Speedo gear -21 or 22 tooth sets available?

[taijirich]

Thanks, it seems that I can only go up two teeth with the available gears(the biggest gear I can find is a 21 tooth) The math that you mentioned gives me 22.8 teeth (20% increase from 19 tooth gear). Other sites mention that Ford and GM are calculated by a rough percentage by tooth. That is what I am trying to determine.

 

[Crashtd420]

I'm not sure if its available anymore, I'll have to check,  but about 5 years ago I got a metric ratio adapter....

I drove 10 miles based on highway markers and noted the mileage of the odometer... they had a big chart to calculate the difference..... 

[datzenmike]

17 hours ago, taijirich said:

Hopefully, nobody gets too upset with me reviving this old thread, but this is the closest that I have come to finding out exactly what I need. I have a 1983 280zx GL that I am in the process of modifying. I bought the Autometer Ultralight set of gauges from the Z store and had them installed, they look great, but the speedometer is not even close to calibrated. I understand that mechanical speedometers will only be accurate at one speed, and will be over below that speed, and under above that speed. Mine says 120 mph but according to GPS is only going 100 mph. Everything is stock, so I should have the white 19-tooth pinion gear. I would like to be as close to accurate as possible at 60 mph. From reading this thread, it seems like the purple 21-tooth gear might be right, but would the orange 22-tooth be better?

 

15 hours ago, shaddai said:

No. Mechanical speedos will be fine across the whole band. It's the ratio that people often miscalculate ("my Speedo is 5 mph fast", no it's not, unless it says 5mph at 0mph and 55 at 50). You are 20% high, so you want to go ~20% bigger. It's not exact depending on bigger vs smaller. I'm too tired to do the math properly at this exact moment, but don't assume what you have. Go check (and then refill your transmission oil). Then do the math.

 

It's a percentage out. If you say 5 mph out that's meaningless unless the speed is also quoted. If 5% out at 100 MPH then it's only 2.5MPH out at 50 MPH and 1.25  out at 25 MPH. All of these are still 5% out.

 

If reading 120 but actually going 100 then you are 20% FAST and the speedometer cable needs to slow down by 20 %. Take the speedometer pinion out and see it what you have. It may simply be a swapped transmission from a truck and too small a diameter tire. Find out.

 

Assuming that it actually IS a 19 tooth, then more teeth will take longer to be turned and will slow the cable down. 19 X 1.2 is exactly 22.8 teeth and would be perfect, but that's impossible, so a 23 tooth would be the closest and be just 1.05 MPH out at 100 MPH and 0.5 MPH at 50 MPH.

 

If only a 22 tooth is available then you will still be fast but reduced to 4.3 @ 100 MPH and 2.15 MPH at 50 MPH.

 

 

Obviously you can only cram so many teeth on a pinion gear before the diameter becomes so large that the plastic gear is crushed against the worm gear in the transmission. To avoid this Nissan provides several different off sets in the metal sleeve that holds the gear. Generally one of these sleeves can accommodate a range of, I think, 3 pinions before the gear is either crushed or is not held close enough for the gear to engage the worm gear on the output shaft of the transmission. For example a 16, 17 and 18 tooth pinion can share the same sleeve but a 19 tooth would be too large a diameter. 19, 20 and 21 on a different sleeve and so on. I have no idea if a 23 or even a 22 tooth will fit your 19 tooth sleeve, probably not, so if you find a 23 try to get the sleeve with it.

 

 

 

 

I needed an Orange 22 tooth for my 710 with a 4:11 differential and whatever tires I had. I even tried 'gluing' two 11 tooth parts together but when I drove the teeth were crushed because the sleeve was for a Purple 21 tooth and it was maxed out. Charlie 69 had an orange 22 tooth and sleeve and now the speedometer is perfect.

 

 

 

 

 

[taijirich]

so, I found this one. Would this fit? https://www.ebay.com/itm/155315150969


I have yet to find a 23-tooth.  I found another thread last night saying that 5.555 % change per tooth... that changes the number just a bit to a 22.6-tooth vs. 22.8. can anyone confirm if is a straight ratio or 5.55% per tooth?

[shaddai]

28 minutes ago, taijirich said:

so, I found this one. Would this fit? https://www.ebay.com/itm/155315150969


I have yet to find a 23-tooth.  I found another thread last night saying that 5.555 % change per tooth... that changes the number just a bit to a 22.6-tooth vs. 22.8. can anyone confirm if is a straight ratio or 5.55% per tooth?

Math is hard*

 

You get diminishing returns with tooth count increasing. Think of it this way... if you had 1 tooth, going from 1 to 2 would be cutting the rotation by 50%. But from 100 to 101 is only 1%. So the effective difference between 16 and 17 is greater than 21 and 22, albeit less extreme than my example.

[shaddai]

1 minute ago, shaddai said:

Math is hard*

 

You get diminishing returns with tooth count increasing. Think of it this way... if you had 1 tooth, going from 1 to 2 would be cutting the rotation by 50%. But from 100 to 101 is only 1%. So the effective difference between 16 and 17 is greater than 21 and 22, albeit less extreme than my example.

Also... if you've truly checked the math and found exactly what tooth count you have today, here's a link to what should be a 23 tooth assembly.

 

https://www.megazip.net/zapchasti-dlya/nissan/pinion-assy-speedometer-3270258S23?q=32702-58s23

[taijirich]

23 hours ago, shaddai said:

Math is hard*

 

You get diminishing returns with tooth count increasing. Think of it this way... if you had 1 tooth, going from 1 to 2 would be cutting the rotation by 50%. But from 100 to 101 is only 1%. So the effective difference between 16 and 17 is greater than 21 and 22, albeit less extreme than my example.

ok, now this makes the most sense that I have found. Thanks, I can do the math, I was not looking at it as a straight math computation.

[DARIN 510]

What rear diff do you have? Stock ?

[datzenmike]

The gears available are roughly 15 to 23... may be more but this is close. The % change is very roughly 5% between adjacent numbers. For example 16/15=6.666% but 23/22=4.54%.

 

You need to know how much faster or slower you are going at 100 mph. This gives a % error. You can to this at 50mph and double to get difference at 100mph. You can also use your odometer but you need as large a number as possible and on a highway with mile markers. (GPS might work also) 

 

Lets say that you actually go 55 miles but read 50 on odometer. That's 10% fast so the speedometer cable needs to slow by that amount. You check and have a 19 tooth gear in the transmission. A 21 tooth divided by your 19 tooth is 10.5% slower. So close to your target of 10% that you won't notice that 1/2%. That's 1/2MPH at 100 or 1/4MPH at 50 PH. Usually the error of larger tires isn't significant and the most needed is one tooth but changing differentials is much more....

 

You had 3.70 differential but swapped in a 4.11. 4.11 divides by 3.7 is 11.08% faster spinning cable. If you had a 17 tooth gear then a 19 tooth is 19/17=11.76% as close as you are likely to get.

 

 

 

Purple is 21 tooth. This was as close as I could find until Charley69  was gracious enough to send me an orange 22 tooth pinion. This was a change from 3.70 to 4.11 differential and the tires were not exactly stock so it was a perfect fix. Speedometer is now so close you can't tell.