Chassis Dimension Questions

[basstrix]

My first question is, what manual(s) are these two images from? I have the Weld/Sealant and Body Assembly and they are not in those manuals.

Second question is regarding discrepancies between the two diagrams.

Datum Line: Both images have 12-3/8 at the front but use different references. At the rear, they use the same reference but the dims are substantially different. Both images imply the center portion of underbody is parallel to the datum line. It's possible the values are accurate but the parallelism of underbody to datum not correct.

Some of the dims match up (highlighted in green).

Have both of these diagrams been verified to be correct?

 

[judge]

The top chart comes from the shop manual for that car. The lower drawing appears to be put together after the fact. There may be some way that there both correct. I'd use the shop manual.

 

[Qcode351mach]

The lower drawing is one I got from a older frame dimension book usually supplied by frame machine manufacturers. It was in a bunch of frame charts being thrown out at a body shop I worked at. I had given to a few members here who then posted.

The difference your seeing on the datum line is just the HEIGHT that the gauges or measuring system would be set at those points in order to establish a line for all the other measurements to be taken from (datum line) OR where you set the chassis in relation to the flat plane of the frame machine, depends what frame machine or measuring system your using

As a example I could hang or set a pointer at those control points I then string a line from point to point that is the datum line in RELATION TO THE CHASSIS...so doesn't matter if I use 6" as a control point or 8" as long as I follow the chart.

I can verify that the lower chart is correct I have a non damaged 72 and have measured plus I used the lower chart on my other 72 when replacing the rear frame rails front rails shock towers and more.

 

[basstrix]

Q, thanks for the response. Since both diagrams are drawn to indicate the central part of unibody is parallel to the datum, I felt my question was warranted. I didn't want to invest a lot of time into using a known-erroneous chart. Of the two, I think the lower chart is more clearly drawn/written.

Thanks for confirming the lower chart is accurate.

 

[Qcode351mach]

Q, thanks for the response. Since both diagrams are drawn to indicate the central part of unibody is parallel to the datum, I felt my question was warranted. I didn't want to invest a lot of time into using a known-erroneous chart. Of the two, I think the lower chart is more clearly drawn/written.

Thanks for confirming the lower chart is accurate.

No problem the upper chart does have a few measurements the lower chart doesn't such as the mounting points of the upper control arms

If you look at this thread http://www.7173mustangs.com/thread-pics-pics-pics-410-of-them on my car you can see how I set up the car level on a dolly & then set up a measuring system using pointers..Theres one picture where you can see how important it is when doing structural work to use the chart. The prior shop had replaced the rear frame rails..they were installed a inch to high...

 

[basstrix]

Do you have a recommendation for a tram gauge on a budget?

 

[Qcode351mach]

Do you have a recommendation for a tram gauge on a budget?

I do,

I make my own depending on the length you need. I have some small ones using 2 arrow shafts that telescope into each other. drill a hole in each end--glue a small nail as a pointer in each end. I have longer ones that I made from a telescoping snow car scraper and one from a telescoping paint stick just use larger nails on those. I'm not at the shop but will see if I can post a pic in the next day or so

 

[Mister 4x4]

Q hooked me up with the bottom diagram so many years ago when I replaced the front clip on mine - it was a HUGE help in getting everything lined up and correct. ::thumb::

 

[basstrix]

Do you have a recommendation for a tram gauge on a budget?

I do,

I make my own depending on the length you need. I have some small ones using 2 arrow shafts that telescope into each other. drill a hole in each end--glue a small nail as a pointer in each end. I have longer ones that I made from a telescoping snow car scraper and one from a telescoping paint stick just use larger nails on those. I'm not at the shop but will see if I can post a pic in the next day or so

I found a youtube video and used some of his design and added a twist of my own...here's what I came up with:

 

[Qcode351mach]

I found a youtube video and used some of his design and added a twist of my own...here's what I came up with:

Looks good just be careful that it's strong enough and doesn't flex or move when fully extended. Most tram gauges are used for a point to point measurement so usually the ends are kept short or held at a very small fixed position.

Heres a great manual that may help you it's older but still very good for the basics. Actually that lower chart was based on using some of the systems in the chief manual

http://www.chiefautomotive.com/manuals/accessories/UGMS%20Users%20Manual.pdf

 

[basstrix]

Thanks for the link, looks like a good reference on how to make use of this thing.

Was checking some points under the hood last night and it seems a bit unwieldy with the adjustable pointers. I'm thinking I'll cut them down to 6" and use the remaining 12" pieces in case I need long pointers for something.