79 firebird front sub frame alignment
 

Hello I have my firebird on a frame jig and I have just installed the front sub frame. I have put a level on the legs that go back under the seats and it shows a slight nod or drooping forward. Not much and would only notice using a level. Ok this is in the air and not on the ground . My question is how important its this frame to be completely level for fit up/gapping etc.... Does it even need to be perfectly level? THats why we shim? Can I shim the sub frame? just leave it? Im using global west. solid mount bushings. Or once its one the ground again everything will shift? Maybe the floor pan its not right, its screwed in at the moment .. thanks

Perhaps the body isn't level. If the body bushings are the correct thickness, install and go. No shimming on production line, that was done at panel stage, if at all. Once on the ground it will stay the same as when mounted. Also, it's very easy to adjust these mounts on a complete car should you later decide to tweak them.

OK Update because I know you all have been waiting.....The rear mounting holes are off about 1/2 in..I believe I have bought a pre 1975 frame and this is why things are not lining up....Also measure F in the fisher Manuel is different from what I have on the frame. SO what to do, should I modify the holes or start looking for another?

There are some threads on how to use the wrong year subframe either here or on pro-touring.com. I believe the poster was NotaTA. I don’t believe it's a big deal to modify one. Especially compared with starting over with a greasy, rusty unloved one.

Well I'm convinced that the subframe is correct. I again I'm off by 1/2 consistent on both rear mounts. I doubled check my measurements from the fisher manual. So iv come to conclusion my replacement floor brace is off some how. Iv decided to move the captive nut forward the distance required and call it good. So I cut the floor and noticed there is zero rust prevention coating. So something to watch out for. This was from firbird central, not knocking the place I like them , just something to keep in mindAttachment 626472

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Is it off 1/2" front to back? Side to side? Can't really tell by the picture.

Had you said that you had swapped subframes with an unknown and now nothing lines up we'd know what to tell you. But often details are so vague we have to guess to know if even giving advice or free post bumps. New subframe? Replacement floor brace? Why would there be rust prevention, they are only a seller, like all other shops. It's not their item. Correct, knocking them would be dumb. Did you need to cut the floor anyway for broken captive nuts or really didn't like offset hidden body mounts hidden inside a chassis rail?

http://forums.maxperformanceinc.com/...d.php?t=839344

Check also the bush holes since I believe the earlier frames used a smaller type than later.

Ok here is what I got. I made some offset captive nuts. Looking at the pictures ypu can see the bolt hole is forward of the brace. I'm using solid mounts BTW. I also noticed when the frame is level there is a gap from the floor (not completely installed yet) and mount. Not sure how critical it needs to be for the sub frame to be completely level other then fit up of the body panels Attachment 626518Attachment 626519Attachment 626520Attachment 626521

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Yes new floor with braces already attached. Unknown subframe but not first gen. Could only bolt up subframe to body at most aft position. Meaning I could not align frame with alignment holes on firewall. I figured easiest thing to do is just move the captive nut forward 1/2 in and call it a day

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I will toss this here, hope it makes sense.
https://forums.maxperformanceinc.com...1&d=1705597384

Yes thank you! Exactly what I needed. Ok I confirm then I have the right subframe. the measurements H are good per the fisher book. What I don't have are the measurements from the forward rear guage hole to where the frame bolts in. However even if it's off is it worth it to move both braces forward 1/2 in, then simply my approach to just move up the captive nuts? Attachment 626811Attachment 626812

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Subframe, All years Firebird bolts in the front of car to the Torque Boxes.. one side has an alignment hole to allow frame to pivot while doing the keystone adjustment. Nothing bolts in the rear torque boxexcepr spring buckets