I just took some measurements on my frame and the front support hole is centered from side to side. All the diagonals on my frame are identical from side to side as well.

 

what were your measurements?

 

I was getting around 26" from center hole diagonal to diff hat center. Center hole to outside of rear frame was 24" and to my trans crossmember was about 36" but I am not sure what point you measured to on that one.

 

I was trying to figure out if an offset is built into the overall frame or into the crossmember that hangs the diff or is there none at all stock back there! Your bracket centers with the front frame sections 26.5 both sides, but the back upright on one side drivers seems further out 26.125 diagonally and would be further back also from the other side which was closer at 24.125 diagonal. therefore it looks like the whole back section was put on roughly one inch toward the drivers side, when my thought are if we had a factory offset for the drivetrain designed into the overall frame, it would be shifted the other way toward the passenger. I wanted a measurement from both directions also to those sombrero hats from back frame rail and since the front section seems good, from somewhere on back. I think the one picture where you were looking for the sombrero to frame is a good measurement that you were pursuing. I want to see where those hats sit front to back.

The measurement on the crossmember I was looking for was the other side from the end to mounting holes to see if there is any offset there in that crossmember. The big holes don't tell me much, because i am interested in the holes that mount your diff.

On your car in comparison with the overall frame dimensions posted you should verify the 69 3/16 and the 104-1/2 or the measurements from front to the sombreros that I asked for above.

I could see that back section getting hit and pretzalled and just the entire getting cut off and someone going to a junkyard and getting a new one and welding it on, but got it shifted wrongly when they jinged it on, but squarely. Therefore need to know if those sombreros are set front to rear at different distances. I don't think so, because it would as per your measurements push the diff nose, more pointed toward the back of the driver' seats. i wonder if the tires/rims have less clearance to the rails on the driver's side!

 

I think there might be another possibility. I was looking at my snubber mount bracket and where yours has a hole, mine has a bolt. I wonder if your bracket is simply mounted wrong? That offset, assuming that the brake line retainer hole would be used, would be just about the same amount as the hogged out hole. I tried to get a pic but my differential is still in place. Should be out by this weekend.

 

i thought that as well but what troubled me was that the nose of the diff, the u-joint, was very close to the fiberglass body on the drivers side so that told me that the rear is pointed in the wrong direction. It also puts the half shaft u-joint close to the body as well on one side due to it being cocked. i am sure chevy wanted the nose to be centered in that body opening.

I put an email into a local body shop that also specializes in vette restorations & has a frame rack asking for ball park prices to check and to possibly fix the frame either with the body on or off. not that I have the extra cash right now.

 

so is this what you want (see blue line)?

 

but also from somewhere farther forward and the measurement back to the sombrero also. trying to figure out if that crossmember is being forced to be installed crooked (slightly angled). From somewhere in the front measuring back to the sombreros is more important

So if those measurements end up being square or close enough, I then would just reposition that frame mount bracket and call it a day. If not square, then a sombrero will need to get repositioned is where I am at!


See your 22.875 and 23.875 is why I think your car got a new A$$ part of the frame. The bracket itself looks like it is centered from your 26.5 to 26.5.

Lastly I personally wouldn't think the diff would be mounted offset based on handling and standardization of the halfshaft lengths etc. but i am pretty sure some was put forward for the mounting of the engine to offset the driver, because i have heard other guys say that, but I have never explored whether our cars have an actual offset by actual measurement until this thread! Your rear portion of that frame based on the 22.875 and 23.875 if accurate tells you that back portion is shjfted one inch toward the driver, but your diff nose is trying to come in from the passengers side.

Why I am calling it square is first your two 43.750 measurements in combination with the 26.750s

 

Try that (yellow). on each side.
It'll tell you if the frame rails are the same length side to side.
Then make front to back measurements in various places getting progressively shorter.

to me it looks as if the pass side was hit around the wheel somewhere. Slid it into a curb or rocks or something. Is the pass side rear bodywork original?

Back piece might be 43.750" wide in two spots, but if its not square that may throw off the diff mount hole to one side.

dodosmike

 

try the purple x measurement as well.




Whatcha get there? If its the same BL to FR and BR to FL then that portion of the frame is square.

 

I stopped by a friends shop that builds custom 4X4 monster trucks and explained my situation to him. he said F**K the side to side measurements...X never lies! As you guys stated too, so he thought the same as you and I do, that the car was hit or curbed in the passenger side rear tire and the back frame horns are off. he told me to X like you've shown here and it's about 7/8" off (+/- 1/8th) as my back was killing me (sunburn) and it was hard to hold real steady.

also talked to a guy with a frame table but he's busy for awhile, he said ball park I'm probably looking around $500 to hopefully get it straight 1 full day + 2hrs to secure & square it to the table,2 hours measuring and the other 4 hrs for pulling) and suggested taking the body off or at least loosening the body mounts during the pull to not stress the body.

so now I'm at a cross roads as to removing the body or not?

