Rear frame rails sitting very high on rebuild

[72restocuda]

So in the process of a complete assembly of the rear of the cuda, built a frame jig, made the mounting points based on a datum line diagram of a 1970 barracuda, the rear mount should be at 15 7/16, well I can't get the rear quarters to line up even closely unless I crank the rear rails up to 18 3/4 - which is close to the middle of the rear frame rail height.  The jigs other mounting points are at at 6" in the middle and 14 5/16" in the front and is mounts just fine.  The rear deck height is also included - the hinge mount to deck is at 13 12" inches - so that's good also. Included are pics of the car on the jig and the datum diagram I used. anyone else have to crank their rear rails this high?

[Skdmark]

Check this thread out. It's a Challenger with similar issues regarding the datum drawing
https://forum.e-bodies.org/body-shop/5/rear-frame-rail-fitment/1544

This one has a reference to a 'cuda being closer to 18" in the back.
http://www.cuda-challenger.com/cc/index.php?topic=106373.0

The drawing show the rear frame rails having a curve around the rear axle whereas they essentially go curve up and go straight back. Gottz wonder if the drawing is wrong in that area.

[72restocuda]

Thanks, I feel like I'm going crazy, I'm ready to assemble everything but I welded the rear frame rails to the rocker panels at the approx 16" height like the datum drawing has it, then I go to put the rear panel and quarters in place and nothing fits, so I had to use c-clamps to keep the front part of the rear frame rails down to where they sit on the frame jig brackets - and then raise the rear part if the rear frame rails till the quarter panel body line are straight so now I need to cut wedges in my rear frame rails otherwise when I release the clamps holding down the front part of the rear rails where they connect to the rocker panels they start to lift. I hope that make sense - I can take pics
Thanks again
-Steve

[72restocuda]

Sorry to push this thread back to the front again, I just need anyone who has their cuda on a jig now to see if they can tell me how off my rails are, how off the datum diagram I have is.  If I should start a new thread fine.  Any help I really want to get the car in paint before the first snowfall otherwise its gonna have to wait till the spring
-Steve

[soundcontrol]

If I understand this right, if you put a long straight ruler on the the 2 X-6 points (from the drawing) on the frame rail and let it extend in the rear, and measure the rear rail at the D point, you should get the correct measurement -6 inches right?
So if you measure that way the D point measure would be 9 and 7/16 inches according to the drawing.
Then this could be measured on any car even not on a jig right?

[soundcontrol]

This drawing for a Challenger says 17,5", shouldn't it be same on the Cuda?

[72restocuda]

so you see my dilemma  - yes if you had a long ruler and put it to the bottom of the frame rails - it should be 9-7/6 up from the bottom of the front of the rear frame rail but its closer to 13" when I'm trying to get the rear quarters level, the imaginary datum line is the upper rail of my jig so the transmission crossmember and the front of the rear frame rails is 6" above that .  So one would assume the 15 7/16 would be ok, I tried that and no luck, put some screw jacks on the rails and kept cranking up till the rear quarters body line was laser level.   and I agree why would the challenger be any different - these cars have the exact same rear clip except for a 2" longer rear footwell, makes no sense, anyone on a jig right now that can tell me how high the rear rails are either compared to the front rails or some measurement that can answer this question for me, or should I replace my rear rails with new ones, mine are original and the only part not being replaced back their

[soundcontrol]

so you see my dilemma  - yes if you had a long ruler and put it to the bottom of the frame rails - it should be 9-7/6 up from the bottom of the front of the rear frame rail but its closer to 13" when I'm trying to get the rear quarters level, the imaginary datum line is the upper rail of my jig so the transmission crossmember and the front of the rear frame rails is 6" above that .  So one would assume the 15 7/16 would be ok, I tried that and no luck, put some screw jacks on the rails and kept cranking up till the rear quarters body line was laser level.   and I agree why would the challenger be any different - these cars have the exact same rear clip except for a 2" longer rear footwell, makes no sense, anyone on a jig right now that can tell me how high the rear rails are either compared to the front rails or some measurement that can answer this question for me, or should I replace my rear rails with new ones, mine are original and the only part not being replaced back their

I believe the Barracuda D measurement is wrong in the drawing. Someone even said in one of the linked threads that it should be 18". My Challenger body is on a lift, I can probably measure that with a laser, but not until next week, I'm away for work this week.

[soundcontrol]

I measured my Challenger with a laser. In the rear I have 281mm (11.06 inches), if added 6" for the datum line my measure is 17.06 "
At the highest point on the rail in the wheelhouse I have 322mm (12,67 inches), add 6 and it's 18,67". (that is 18 5/8")

So my measure in the rear is 1/2" off the Challenger specs, but it could be a slight error in the laser, it was hard to get it exactly correct on the 2 reference points
and a very small difference there makes a bigger diff in the rear of the car.

[Cudajason]

 Here is my less scientific measurements form my Cuda while in the ground.

[72restocuda]

thanks so much, I was speaking with a guy taught me the importance of this diagram.  the body line is the more important measurement than the rear datum point "D"  - at point on the frame assembly diagram "E"which is the inner lower leaf spring front shackle mount this sits 5" below the body line, Point "G" which is 2.75 inches in front of the center mark of the rear shackle mount is 8" above the body line.  So these 2 points are 13" apart.  As long as you have these 2 points at these measurements the rear datum point isn't as important and because the different years may have a different body line height and therefore a different point "D" on the datum chart.  At least that's what I got from the discussion

[RacerX]

Those Harry Depew diagrams are pretty much garbage.    They were drawn by the aftermarket
in the 70s when there was no other available reference and as some have noted they got a few
things wrong.

Another wrong measurement:   Notice the 63 3/4 diagonal.   On the diagrams it is the same between
Challenger and Barracuda.  But how can that be when the Challenger is 2 inches longer?    Rewriting
Pythagoras' theorem are they?   

I am not sure I would trust any of the numbers on these...

The last one posted is from the Mopar service manual and I have a lot more faith in that one.