Speedometer observation/question?
 

I know this forum is for engines, and if the Moderator thinks should be deleted, I do understand and will not be offended.

I am attaching a link to the 1980 - 1986 Bullnose forum and hoping that some of you, who do not frequent the other forum, can help figure this out. https://www.ford-trucks.com/forums/1...l#post18034695

Thanks!

No worries.


Interesting, I've never noticed those before!

And I honestly have no clue what they're for. Your speculation about calibration is as good as any.

Justin, if calibration, why not for the other 2 speedometers?

Good question. If that's what it was for, you'd think it'd be on all of them.

I was wondering if it was design, but they're not symmetrical.
They're also not popular speed limits. Was doing some google searches about marks on speedometers and that's what most of them were for (like our line around the 55 mark).

I also wondered if, since they're in pairs, there's something between them (like if you center between the last two, you're at 75), but the first two would be something like 12.5 and 37.5.

Lastly, they're not right on the lines, or directly between them.

If you look closely, (and going by the 'left' side) they look like they're about: 7.5mph, 14mph, 34.5, 40.5, 72.5, 78.


Now I'm really curious, too.

Yep! I've been thinking about this all day since reading it over in the bullnose forum...

My first thought is, if used during development for some sort of calibration - it seems foolish for Ford to put these marks into production vs. having temporary marks only for the calibration vehicles. This leads me to believe that these marks serve a purpose "after the production line".

My second thought was, "maybe it was used by local regulations authorities during inspections to test speedometer accuracy against applicable laws". I thought this might be the reason why it does not appear on the "metric" version (regulations are different where metric is used). But after reading, the laws state that it must be accurate within +/- 5 mph at 50 mph, so the placement of the marks you showed make no sense (unless the regulations were different back then). Also, if this were true - other manufacturers would do the same (I would assume). I did an image search and did not find similar marks on speedometers from other manufacturers during those years.

I also tried to think of any manufacturing reasons (ejector pins from the plastic injection molding process), but the placement doesn't really make sense for this.

Shift points might have made sense for a particular drivetrain combination, except for the 75 mph marks... that's a pretty high speed for a shift point!

The problem for me is, there must be a logical reason. And if we knew it, we would all collectively say "OHHHH, well THAT makes sense" - but I think we need to find a development engineer for clusters at Ford from that period to find the reason haha

I'll keep my thinking cap on for a while longer :-X20