Frame Rail/Body Alignment to Baseline - Vintage Mustang Forums
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post #1 of 7 (permalink) Old 02-07-2019, 08:37 PM Thread Starter
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Frame Rail/Body Alignment to Baseline

I'm working on a 68 coupe that has some accident damage. I'm trying to establish how the body level front to back should be in reference to the frame rail baseline before I start building a jig to put everything back in its correct location. If I level based on the assumption that the rocker panels should be parallel to the baseline, the frame measurements are waaay off. If I level according to the frame dimensions (I can only get them to within +/- 1/4"), the rocker panel is 1/2" higher in the front than the rear (measured from the front to rear of the door). Anyone happen to notice the same? I'm leaning towards leveling with the frame as close as I can get it, but was hoping someone more knowledgeable than I could tell me if that's the right way to go. It seems odd to me that the rockers wouldn't be parallel, but I honestly don't know. I suppose that suspension loading differences would bring the overall body back to level, but was hoping someone out there might be able to shed some light on my conundrum.
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post #2 of 7 (permalink) Old 02-07-2019, 08:49 PM Thread Starter
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I forgot to post another picture that made me question the whole thing in the first place. When I lay my export brace in place, there is a significant gap at the front of the shock towers, close to 1/2". If the front rails rotated up in the front to close the gap, it would bring the rocker panels closer to level, hence the question.
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post #3 of 7 (permalink) Old 07-17-2019, 08:07 AM
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I'm currently running into a similar issue. Did you figure out a solution?


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post #4 of 7 (permalink) Old 07-17-2019, 09:50 AM
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I am also interested in hearing what others have to say about this. I am a long way from getting to this point, but have been contemplating how to make my jig as I continue stripping the car down. The whole underside of my car is coming off, but the rockers actually seem in pretty good shape and all of the gaps seem pretty good right now.

Hopefully I will continue to gain more understanding and enlightenment as I disassemble everything. But from my initial research, it looks like the rockers should run parallel to the datum line and the front frame rail to radiator support is slightly inclined from firewall to radiator.

I plan to use the "whole floor assembly", core support, strut braces, etc... I am going to order everything and have it on hand BEFORE I start taking anything out. I am just starting to develop a plan for some type of jig to keep the body in position and sliding the floor assembly underneath. Or more correctly, I will probably use my lift to position the body on top of the floor assembly. Lots of thoughts in my head, but no real plan yet.

Looking forward to hear how this pans out.

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post #5 of 7 (permalink) Old 07-17-2019, 10:09 AM
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I would take it to a body shop with a frame table/platform and get them to check and straighten it and tack in some bracing.
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post #6 of 7 (permalink) Old 07-17-2019, 10:09 AM
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If you have not supported the chassis correctly, you will never get good dimensions. 4 jack stands do not provide enough support for the front or rear of the chassis. Depending on what area of the car you are repairing, it should be supported in numerous places, not just at the torque box areas.

When you use the body measurement charts the datum line that they are referencing is not level to the rockers. Me personally, I built my chassis fixture to locate major assemblies; front frame rail, front of torque boxes, front leaf spring mounts and rear cross member, everything square and level. I set the chassis level at the rockers and use a laser level for the datum line underneath the car. It is much easier to have the rockers level than set at the datum line, as you are discovering. These cars are not accurate and have been subjected to who knows what all in their lifespan. Using plum bobs and tape on the floor to check the cross reference dimensions (a tram would be easier) and a metal ruler along with the laser level will get you fairly accurate dimensions without a second hand. You will find that these dimensions are all over the place and if you are replacing major structural items like the front frame rails, measure and reference all known dimensions and record them so when you go back together with new parts you can correct issues that might have come from the factory, much less collisions and other damage. Also note that some of the dimensions on the body measurement charts are not correct. Take the time to fit body parts, measure for square, use sheet metal screws before welding anything and double check all work before welding it up.
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post #7 of 7 (permalink) Old 07-17-2019, 01:54 PM
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I have the front chopped off my 66 right now due to old accident damage. So measurements of the front with the old sheet metal are useless... I am just now getting the front floor supports into place.

The best place to support the car is by the pinch welds and get those all in place. The problem with that is if you are using jack stands the car won't really be high enough to work on. Which is my problem right now... Ideally you could support it by the pinch welds and then be able to tie it down to the floor so it doesn't move...

As for measurements. You will not be able to rely on one drawing. There is no one drawing with all the dimensions and you need to cross check with others as there are different measurements due to some being wrong or measuring from a hole that does not exist. I have had to get the dimensions from a later model for the front floor support across to the rear frame rail because the late 66 only has the rear indexing hole... Like mentioned cars back then were not very accurate. They build cars like houses using tape measures that didn't have markings smaller than 1/4"

Here is another drawing I found that has some info that others don't have.

Your export brace gap could be just the brace itself not having the right angles. Also that nose will tend to dip when you support the car by the front of the rocker panels. because that whole nose is designed to be in compression against the firewall not in tension.

On mine once all my front end parts come in I will work at getting them all fitting where they should be and get it welded together. Then I will throw together a stand that supports the car by the front leaf spring bolts and the LCA bolts so I can get the car high enough off the ground to easily work on the quarters etc. I will also look at making it roll on it's side so I can strip and paint the bottom.

Oh and I made up some simple quick trams for playing with alignment of parts using some scrap oak and maple sticks. I found sockets the same size as the alignment holes and attached them at the proper distance. They work great for initial verification of placement. I am going to pick up some 1" aluminum tubing from a friend and make a couple permanent rods that can't move.

Shoot me a PM if you have any ideas you want to bounce off of me. This is my first mustang but i have done other cars in the past usually with the luxury of a real frame though. My build thread is here
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