How to Check Uni body for Straightness

-
Shakedownscott

Shakedownscott

Well-Known Member
Joined
Dec 31, 2017
Messages
49
Reaction score
22
Location
Vermont
I am working on repairing and stiffening my '69 Barracuda front frame rails and torsion bar cross-member. At one point in her life someone cut holes in the torsion bar cross member to install fender-well headers.

40796827851_fc94a7ddde_o.jpg
20171223_140808 by shakedownscott, on Flickr

They also cut out this sheet metal piece below the firewall, that connects rockers to the frame rail.

26926809238_ddca7e9ce8_o.jpg
20171223_140709 by shakedownscott, on Flickr

There is also some rust in a 10" section of the front frame rail right in front of the torsion bar cross-member.

26926809028_2e1792ecfe_o.jpg
20180304_152249 by shakedownscott, on Flickr

Before stiffening these areas I want to make sure that everything is relatively straight. I have her on 4 jack stands two on the frame rails in front of the K frame. Then two in front of the rear spring mount on the rear frame rail.

I know the floor in my garage isn't totally flat or level. Laid a 4' level on the floor and there is a bit of a crown to the floor under the car. I have never driven the car so I don't know if it runs straight or has any real issues. I am a bit concerned about it potentially having some twist because it has a 440 in it combined with the holes cut for fender well headers.

Any suggestions on leveling her out and checking to she if shes square and straight?
 
You need some frame diagrams and take some measurements. The factory service manuals have them in the back if I remember correctly. You can use a tape measure or tram gauge.
 
With what I'm seeing as far as corrosion, replacement rails and trans cross member would be in order. They are pretty far gone. By time you clean those up you'll come across much more perforation, damage, etc. Those forward most pieces that run from the inner rocker to the rail that have been cut need to be replaced. In essence it ties the rocker, floor, and rail together into the front torsion box area. pretty important for stiffness. Big block cars usually had an extra torsion box plate/reinforcement in this area. Height measurements are hard to establish without a level surface to establish points from such as a frame plate/jig or a frame machine and related measuring equipment. On a frame sheet everything is referenced from a datum line. All the length measurements are referenced along this horizontal line and the height measurements are referenced up or down from this line. You can take some quick comparative measurements with a tape and comparative side to side but those measurements you get will be off from a published frame sheet because you're measuring on different horizontal planes.You can drop plum bobs from frame holes, mark the floor, and take the lenghth , width , and x measurements that way for a little more accuracy. A rail being up or down might or might not change a length or width measurement which is why you really need 3D measuring. Always start under the "cabin" Square, length, width, and height, and then move towards the ends.
 
Last edited:
I have issues in similar spots on my 67. I had just about the same holes on the bottom of the driver side rail and a poorly repaired torsion bar socket. I went with safe-t-cap caps for both pieces, the ones I got from them cover every area that your car seems to need. The people were super nice too. I have them preped and ready to install when it gets a few degrees warmer. The car is up on stands and I plan on running a straight edge as far forward as I can from rocker to rocker and find level, then as far back as I can, find level, and finally a straight edge across the two of them. A bunch of squares of different thickness plywood (underlayment, 1/2,3/4) and should be able to get pretty close, depending on grade of the floor. Figure after that make sure the radiator support is level and call it macaroni. Not sure if this is correct, but that is what I am currently doing
 
Basic squareness is pretty easy to determine. Pick four corner spots and measure precisely opposite corner to opposite corner and then the other opposites. The measurement should be the same.
 
Also a good bodyshop with a frame measuring system could set it up and measure out the frame.
 
WayneShelton said:
Also a good bodyshop with a frame measuring system could set it up and measure out the frame.
Click to expand...
Most shops charge about 2 hours to set one up and measure it. If you find a shop that has Car-o-Liner equipment it can be done on a lift and if it has a bolt head or hole it can be measured. It can calculate ball joint set back and comparatively measure and triangulate control arms, and measure spindles. Very useful piece of equipment when it comes to diagnosing, finding, and repairing damage.
 
Thanks everyone for the replies and helpful information. A tram gage looks like a useful piece of equipment to help figure some of this out. This gives me a lot of food for thought on going forward with this part of the project. Figure I am going to have to create a level plan under the car to measure any heights from/ As well as check the level and squareness of the body and frame.

