- Joined
- Jul 21, 2012
- Messages
- 3,280
- Reaction score
- 46
- Location
- South Florida
- My Car
- '71 Mustang Mach 1 M-code "Soylent Green"
'68 Plymouth Satellite
I'm currently sorting out a damaged rear framerail on my '71 Mach - the more in-depth details are in this thread.
In the process of doing so, I've set up a lightweight but serviceable jig to measure the hard points of the unibody, using modular aluminum T-slot (and speaker spikes threaded onto step-down studs fitted into the frame mounting points) to establish the baseline measurements per the factory service manual.
While I've since verified that the car is dead level side to side, it's slightly higher in front than in back, so I had to extend the T-slot to the lower idler arm hole and front bumper mount in the front of the car to establish at what angle the car is sitting relative to the ground. While the '73 front bumper location is different than '71, I've been relying on the 1973 manual for the most part, as it provides the horizontal distance of these hard points from front to back:
Everything was going as expected until I started verifying the measurement between the rear leaf spring hanger hole to the idler arm bracket and the front bumper arm. Both of these measurements are coming out about 1/4" further back than it should.
I know the car was hit twice in the back prior to my ownership - once fairly minor on the left side, once harder on the right side; it squished the rear crossmember and crumpled the quarter (since replaced). The only major damage was a small wrinkle on the framerail, just behind the axle bump stop. This wrinkle shortened the right side framerail by 3mm. That's it.
Now, for there to be 1/4" missing from between the forward leaf mount and the idler, there'd have to be one hell of a wrinkle in the rocker or somewhere nearby, and I can tell you for a fact that there isn't any. This car is outrageous in that it has nearly perfect original floorpans and torque boxes that have never been repaired (the car has been repainted once), and there's nothing anywhere on the whole car that indicates the hit ever traveled further than the framerail wrinkle. Plus, I've checked the forward leaf mounts with the T-slot and laser level and have found them to be square with each other.
In other words, I'm not really worried about further damage; everything points to the framerail wrinkle as being the only structural damage that remained (and since cut out waiting for its replacement section).
What I'm still trying to confirm = before I start tacking MIG welds - is the source of the current discrepancy at the idler hole.
A few days ago, I realized that I could use some of the T-slot to make a jig - essentially a slightly specialized tram gauge - to specifically measure the distance from the Master Control Hole in the left framerail extension to the lower idler arm hole, per the measurement from the manual: 7.58" + 20", center-to-center.
Guess what I discovered?
The same ~1/4" discrepancy showed up between these two holes.
I see no damage in front that would suggest it ever took a hit that would offset the right framerail this much, yet not touch the extension at all.
Just the same, I'm absolutely paranoid about getting this right and would like to verify it against two or three other cars.
If anyone is game - particularly anyone who has a never-crashed unibody disassembled and on stands - I'd like to ship this particular T-slot jig around to a few members willing to assemble it (the hard points will be tightened in place so you won't have to re-measure anything) and check it against their cars. I know this is over the top, but there aren't any disassembled '71-73s that I know of in town.
I'd particularly like to check this measurement against the following:
-Kurt
In the process of doing so, I've set up a lightweight but serviceable jig to measure the hard points of the unibody, using modular aluminum T-slot (and speaker spikes threaded onto step-down studs fitted into the frame mounting points) to establish the baseline measurements per the factory service manual.
While I've since verified that the car is dead level side to side, it's slightly higher in front than in back, so I had to extend the T-slot to the lower idler arm hole and front bumper mount in the front of the car to establish at what angle the car is sitting relative to the ground. While the '73 front bumper location is different than '71, I've been relying on the 1973 manual for the most part, as it provides the horizontal distance of these hard points from front to back:
Everything was going as expected until I started verifying the measurement between the rear leaf spring hanger hole to the idler arm bracket and the front bumper arm. Both of these measurements are coming out about 1/4" further back than it should.
I know the car was hit twice in the back prior to my ownership - once fairly minor on the left side, once harder on the right side; it squished the rear crossmember and crumpled the quarter (since replaced). The only major damage was a small wrinkle on the framerail, just behind the axle bump stop. This wrinkle shortened the right side framerail by 3mm. That's it.
Now, for there to be 1/4" missing from between the forward leaf mount and the idler, there'd have to be one hell of a wrinkle in the rocker or somewhere nearby, and I can tell you for a fact that there isn't any. This car is outrageous in that it has nearly perfect original floorpans and torque boxes that have never been repaired (the car has been repainted once), and there's nothing anywhere on the whole car that indicates the hit ever traveled further than the framerail wrinkle. Plus, I've checked the forward leaf mounts with the T-slot and laser level and have found them to be square with each other.
In other words, I'm not really worried about further damage; everything points to the framerail wrinkle as being the only structural damage that remained (and since cut out waiting for its replacement section).
What I'm still trying to confirm = before I start tacking MIG welds - is the source of the current discrepancy at the idler hole.
A few days ago, I realized that I could use some of the T-slot to make a jig - essentially a slightly specialized tram gauge - to specifically measure the distance from the Master Control Hole in the left framerail extension to the lower idler arm hole, per the measurement from the manual: 7.58" + 20", center-to-center.
Guess what I discovered?
The same ~1/4" discrepancy showed up between these two holes.
I see no damage in front that would suggest it ever took a hit that would offset the right framerail this much, yet not touch the extension at all.
Just the same, I'm absolutely paranoid about getting this right and would like to verify it against two or three other cars.
If anyone is game - particularly anyone who has a never-crashed unibody disassembled and on stands - I'd like to ship this particular T-slot jig around to a few members willing to assemble it (the hard points will be tightened in place so you won't have to re-measure anything) and check it against their cars. I know this is over the top, but there aren't any disassembled '71-73s that I know of in town.
I'd particularly like to check this measurement against the following:
- Any '71
- A '73, as perhaps this measurement changed between '71, 72 and/or '73
- At least one Metuchen car if possible, as mine is from that short production run that wrapped up before December 1970.
-Kurt
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