cudak888: 1971 M-code "Soylent Green" - 2024: Help me measure the frame!

cudak888 · Sep 8, 2024

It would help if I used the 1971 measurement - 12.38”. Apparently, the second of those two diagrams isn't from the '72 manual, but the '73, and the front bolt location reflects the lower hole designed for the 5mph urethane bumper brackets (for those who don't know what this looks like, there's a great picture in this thread, post #17).

However, like the idler measurement, It’s still ~1/4” too far forward.

I'll give the rest of the unibody another look over, but I can't imagine ~1/4" of length getting accordioned out of this car without the rocker panel or forward leaf spring eyelet area showing evidence of absolute annihilation.

-Kurt

cudak888 · Sep 8, 2024

There's one thing I wanted to ask, for assumptions are the spawn of many errors:

I've been assuming that the "A" in 7.58A, 11.15A, 22.86A, and 47.10A all refer to the frame measurements from a central point in the car that the engineers established as the "0" location. In doing so, I added 7.58" (A) and 66.86" for a total of 74.44" (189.07cm) from the forward leaf hanger eyelet ("rear spring front hanger hole in member") to the idler arm bracket lower mounting hole. It's reflected in the earlier photo I posted of the measuring tape.

(1973 shop manual shown w/correct rear framerail measurement, but lower 5-mph front bumper mount hole):

Is there any possibility that this is an incorrect assumption, and I've added length here?

Theoretically, if 7.58" is measured from this (apparently unmarked) zero point, then I can check this by taking 7.58", adding 20", and measuring from the idler to the master control hole ("M.C.H.") in the front framerail. If that checks out, the 55.30" diagonal should as well.

-Kurt

Sheriff41 · Sep 8, 2024

You're out of my area of expertise. I'm just going to follow along here and learn.

cudak888 · Sep 8, 2024

Sheriff41 said:
You're out of my area of expertise. I'm just going to follow along here and learn.

Look at it this way: We're part of the same club then - I've never done this before.

I'm just letting the factory dimensions, Q's recommendations, and logic guide me along the way.

If anything, the most important thing I've learned in this entire project (including the initial dive into it) is to listen to Q, keep an eye out, and if something doesn't make sense, stop and take a break - it helps to sit down, clear the mind, and then look again at the factory unibody dimensions.

Sweating one's butt off trying to make things fit under the car tends to play havoc with rational thinking; the front bumper hole was a perfect example. It took a break and a few hours of unrelated tinkering to note the really obvious mistake that "1972" shop manual is actually the 1973 manual. Had I realized it from the start, I would have probably scrutinized the front bumper mounting hole measurement immediately. Instead, it took some clear-mind Googling until I wound up back in this thread looking at the two diagrams and realized the error.

It would be easy to say that everything is "good enough" at this point and weld in the right rail to where the left one is now, but it wouldn't necessarily explain the trunk floor height discrepancy. Granted, if Q thinks otherwise, I might consider it, but I think the best thing right now is to verify the front measurements off the master control hole back. More data can't hurt.

-Kurt

ib4stangs · Sep 9, 2024

Is there anyone local with a "never hit" 71-72 you can measure the distances and verify? It would be nice if you could find one on a cart or rotisserie!

This link I found is a shot in the dark, but you never know where it might lead to...
https://www.ford.com/support/category/service-maintenance/collision-assistance/

cudak888 · Sep 9, 2024

ib4stangs said:
Is there anyone local with a "never hit" 71-72 you can measure the distances and verify? It would be nice if you could find one on a cart or rotisserie!

This link I found is a shot in the dark, but you never know where it might lead to...
https://www.ford.com/support/category/service-maintenance/collision-assistance/

Right now, my system can only measure with the right leaf spring and idler arm out of the car, so it would have to be on a cart or belly-down on the ground.

At present, I only know Big Blue, and that car has already seen a lot more Toby Halicki-levels of "action" than mine. There are a few others in town that I know of, but none in the right state at present.

Then again, I've been off the forum for years, so I'm going to run a Google search on it with "Miami" as a keyword (and hope I get Florida and not Ohio).

EDIT: Nothing on the forum. Also checked Craigslist, Facebook Marketplace, OfferUp - lots of lousy project cars, none of them in pieces. I swear there was a '73 Mach or Sportsroof a few months ago that was sitting on top of a container, but that listing has disappeared. Might not have been Miami either.

-Kurt

cudak888 · Sep 11, 2024

I fashioned a 90 degree tram gauge to measure from the very hole that Ford engineers dubbed the “Master Control Hole” (MCH) - part of the right front framerail that is very much a part of the right front frame horn - to the lower idler bolt hole.

Here, I didn’t focus as much on making it level, as the centering pin would allow me to pivot up and down on the MCH with minor variance.

The T-slot was configured to snake around the main jackstand:

Surprise…

Note the sweep of the witness mark?

A bit of fine-tuning led to this:

I think I have my answer.

Perhaps this is a quirk of the Metuchen production line? They made the ‘71 for such a short time that it might account for the lack of documentation online - though it's not as if the '71-73s flood search engine results to begin with.

There's also the possibility that my front framerails are welded 1/4” closer to the firewall than usual.

Then there's the possibility that every ‘71-73 may reflect this, and the factory chart is, in fact, off.

IDEA: If anyone on the forum with a '71-73 on a rotisserie is game (and has nothing else better to do), I could ship out this shorter piece of T-slot around, set to the proper measurements. Thoughts? I'd love to get at least two other data points.

-Kurt

bishoppeak · Sep 12, 2024

MCH: Every wife has one of these!

cudak888 · Sep 12, 2024

bishoppeak said:
MCH: Every wife has one of these!

"Look out for the stick shift."

-Kurt

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