Know how to read GM instructions for bolt placement?

[71CHEVYSHORTBED402]

I honestly don't know how and that bugs me. I'd really like to know how. I'm no engineer, which goes w/o saying at this point. Never even assembled a model....ha!

First, are the measurements in inches or metric? If inches, 2.28 say what? (Slightly less than 2 9/32").

Second, where's the reference point? There may be one, but I'm not seeing it.

Third, I'd expect to see a measurement from the edge of the door. I don't see that either.


The first picture are the instructions.

The second is of a nice illustration for the passenger side. He says the penciled line is 1" below the door body line. That's confusing as well, as I'd expect that line to center between the two holes, though I don't have the hardware in front of me. I'm assuming mirror placement is square. It's my understanding the mirror on the driver's side would be 1.3" further forward.

The third is a nice illustration of the passenger side on.

[71CHEVYSHORTBED402]

If say .31 is decimal equal. of inches, I believe that's just under 5/16s. So I'm assuming if true, 2.31 would be a hair less than 2 5/16 inches.

[SS Tim]

Don't know how to start this but here goes.

The GM location measurements are presented in tenths/hundredths of an inch. They add up just like pennys, nickles and dimes. Might want to use a conversion chart in the back of the factory service manual to get you up to speed. 1/8 = 0.125, 1/4 = 0.250, 1/2 = 0.50 and so on.

The hole diameters are presented in fractions but most modern quality drill indexes are sorted by actual diameter or letter size. So if there is any doubt check it.

The actual referenced location points, like the "20" and the "35", are presented in a cartesian coordinate system from a fixed verticle reference point, a fixed horizontial reference and from the lateral centerline of the vehicle (in case you want to locate an antenne hole). These locations are used in production for uniformity. In this case 20 back and 35 up.

Unfortunately there is not an easy way to present that here.

There is a thread here on the board the has measured locations that IIRC LockDoc posted.

Try this search. Remember most of the time a site search based on how you would title a new thread will often have the answer waiting for you.

http://www.google.com/custom?domains...D%3A1%3B&hl=en


RTFM ... Read The Factory Manuals... download 'em here

[SS Tim]

If it makes it any easier the upper rear hole to the forward mounting hole is ~ 3-51/64", but 3.80" is so much more precise. The lower is ~ 3-49/64" or 3.77". If you are having a problem, it is fairly easy to find steel rules marked in tenths. Somewhere around here I even have a Stanley tape measure in tenths and MM! :-)

[71CHEVYSHORTBED402]

Thanks for the education Tim. I'm still digesting this. So in this example, 20 " back from? EDIT: SNAP!, must be the front of the outer cowl panel.

I figure I'll owe you a steak dinner of your choice when it's all said and done. You're quite a resource. Don't worry, not a "date"......ha!

Yeah, I was thinking I need the same measure.

[71CHEVYSHORTBED402]

Just bought the service manual. Already blew $1800 this week, what's another $26 at this point?...................Ha!

I think it's sunk in and I can read it now. Assuming the 20" is from the front of the cowl. Not sure where the 35" comes in, but I'll figure it out tomorrow..................Thanks

[SS Tim]

Very good grasshopper!
If you have your assembly manual yet the grids on the cabs and Blazers will help a lot with Cartesian prospective. Also if you have upper bodyside molding holes you can plot from a known 50 aft. Just read and understand carefully.
http://67-72chevytrucks.com/vboard/s...25&postcount=9

Totally Irrelevant info.....
You know this would be so much easier if you were using real mirrors, as in DF2s. They were dealer installed! :-)
http://67-72chevytrucks.com/vboard/s...6&postcount=10

[Shaky]

Originally Posted by 71CHEVYSHORTBED402

Thanks for the education Tim. I'm still digesting this. So in this example, 20 " back from? EDIT: SNAP!, must be the front of the outer cowl panel.

I figure I'll owe you a steak dinner of your choice when it's all said and done. You're quite a resource. Don't worry, not a "date"......ha!

Yeah, I was thinking I need the same measure.

Unfortunately, the numbers inside the circles may be GM's reference points from their fixture and not from the edge of the door. On aircraft blueprints the station, waterline, and buttline locations are difficult to reproduce unless you know the original reference planes.

I think your best bet would be to find some forum member here that has the same year truck and same mirrors and ask them to take some measurements from the edge of the door, body lines, etc...

[Lanman1972]

You can pickup a very inexpensive set of Digital Calipers that you can use for reference and layout of decimal locations. Also a Tap and Drill chart is a great tool to have on the wall and it will give you the decimal equivalents for your drill sizes. Hope this helps.

[71CHEVYSHORTBED402]

Originally Posted by SS Tim

Very good grasshopper!
If you have your assembly manual yet the grids on the cabs and Blazers will help a lot with Cartesian prospective. Also if you have upper bodyside molding holes you can plot from a known 50 aft. Just read and understand carefully.
http://67-72chevytrucks.com/vboard/s...25&postcount=9

Totally Irrelevant info.....
You know this would be so much easier if you were using real mirrors, as in DF2s. They were dealer installed! :-)
http://67-72chevytrucks.com/vboard/s...6&postcount=10

Those were the mirrors that came with the truck alright. I took them off decades ago, probably threw them away.

[71CHEVYSHORTBED402]

Originally Posted by Shaky

Unfortunately, the numbers inside the circles may be GM's reference points from their fixture and not from the edge of the door. On aircraft blueprints the station, waterline, and buttline locations are difficult to reproduce unless you know the original reference planes.

I think your best bet would be to find some forum member here that has the same year truck and same mirrors and ask them to take some measurements from the edge of the door, body lines, etc...

Agreed

[SS Tim]

All good points.

The station, waterline and buttline are referenced in inches from fixed datums. Like I said earlier its not an easy thing to explain. But it is very accurate as a 3d reference system.
As posted in 7 the 50 station/aft point is present on trucks with the upperbodyside/belt moldings.

There are decimal conversion charts (along with wire and sheetmetal gauge too) in the factory service manuals that are actually big enough to read. With the link provided it easy enough to download and print whatever you need.

I'm sure I've seen pictures of the base/sport mirror locations measured from the edge and bodyline in a thread here. So keep looking.