How to design and build a frame jig in only 6 months!
Remember The Damage? It's time to start having hard conversations with ourselves. Specifically, how is someone (me) who has only done brake jobs, oil changes, and water pump replacements going to remove and replace an entire structural chunk of a classic American car without making a total shambles of it all? We're talking about pulling parts off the car that were really never supposed to come off - ever - and put them back exactly where they are supposed to be.
I need to put a new one of these on the car:
No worries, I have an actual Ford Shop manual for my car. There's whole paragraphs on how the power steering control valve works. There's gotta be pages on this. I'll just open it up the manual and see what it can tell me...
And, no kidding, this is all that's in the manual. One drawing. This, on its own, is not very helpful to me. Right off the bat I'm sure I don't know enough about this.
So after a LOT of research, reading, pondering, and sketching ideas on napkins, I finally feel comfortable enough to give this a go. All told, I thought about this part of the project for about a year as I was doing other stuff. Again, I'm slow, I know.
Here's the deal: in order to do this sort of work, one needs to build or acquire a body jig to hold and stabilize the car, then place the car on said jig so that the only parts that move are the parts that are being removed and replaced. The big questions here are:
- what kind of jig? (body cart, fixed-base, or - my favorite - custom hack job)
- where to attach the jig to the car? (hint: not to parts that are going to be replaced)
- what should it be made of? (hint: not bricks or jack stands)
- what sort of music should one listen to while building a jig? (this one's a no-brainer: Will Smiths 1997 hit "Gettin' Jiggy With It" - lyrics [by Nas, who knew?] are interjected at appropriate points in the text.)
- fore-aft position,
- the left-right position,
- the height off the datum plane
- pitch, and
I built the jig under the car to my specs and then lowered the car onto it. I used a laser level to make sure I get the jig's datum plane level.
Details on Frame measurements used for the jig:
As mentioned above, I had to hunt and scrounge the web for measurements I could call 'real'. In the end I used the 67-68 frame drawing in the back of the manual (shown here), as well as some measurements from the 69-70 frame drawing. As it happens the front end between these two generations is pretty much the same, so a dimension on the 69-70 drawing will work on a 67 chassis. But I had to do a lot of research to figure out which would work.
Additionally, and you have to be careful here, some measurements come from real restorers posting measurements online taken off good cars. This is tricky because you have to know the source is really good enough to use - this is hard on the interweb.
So, here's what I used:
From the 67-68 Shop Manual Frame Drawing :
- Red boxes indicate actual frame dimensions used (6).
- Blue line indicates measurement between frame rails just above the forward edge of the floor supports (27.62", ±0.125", from here). The relative location is the blue dot on the side view.
- Yellow line indicates the measurement between the rear aprons at the top where the hood hinges bolt on (40.0", ±0.25, from same link as #2 - good thread, and Rusty428CJ is one of those trusted sources.)
- The green lines are the diagonals from rear floor support hole to front frame rail forward hole, projected down on a parallel plane (like all plan view dimensions). Basic geometry and the assumption that the angle drawn from between the two holes at the rear of the floor support (29.88") forms a right angle with the line that is measured (as in, not shown here) from rear hole to forward hole. These two diagonals need to match. With my bent frame rail, they didn't. Good dimension on my car (70.00") was measured at hole edges. Your mileage may vary.
- LCA mount, Left to Right (19.125")
- Forward frame hole, Left to Right (30.00")
One last piece of advice: measure it all one more time.
Good luck - hope this helps.