 

because you had some X measurements already, so we were at trying to figure out the origin points of your existing x measurement starting points!

But more x measurements would be even better! :I agree: I really don't think you are that far off! I guess when I get some free time, I will go see on one or both of my cars, if that diff is offset at all, which I doubt.

Lastly, from your measurements, it may have been hit originally, but it doesn't seem like that is the problem now, because I think the fix was the problem and the evidence of the hit isn't there anymore!

 

agreed I can get a better X measurment when I can lay on my back with out pain (sun burn) and have some help from my son this weekend. I appreciate the help with measurments on your cars as well as the advise. as stated this was supposed to be a moderate clean up and drive project and it would have been if i didn't hit this road block.
sucks to see all new 17" wheels & tires + all new suspension parts,bolts,newly painted frame etc and the project has stopped
for now, till I get re-motivated & get a new plan.

 

finally got under the car & the back is definitely out! I can't see where the hit was or any repair for that matter? nor do i understand how the body mount are all lining up with out being crooked?

If I decide to pull the body off the frame to get it fixed would they want just the frame or would they want the rolling frame? If the rolling frame, would I just loosely bolt in the rear & suspension to get it rolling or would they need it all pretty tight?

If I am gonna pull the body I will pull the engine/trans out to get it them freshened up + repainted etc.
my X measurement from the rear corners as shown are 72" one way & 70.3125" the other way so it's out 1.6875". I can't believe the old owners were running it like that, with the rear cocked & drive shaft on angel! I don't believe in half ***'n anything, do it the first time & do it right.
I always wanted a vette and I'm vested in this one so I'm gonna stick with it even though this hurdle blew my plan to be on the road this summer.
paul

 

a guy at work has a buddy that does frame work on the side. he is retired but ran a frame rack for a big outfit locally for 25+ years. he said he need to see the vette first but maybe able to help me out with out pulling the body off.
he has a complete floor pot set up & the hydrolic aparatice that connects to it + the experiance. If its just the rear horns that are out & not themain frame too, I just may have to disconnect the rear body mount bolts & bumper bolts and he can pull the back?
so maybe I'll get lucky and not have to take off the body????

 

One thing to consider is how much do you want to pour into fixing this?

Id pull the body and attempt a fix that way. However this will lead to "while I'm at it's" and cost that much more. I'd get the diff centred as much as possible get the body mounts close and call it good.

Now, figure out how much money all this is going to be and compare it to a new frame, stock or a SRIII frame.

Is this a long term project or something your trying to keep on the road as you work on it?


My '78s front frame was 90* vertical to the rest of the frame. I parted it out. If I was doing it again id have bought a SRIII frame and made a pro-touring Vette out of it.

Dodosmike

Edit.
Is the rear crossmember bowed? Is the middle portion of the crossmember higher or lower than the ends?

 

last thing I want to do is pull the body, this was supposed to be a nice weather cruising car not a restoration or a show car. the frame is cherry, no rot or flaking rust, just had surface rust that came off with a wheel. the lower bird cage is the same way even has paint still on it inside. the body is nice (needs paint) and the engine & trans work fine and the interior is original,intact & un-ripped.

I'm gonna let my buddies friend look at the car & see if he feels he can get me back on center or atleast real close. If he can pull the frame in the right spot & move that differential center line that 3/8"-1/2" I need, and I don't have to pull my body then I will call it good.

 

FYI-couple new developments for those following along & helping me out.
I took a string measurement & a tape measurement tonight from the center frame hole on the front engine cross member to the inside edge of the outside frame rail in front of the rear tires (see red lines on print). both the string & the tape were right . not a perfect way to do it but i think my front frame is fine.
I also took the same action and went from the center hole up front to the center of the rear cross member mounting bolts (sombreros) and they are off 3/4" father back on the drivers side (see blue lines on print).

I also noticed that the inside rear splash guard or rear wheel well is away from the rear quarter panel about 5/8" in the middle & the gap was filled with bondo, the other side is tight against the quarter panel. so I guess that frame was hit in and back?
Paul

 

I think your on the right track, getting the frame pulled close to where its supposed to be.

If I were doing it I'd remove the #3 and #4 body mount bolts to reduce any tension on the body when the frame is manipulated straight(er).

Maybe even remove the rear bumper cover to avoid stress cracks in the paint.

dodosmike


At least your not dealing with this mess:

 

Sounds like you are on the right path. Now just wait and see what the frame guy can do.