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Question about speedo gears and about snaps...

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amcboy

amcboy

Jedi Hopeful
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OK my speedo is off by about 5 MPH low across the board.

Are there drive gears available in other tooth counts. There are numerous choices for my 'merican cars.

I just need to drop a tooth or two...

Anybody know what tooth-counts were available? Where to get them? Haven't called TRF on this yet and would like to do so armed with some more info..


Also does anybody have an opinion (whoo, opened the flood gates there..) about plastic vs. metal snaps on the car body?

Especially reliability issues.

Thanks in advance!
 
amcboy said:
...Also does anybody have an opinion (whoo, opened the flood gates there..) about plastic vs. metal snaps on the car body?

Especially reliability issues.
Click to expand...
I've had very few problems with either, including metal female snaps on plastic male snaps, and vice versa. Ultimately, though, the metal ones are more durable.
 
I went with metal for reliability and because that's all that was available for a short period of time. I still would have done metal even if the plastic would have been available at the time.
 
Discovery on the subject of speedo gears:

Pre CF1 cars had 15 teeth, and late cars had 17 teeth.

Now, I wonder if the PI or KMh cars had a different count?
 
If the speedo error is linear (and you say it is) a simple reposition the needle' adjustment may be enough to give you reasonable accuracy. Described here:

https://home.comcast.net/~rhodes/

That is how I set mine, drive while the passenger holds a GPS, me calling out numbers and she taking notes. Pull into a parking lot, make a quick adjustment, try again. Fun, actually.

On the snaps -- metal is of course more durable -- I have heard some may be made of steel, you will want to get brass.
 
amcboy said:
Pre CF1 cars had 15 teeth, and late cars had 17 teeth.

Now, I wonder if the PI or KMh cars had a different count?
Click to expand...
I believe the later PI cars did have a different count (tho I don't have a parts book handy to check). That's because Triumph/Smiths changed their policy from a fixed 5:2 drive ratio (driveshaft to speedo cable) and different heads to account for different gear ratios, tires, etc.; to a policy of the head being a fixed 1000 turns per mile (even for KPH speedos) and the speedo drive gears being changed to suit. Since the PI models used 3.45 final drive gears, the speedo drive would also have been different.
 
Geo Hahn said:
If the speedo error is linear (and you say it is)
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Err, most people would say a "linear" error is one where the error varies linearly with speed, eg 5 mph high @ 30 mph and 10 mph high @ 60 mph, which cannot be fixed by moving the needle (except at one particular speed).

However, amcboy described a constant error, which as you say, can be fixed by moving the needle.
 
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