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Does anyone know what the "hash marks" are at 10 & 15, 35 & 40 and 72.5 & 77.5 mph? They are on all 1980 - 1986 speedometers, regardless of engine, transmission and differential variables.
I borrowed this picture from Gary Lewis's thread about speedometers.
Does anyone know what the "hash marks" are at 0, 10 & 20, 30, 40, 50,60,70 & 80 mph? They are on all 1980 - 1986 speedometers, regardless of engine, transmission and differential variables.
The "hash marks" are used in lieu of numbers (MPH: 0 - 10 - 20 - 30 - 40 and etc.).
Thanks, Mr. NumberDummy, but I was referencing the vertical ones at 10 and 15 mph & 72.5 and 77.5 mph as well as the horizontal ones at 35 and 40 mph [just under the odometer].
Thanks, Mr. NumberDummy, but I was referencing the vertical ones at 10 and 15 mph & 72.5 and 77.5 mph as well as the horizontal ones at 35 and 40 mph [just under the odometer].
Just for clarity, these are the marks in question.
I think each pair is an engine rev limit for each gear. On my '84 (351W, T-18 4 speed, 3.54 diffs), when the needle is centered between each pair, the engine RPM was a certain speed. The first pair is for 1st gear, and so on. Working from memory, I think it was around 5000 RPM. Never had my engine up to that speed, don't ever plan to. I calculated where the speedometer needle would be at 5000 RPM by doubling the speed shown at 2500 RPM.
No idea how or why all models have the same marks. Perhaps it was a feature that wasn't fully implemented across all transmission and diff gearing combinations, but they never bothered deleting the hash marks. That might explain why there doesn't appear to be any official documentation explaining their purpose.
Sorry, but I can't see that working since there were axle ratios from 2.72 to 4.56, and transmissions with a top gear of .67 to 1.00 plus slippage. So, a truck with a C6 and a 4.56 axle would have the engine turning over 2.5 times as fast as a truck w/a 2.72 gear and an AOD. And those hash marks aren't nearly that far apart.
There is a special explanation for these marks. First, you can see that at the lower speed the dashes are longer. I can only assume that they get shorter the faster you go because they represent the length of your life expectancy when driving these trucks at that speed.
Otherwise I would suspect it has something to do with AOD only as the engineers that built that transmission were a little wacky.
There is a special explanation for these marks. First, you can see that at the lower speed the dashes are longer. I can only assume that they get shorter the faster you go because they represent the length of your life expectancy when driving these trucks at that speed.
Otherwise I would suspect it has something to do with AOD only as the engineers that built that transmission were a little wacky.
Sorry, but I can't see that working since there were axle ratios from 2.72 to 4.56, and transmissions with a top gear of .67 to 1.00 plus slippage. So, a truck with a C6 and a 4.56 axle would have the engine turning over 2.5 times as fast as a truck w/a 2.72 gear and an AOD. And those hash marks aren't nearly that far apart.
Gary, I probably didn't explain my crackpot theory well enough.
First, notice that each pair is almost perfectly one needle width apart. I think the gap even varies slightly to compensate for the taper of the needle rotating inside a squarish scale. You gotta give me that one. It sure seems each pair was made to bracket the needle.
Second, my hunch was the bean counters got involved late in this design and put the kabosh on it. I fully agree each transmission and diff combo would need its own specific speedometer face. I also suspect this max engine RPM display was only for manual transmissions, as autos would theoretically shift on their own before overspeeding the engine.
So in my imaginary little world, the many different speedometer faces were prepared for production. At some point, accounting stepped in and said they couldn't authorize this extra expense and complexity on the assembly line. Who knows, maybe they gave the order to leave the tooling as is, and use up what had already been produced, which just so happened to be the marks required for my truck.
Meanwhile, since this feature wasn't going to be officially incorporated after all, any reference were scrubbed from the owner's manual, service manual, etc. (It's sorta like how Subway has erased all references to Jared Fogle.) Ford just didn't spend the extra money to change the tooling, thinking few people would ever notice.
Gary, I probably didn't explain my crackpot theory well enough.
First, notice that each pair is almost perfectly one needle width apart. I think the gap even varies slightly to compensate for the taper of the needle spinning inside a squarish scale. You gotta give me that one. It sure seems each pair was made to bracket the needle.
Second, my hunch was the bean counters got involved late in this design and put the kabosh on it. I fully agree each transmission and diff combo would need its own specific speedometer face. I also suspect this max engine RPM display was only for manual transmissions, as autos would theoretically shift on their own before overspeeding the engine.
So in my imaginary little world, the many different speedometer faces were prepared for production. At some point, accounting stepped in and said they couldn't authorize this extra expense and complexity on the assembly line. Who knows, maybe they gave the order to leave the tooling as is, and use up what had already been produced, which just so happened to be the marks required for my truck.
Meanwhile, since this feature wasn't going to be officially incorporated after all, any reference were scrubbed from the owner's manual, service manual, etc. (It's sorta like how Subway has erased all references to Jared Fogle.) Ford just didn't spend the extra money to change the tooling, thinking few people would ever notice.
That's my story and I'm sticking to it...
That makes sense. Thanks for explaining - I'm slow.
What if they are quick reference points for checking the calibration from the factory where the speedos were built? +-2 to 3 mph. It would make sense that there are three points of reference, low, med, high speed.
Most older vehicles I've had, the speedos were 2-3 off. The newer vehicles seem to be closer.
It sure seems each pair was made to bracket the needle. 