Welded SFC's - Need to Realign Subframe

[First Bird]

Stupid is as stupid does. I did not use the gage holes when I installed my subframe. Instead, I ONLY measured diagonals from the Fischer Manual (and LCA zerk to leaf spring mount, etc) using a plumb bob, tram gauge and measuring tape. I had read that gage holes could be unreliable and that measuring diagonals was surefire. Now I can't get the hood opening square as I reassemble my 1968 Firebird (even with radiator support shifted all the way over). What went wrong is the driver side frame is ahead and the passenger side frame is behind the gage holes. I figure the frame is square but not parallel to the body work. Does that make sense?

I need to realign a subframe with welded subframe connectors. Here's my plan. What do you think?
1) Un-weld welded subframe connectors. Maybe borrow plasma cutter.
2) Leave front body work on. Loosen bolts at radiator support
3) Put jack stands under body rocker just below/behind firewall. Also put jack stands under rear axle.
4) Unbolt Exhaust From Headers
5) Remove Hood
6) Lift Engine just off the cradle
7) Loosen subframe bolts
8) Line up gage holes
9) Measure diagonals again, including diagonals of hood opening
10) Tighten subframe bolts.
11) Re-measure diagonals to make sure nothing shifted
12) Re-weld SFC's

Background info:
Before disassembly, a frame shop straightened the rear frame and measured the front subframe OK.
I used solid subframe bushings and welded in DSE SFC's.
I installed the Engine/Trans/Exhaust.
Fender to door gaps are good.
In searching internet and PT forum I find people have removed the subframe entirely without removing front body work. So I figure I don't have to remove front body work to just loosen and shift the subframe.

[MrQuick]

Tough one...if you had the frame aligned on a frame machine then I would leave it where it was tested. That would ensure your tracking alignment is true. Which imo would be more important. You can fudge the body alignment.

You can modify the radiator support and bumper bracket holes to align the body square to the assumed aligned frame. How far off would you say it the gauge holes are? I inspected an original 71 Formula years ago and the holes were off by a 1/4" and that was from the factory. Alignment shims were not far off left to right.

If you had to yes you can shift the frame with the body work on. A come along, chain and sturdy tree maybe necessary.

[First Bird]

Thanks for your time and replying.

Tough one...if you had the frame aligned on a frame machine then I would leave it where it was tested.
It WAS aligned. But then I took the subframe off and re-installed it crooked when I relied on only diagonals, not gage holes.


How far off would you say the gauge holes are?
Inch forward on left. Inch rearward on right.

Glad to hear your opinion that I can shift subframe with body work on.

[LUV2XLR8]

i would get the correct gaps in the body lines first... then install the sub-frame.. once you got everything where you like it ... then burn in the connectors... that's typically the last step

[First Bird]

Gaps are correct. Connectors are burned in.

[exwestracer]

Gaps are correct. Connectors are burned in.

So by your previous post, the gage holes are 2" off from each other? Not sure how you got the diagonals to come out right, but that's past history. Before you cut it, check the wheelbase from ball joint zerk to rear axle tube on both sides. if one side is correct, leave that side partially connected and make it all up on the other. That way you can at least have some partial reference. At this point, I would hang plumb bobs from the rear axle flanges and the zerks while you are fixing it. Keep checking that the length and diagonals are correct to keep the front and rear axle centerlines straight and square.

[First Bird]

Ray- I appreciate your suggestions. I'll do all of them. Yep. Gage holes are off 2" from each other. I didn't measure side lengths. Thought diagonals would be enough. The CE solid subframe bushings I used are just spacers - they let the subframe rotate relative to the body. I now have GW solid bushings. Will use your method, including measuring side lengths and I'll get it right.

[First Bird]

Here's how it worked out. First, thanks to Mr Quick and Ray for your advice. I was able to leave the fenders on, the engine in with the exhaust on. This saved a ton of time. I took the engine weight off the frame with an engine hoist. I ended up cutting both connectors with a reciprocating saw. I made diagonal cuts that followed the weld. The angle of the single cut wouldn't let the subframe drop enough to install the new GW bushings. So, I ended up making a second cut an inch fwd into the subframe. This worked. I installed the new bushings one side at a time. Using plumb bobs, I centered L and R gauge holes and came up 3/8" off diagonal and 5/16" off side measurements. After a few of hours of shifting the frame around and measuring carefully, on the 8th round I got sides equal and diagonal 3/16" off. Nothing I did, shifting, prying, and changing plumb bob locations could reduce that 3/16" difference in diagonals. I'm going to wait till the car is on the road and I get the alignment dialed to re-weld the connectors. It turns out that un-welding welded SFC's isn't so bad. But if I had to do it again I'd make a vertical cut.