I am going to add front and rear torque boxes after I repair the existing damage to the rails. I purchased safe-t-cap pieces to go over these sections after I cut out the rusted areas. They are pretty beefy and will definitely stiffen this area up.

I figure I have one chance to get this right after its welded up, its pretty much not going to be easy to correct. If anything is twisted or I don't feel confident in my measurements, I will send to a body shop to straighten and weld this up for me.
 
Shakedownscott said:
Thanks everyone for the replies and helpful information. A tram gage looks like a useful piece of equipment to help figure some of this out. This gives me a lot of food for thought on going forward with this part of the project. Figure I am going to have to create a level plan under the car to measure any heights from/ As well as check the level and squareness of the body and frame.

I am going to add front and rear torque boxes after I repair the existing damage to the rails. I purchased safe-t-cap pieces to go over these sections after I cut out the rusted areas. They are pretty beefy and will definitely stiffen this area up.

I figure I have one chance to get this right after its welded up, its pretty much not going to be easy to correct. If anything is twisted or I don't feel confident in my measurements, I will send to a body shop to straighten and weld this up for me.
Click to expand...

What are you going to do to arrest the rust inside and outside of the boxed sections prior to welding on caps? The caps you have can be coated with weldable sealant/paint prior to install and sealed along the welds after.

Have you looked at the US Cartool site? I would consider doing your car in a similar fashion as their body in white. Replacing the crossmember and other sheetmetal rather than capping it?

There's another similar site that has even more actual replacement components rather than capping the old ones. They specialize in rust repair parts, but I can't recall their name. Maybe someone here will. There is also AMD.
 
GeorgeH said:
It doesn't reference the height measurements.

Just an example, You could have one rail up a 1/2 in and one down a 1/2 and the length and width measurement specs be right on the money ,but you have an inch of twist in the front end.
Click to expand...

Yes, no "z" dimensions, but x and y dimensions can be verified....
 
I would like to clear something up here. There is some really good information here that I agree with BUT...
Technically speaking, the term "twist" only exists in the center section of the automobile.
If the center section is square then every thing else as far as datum is concerned is called high rail or low rail.
You could have what might be considered as a high rail but it would be corrected by straightening the center section that has a twist. This is why we work from the center section.
 
Same holds true with a diamond condition. You might think you have sway but straightening the center section diamond may correct some or all of what you consider sway.
If you have a diamond in a uni-body the automobile is most likely junk.
 
You could rig up some kind of scales with straight bars between them set to the same height from side to side and hang them off of the rocker panels, front and rear, to check for twist or barrow some centering gauges and learn how to use them.
If the center section is square and the sheet-metal fits, your good to go.
Now all you have to worry about is wheel alignment.
 
jbc426 said:
What are you going to do to arrest the rust inside and outside of the boxed sections prior to welding on caps? The caps you have can be coated with weldable sealant/paint prior to install and sealed along the welds after.

Have you looked at the US Cartool site? I would consider doing your car in a similar fashion as their body in white. Replacing the crossmember and other sheetmetal rather than capping it?

There's another similar site that has even more actual replacement components rather than capping the old ones. They specialize in rust repair parts, but I can't recall their name. Maybe someone here will. There is also AMD.
Click to expand...

For the rusted part of the frame rail I am planning on cutting out the lower rusted section. Then sandblasting inside and out the best I can followed by epoxy primer and paint. Im going to epoxy primer and topcoat the cap too. Where the weld bead is gonna be I plan on using a SEM weld thru primer.

For the torsion bar its pretty much the same except to clean out the sand from the inside since the bottom is not rusted that much. Then spray either cavity wax or Eastwood internal frame coating inside the cross member.

After that I will use some sort of oil under coating on the inside of all the frame rails and cross-members. Still experimenting with some different types of internal frame coatings and oils for undercoating. Once I sprayed the underside of a truck with rubberized undercoating and then sprayed hydraulic oil over that and it ate the undercoating and it all fell off. Trying not to repeat that failure :)
 
Shakedownscott said:
For the rusted part of the frame rail I am planning on cutting out the lower rusted section. Then sandblasting inside and out the best I can followed by epoxy primer and paint. Im going to epoxy primer and topcoat the cap too. Where the weld bead is gonna be I plan on using a SEM weld thru primer.

