[Shiny]

Another rat-hole that I find interesting from a design/manufacturing perspective.

I started re-assembling my rear bumper and found a mismatch with the assembly drawing.

I have this reprint:



It shows the same PN 9428940 for parts 4 and 19. These are 7/16-14 dog point bolts.

Of interest to me is my car was assembled with two different bolt lengths, so obviously not the same PN as shown on the drawing.

Looking at the drawing, parts 4 and 19 both have revision notes. Unfortunately, I cannot read the notes on my crappy reprint.

Here's the two lengths on my car. One is 7/8, the other 1-1/4 from head to end of thread.



My speculation:

The factory and/or purchasing realized both locations could use the longer bolts without issue so they consolidated to simplify and revised the drawing. If true, then my car probably was assembled before all stock of the "shorter" bolts had been consumed. I would also guess the longer lengths were originally used between the brackets and the body (19) and the shorter between bumper and brackets (4).

This kind of stuff must drive you guys crazy if trying to accurately/concours restore a car.

Mike

[Shiny]

And another....

There are two 7/16" flat washers called out: designators 3 and 6.

3 - 9798965
6 - 531315

AMK says 531315 is thick (their B-11286), but all the washers in my car at the "6" location were thin.

In my car, thick washers were used at the "3" locations, where the brackets were clamped to the body with shims.

I'm putting it back the way I found it, but this feels like another mismatch between the hardware used by the factory to assemble my car and the drawing.

Then again, maybe somebody has been into this before and did whatever they felt like that day???

Mike

[Scarebird]

I ran into that sort of thing all the time researching brake conversions. Mopar was especially bad using multiple sizes differing little when one size would do the task fine.

I always thought that a good assembly engineer would design a setup that drunk idiots could assemble easily. Then we have the 1970-73 Firebird front bumper...

[Shiny]

Originally Posted by Scarebird

I ran into that sort of thing all the time researching brake conversions. Mopar was especially bad using multiple sizes differing little when one size would do the task fine.

I always thought that a good assembly engineer would design a setup that drunk idiots could assemble easily. Then we have the 1970-73 Firebird front bumper...

I never worked in automotive but respect what they accomplished and like to imagine their world. I really enjoy the manual drafting and hand-written revisions.

My guess: Some development/design engineer picked a short bolt because it was "right". It fit the assembly and saved money on the BOM cost. Then some manufacturing and/or quality engineer got tired of managing two part numbers and watching the line workers waste time sorting and getting told the bolts had been installed wrong. Then some purchasing guy negotiated a lower price on the long bolts by promising more volume to the supplier if the short one could be eliminated.

What I'm guessing didn't happen well was the manufacturing review of the new design. They probably didn't have time to deep dive every fastener and relied on early manufacturing experience to disclose issues and opportunities. The manufacturing team was probably under serious stress just to get a new design running at all. Once they saw the bolts were dog point where misalignment was probable, they may not have questioned the length. As you say, the line worker could get it done.

It's amazing in today's world to think they could ship a car that didn't 100% conform to a known design revision. Then again, vertical integration was pretty good at cutting corners and getting stuff done fast. A lot easier to have a revision discussion by walking to the line than hopping on a plane to visit an overseas supplier and dancing around proprietary information.

[dataway]

I think a lot of the specifications back then were more "suggestions" than rules

[Shiny]

Kind of like speed limits around here...