 0-line are clearly marked in that diagram.
That’s a chassis diagram. None of those measurements are ride height dependent. There’s a reason the suspension isn’t drawn in, it isn’t relevant for the chassis measurements.
Yes, they indicate the axle centers for the wheelbase measurements in the drawings. They show them because the chassis measurements establish those locations, not the other way around.
None of the dimensions in that diagram are moveable. The chassis dimensions set the axle location, not the other way. There’s no “roll
of the dice” to locate the 0-line, just math. Basic geometry.
Clearly, you don’t understand how to use that chassis diagram. Or why your measurements are in fact useless for your intended purpose.
Best of luck.
340sFastback
Well-Known Member
So laying a 2x4 on the roof to measure height of radiator support won't work?
jos51700
Green Bearing thread connoisseur
That roof isn't flat. I'm not seeing how using it is going to get you the measurement you're looking for. Whatever the angle of the topline is, is going to affect your measurement.
Besides, the reason all these dim's pull from with the wheels installed is because the body is going to sag when resting on wheels, so all body measurements are 'real world'. You can pull numbers off Corpse A to see how it compares to Corpse B, but it will change when it's on the wheels and the front subframes are loaded. Two cars won't flex the same and if yours has a frame issue, you might not see it until after everything's loaded IRL.
Besides, the reason all these dim's pull from with the wheels installed is because the body is going to sag when resting on wheels, so all body measurements are 'real world'. You can pull numbers off Corpse A to see how it compares to Corpse B, but it will change when it's on the wheels and the front subframes are loaded. Two cars won't flex the same and if yours has a frame issue, you might not see it until after everything's loaded IRL.
None of those dimensions depend on the car being on its wheels. Literally none of them.
The wheelbase measurements are determined by the chassis, not the other way around.
Those measurements are meant to be used with the chassis leveled and balanced side to side, not on its wheels and suspension.
From the FSM, the proper procedure for using those measurements
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Davco
Well-Known Member
Carthage Classic Cars in North Carolina will tell you the same thing as 72bluNblu. They posts very informative videos regularly. Lots of wisdom and their backlog speaks volumes.
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I'm sure you know that screenshot you took above is for horizontal dimensions, not vertical dimensions..
But anyway, just for information's sake, since you're saying the wheels have nothing to do with anything in that diagram, lets just delete them from the diagram... Then where is the O-line?
I literally circled the vertical dimensions in red on the diagram I posted before. I’ll post it again
The 0-line is exactly in that same place. 3.94” below the center of the rear shackle mount, 5.98” above the bottom of the front frame rail at the torsion bar crossmember measuring point, 1.24” above the rear K member bolt and 1.82” above the front K member bolt.
Yeah, I know, your car doesn’t have those 3 front points. But it doesn’t matter!!! If your car is on a level slab, you measure down from the rear shackle hanger to the floor. Let’s say you put your car 3’ in the air (this is an arbitrary number!). So it’s 36” to the O line, so the center of the shackle mount is at 39.94”. Now, you move forward. The 0 line is at 36”, the measuring point at the frame is 5.98” below that. So 36-5.98 and you need 30.02” from the floor to that measuring point. Now your crossmember is located, and you move forward and do the same process for the front rails at the K frame bolts.
But you’d need a flat and level surface to drop plumb lines to in order to measure that. But you can’t seriously do this work without that, or a frame table. And then you’d need to drop the plumb lines and measure the diagonals to get it straight.
This is chassis work 101. That project of yours is a BIG one, because of all the reference points you don’t have. It should really be on a frame table because of that.
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340sFastback
Well-Known Member
I thought you posted a while back you have a unibody jig / frame table for an A Body in your shop? That would be the best solution to the basket case rust bucket Demon dilemma.
All arguing aside, since no one had the dimensions I was looking for, and also since my car is not on a frame rack or level floor, I may have found the solution another way. I pumped up the back tires to their normal psi then leveled the rear axle (from left to right), then put a level between the left and right rocker and leveled them (from left to right), then put a level on the top of the firewall and leveled it (from left to right), then put a level on the bottom of the radiator support and leveled it (from left to right). So that leveled the car from left to right. Then for the front to rear tolerences I hung the doors and fenders and slightly adjusted the nose up or down to insure that all the door/fender lines were uniform.
And so far it looks beautiful, all the fender mounting holes line up nicely, and also the spot weld holes line up with the new panels. I also am guessing that the weight of all the new parts on the front end will stress/weigh down the front of the car, so I'm building a slightly bigger gap between the doors and fenders at the bottom, that will close up uniformly once all the front end stuff is installed.
And so far it looks beautiful, all the fender mounting holes line up nicely, and also the spot weld holes line up with the new panels. I also am guessing that the weight of all the new parts on the front end will stress/weigh down the front of the car, so I'm building a slightly bigger gap between the doors and fenders at the bottom, that will close up uniformly once all the front end stuff is installed.
He is not interested in anything I offered Parts or help and he bought the car down the street. The fixture is here sitting outside with nothing on it right now.
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Actually I’ve fixed several frames and assembled many car bodies in my life. You wouldn’t know.
No point posting pictures of my Duster, haven’t needed to replace any chassis members on that so it’s not relevant.
Not sure what your problem is, I said from the get go that car of the OP’s should be on a frame table so on that we’re in complete agreement. You being wrong about something unrelated in another thread that got closed is no reason to bring the argument here.
That’s a start for sure, but you absolutely can not expect to use the body components and those fits to locate your suspension points. It’s just not gonna be close enough. You could end up with great door and fender fits and a car that dog tracks down the road and can’t be aligned. The factory managed to get cars that had lousy body fits to have straight chassis’s, so there’s no reason why the inverse can’t be true.
You need to be able to drop plumb lines to a level surface. Ideally, you’d need something like that frame jig OMM has. But yeah I get why you might not want to deal with him!
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340sFastback
Well-Known Member
Wow that frame jig is on wheels could be pushed right onto a car trailer and be used anywhere.
It is built so ridged with heavy steel you can use it on a hill in your driveway. We have leveling legs to level it to use a level when building a body from rails up. We did not build the table . we bought it from Mario Andretti's 3n1 Race Works in NJ. It had a crane and pulling fixtures on it to straighten sprint car frames.
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