For the torsion bar its pretty much the same except to clean out the sand from the inside since the bottom is not rusted that much. Then spray either cavity wax or Eastwood internal frame coating inside the cross member.

After that I will use some sort of oil under coating on the inside of all the frame rails and cross-members. Still experimenting with some different types of internal frame coatings and oils for undercoating. Once I sprayed the underside of a truck with rubberized undercoating and then sprayed hydraulic oil over that and it ate the undercoating and it all fell off. Trying not to repeat that failure :)
Click to expand...
Best Ive seen Corrosion Inhibiting Compound Kit | Like90 Products
 
You can level the car by shimming the jackstands between the frame and stand using some scrap metal for shims.
 
Bodyperson said:
You could rig up some kind of scales with straight bars between them set to the same height from side to side and hang them off of the rocker panels, front and rear, to check for twist or barrow some centering gauges and learn how to use them.
If the center section is square and the sheet-metal fits, your good to go.
Now all you have to worry about is wheel alignment.
Click to expand...

Thanks for all of the help Bodyperson. Didn't understand the significance of getting the center section square etc. Checking for a diamond condition seems pretty straight forward, kind of like taking corner to corner measurements when framing a wall.

If I understand what you are suggesting for twist, I would measure a set distance down from the rockers on both side of the car. Then run a straight bar from side to side in the front at that distance and then do the same in the back. After that I would run another straight bar between the front and rear bars and see if both sides of the car are level to each other?

This sounds the same as what the Great Ronzini was saying above.
 
Shakedownscott said:
Thanks for all of the help Bodyperson. Didn't understand the significance of getting the center section square etc. Checking for a diamond condition seems pretty straight forward, kind of like taking corner to corner measurements when framing a wall.

If I understand what you are suggesting for twist, I would measure a set distance down from the rockers on both side of the car. Then run a straight bar from side to side in the front at that distance and then do the same in the back. After that I would run another straight bar between the front and rear bars and see if both sides of the car are level to each other?

This sounds the same as what the Great Ronzini was saying above.
Click to expand...
Yes that can tell you if your height is even but not necessarily correct. So many other variables.
Here is a whole book about centering gauges. http://www.chiefautomotive.com/manuals/accessories/UGMS Users Manual.pdf
 
Bodyperson said:
Yes that can tell you if your height is even but not necessarily correct. So many other variables.
Here is a whole book about centering gauges. http://www.chiefautomotive.com/manuals/accessories/UGMS Users Manual.pdf
Click to expand...
Back when I was using centering gauges, I rarely used the "datum" spec. If length and width is correct, the sheet-metal ultimately set the height.
Then there is the upper body that can still be bent after the frame is straight.
In collision repair we try to get it all diagnosed at once and virtually reverse the collision.
 
Last edited:
Thanks Bodyperson. There is a lot of great information in that book, will take a while to digest all of it, but should give me a good idea of what im looking for.
 
GeorgeH said:
With what I'm seeing as far as corrosion, replacement rails and trans cross member would be in order. They are pretty far gone. By time you clean those up you'll come across much more perforation, damage, etc. Those forward most pieces that run from the inner rocker to the rail that have been cut need to be replaced. In essence it ties the rocker, floor, and rail together into the front torsion box area. pretty important for stiffness. Big block cars usually had an extra torsion box plate/reinforcement in this area. Height measurements are hard to establish without a level surface to establish points from such as a frame plate/jig or a frame machine and related measuring equipment. On a frame sheet everything is referenced from a datum line. All the length measurements are referenced along this horizontal line and the height measurements are referenced up or down from this line. You can take some quick comparative measurements with a tape and comparative side to side but those measurements you get will be off from a published frame sheet because you're measuring on different horizontal planes.You can drop plum bobs from frame holes, mark the floor, and take the lenghth , width , and x measurements that way for a little more accuracy. A rail being up or down might or might not change a length or width measurement which is why you really need 3D measuring. Always start under the "cabin" Square, length, width, and height, and then move towards the ends.
Click to expand...
Unbelievably the correct response, word for word.
 
You must log in or register to reply here.
-

Back
Top