Why do antique auto tachs do this?
 

I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric

Why do antique auto tachs do this?
 

On Monday, January 30, 2017 at 6:00:50 PM UTC-5, wrote:
I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric

I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.

I started sports car racing in 1966, and my first tach was a Sun Tach that was all-electronic and very smooth -- aftermarket, on my John Fitch Corvair.

--
Ed Huntress

Why do antique auto tachs do this?
 

On Mon, 30 Jan 2017 15:12:29 -0800 (PST), wrote:

On Monday, January 30, 2017 at 6:00:50 PM UTC-5, wrote:
I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric

I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.

I started sports car racing in 1966, and my first tach was a Sun Tach that was all-electronic and very smooth -- aftermarket, on my John Fitch Corvair.
Maybe that's why the motion isn't smooth, there is some stiction maybe
going on.
Thanks,
Eric

Why do antique auto tachs do this?
 

On Mon, 30 Jan 2017 15:05:47 -0800, wrote:

I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric

I believe that you are talking about a Cronometric tachometer. Smith's
cronometric speedometers and tachometers were common on both
automobiles and motorcycles at one time.
See http://tinyurl.com/h6n8m47 for some details.
--
Cheers,

John B.

Why do antique auto tachs do this?
 

On 1/30/2017 6:12 PM, wrote:
I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.
...

3:16 here https://www.youtube.com/watch?v=VMP7fW7tj3w

Why do antique auto tachs do this?
 

On Tuesday, January 31, 2017 at 1:08:32 AM UTC-5, Bob Engelhardt wrote:
On 1/30/2017 6:12 PM, wrote:
I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.
...

3:16 here https://www.youtube.com/watch?v=VMP7fW7tj3w

Oh, man, what a cool car. I don't know how that one passed me by -- or maybe it didn't and I just forgot about it. In 1966, the only things I cared about were girls and sports car racing.

Thanks, Bob.

--
Ed Huntress

Why do antique auto tachs do this?
 

On Tuesday, January 31, 2017 at 1:08:32 AM UTC-5, Bob Engelhardt wrote:
On 1/30/2017 6:12 PM, wrote:
I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.
...

3:16 here https://www.youtube.com/watch?v=VMP7fW7tj3w

BTW, I caught that jerking tach. I just got caught up in the car. g

--
Ed Huntress

Why do antique auto tachs do this?
 

On Tue, 31 Jan 2017 08:45:10 +0700, John B.
wrote:

On Mon, 30 Jan 2017 15:05:47 -0800, wrote:

I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric

I believe that you are talking about a Cronometric tachometer. Smith's
cronometric speedometers and tachometers were common on both
automobiles and motorcycles at one time.
See http://tinyurl.com/h6n8m47 for some details.
Greetings John,
That's it! Thanks! I went to that site already but only saw the eddy
current type. It has bugged me for a long time why the jerky motion
tachs were used and no I know. Cool.
Thanks again,
Eric

Why do antique auto tachs do this?
 

On 1/31/2017 1:22 AM, wrote:

BTW, I caught that jerking tach. I just got caught up in the car. g


Ha! Me too - I went to YouTube for the "Victory By Design" that Eric
referenced, saw the Jag, and got lost down a rabbit hole. Like you, I
don't know how I missed that back in '66, but career had displaced cars,
I guess.

Why do antique auto tachs do this?
 

On Wednesday, February 1, 2017 at 9:56:23 AM UTC-5, Bob Engelhardt wrote:
On 1/31/2017 1:22 AM, wrote:

BTW, I caught that jerking tach. I just got caught up in the car. g


Ha! Me too - I went to YouTube for the "Victory By Design" that Eric
referenced, saw the Jag, and got lost down a rabbit hole. Like you, I
don't know how I missed that back in '66, but career had displaced cars,
I guess.

I'm glad that Eric didn't get us started on that series before I retired, or during trout season. I know now where I'm going to be spending some spare time this month. Many of those are cars I've always loved and those videos get my heart racing.

--
Ed Huntress

Why do antique auto tachs do this?
 

On 01/30/2017 06:12 PM, wrote:
On Monday, January 30, 2017 at 6:00:50 PM UTC-5, wrote:
I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric

I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.

I started sports car racing in 1966, and my first tach was a Sun Tach that was all-electronic and very smooth -- aftermarket, on my John Fitch Corvair.

The OP is describing a chronometric tachometer. I had a Royal Enfield
and an Atlas that had them.
http://www.mg-tc.de/articles/JaegerC...struments.html
http://www.chronometrics.co.uk/Tacho...chometers.html