Speedometer Gear Assistance Needed

[datzenmike]

I'm experiencing a similar issue. At 60, the speedo reads 80. At 30, the speedo reads 40.  Seems like it reads 33% higher than it actually is.. pretty sure it's the later style ZX 5spd, because the 5th gear is really tall. It's with a 3.70:1 rear end, I believe..(whatever was in the 69' 510 4spd). Would this be correctable by installing the pinion from the 4spd into the 5spd?.. or am I missing something..

 

The plastic pinion gear is mated to the differential ratio. If you ever get a different diff gear set, always get the pinion out of the tranny. When you swap it in, swap in the pinion and the speedo will always be correct. (this assumes the transmissions are the same and the pinion sleeves compatible) Once you have the correct pinion gear to match the differential, the transmission gearing and overdrive matters not. The pinion is telling the speedometer how fast the diff (or wheels) are turning, not the overdrive revs of the motor.

[MicroMachinery]

White gear. 19 teeth

[datzenmike]

So if you can find a 21 tooth that's about 10% improvement.

 

I think there is a 22 tooth in the D-21 but may not fit your trans.

 

What trans are you running micro?

[MicroMachinery]

I thought it was from a ZX, but after getting under I'm not sure.. I'll go look for numbers.

[ggzilla]

You must be running really short wall tires to be that far off. I'll bet the speedometer head is 15% off too.

[datzenmike]

Micro, it's easier to tell if it isn't a zx. Look for the speedometer cable and follow back to the speedometer pinion sleeve. If the 10mm mounting bolt is on top (12 o'clock) it isn't. If at 6 o'clock it probably is but could also be from an '80 720 or Maxima.

 

Not a zx

 

 

Might be a zx

[MicroMachinery]

6 o'clock. Interesting.. I pulled a pinion from a known ZX trans, as well as a 510 trans, and they are both steel bodied. The one in the mystery 5 speed is aluminum, but the same length as the ZX one. The 510 one is the tallest.

[MicroMachinery]

Also, both the ZX and 510 gears are 16 tooth, as well as yellow.

[MicroMachinery]

I just pulled a red 20 tooth from a 620 4spd trans, but the diameter is larger.. probably wouldn't work, eh?

[ggzilla]

Probably would work, for a short time.

[MicroMachinery]

You must be running really short wall tires to be that far off. I'll bet the speedometer head is 15% off too.

Not sure. I replaced the gauge cluster and it's the same. The tires are 175/70/13

[ggzilla]

Maybe you ran over a possum and knocked the speedometer out of calibration ? Oh wait ...

[MicroMachinery]

Must be jrock you're thinking of..

 

 

[datzenmike]

You can swap the RED pinion gear but the sleeves prior to '80 will not swap with those '80 and on. That's why the bolt moved from 12 to 6 o'clock. To fit the 620 sleeve simply cut a new notch 180 around so the 6 o'clock bolt and key will work. I've done this on my 710 5 speed.

 

 

Not mine, but I did use an angle grinder to cut the notch.

[Dzaster]

At 55mph on GPS my speedo shows roughly 65mph. I believe my pinion is BLUE, 18T (see pics below)--kinda looks turquoise but my blues and greens perception is off.

 

 

 

If I'm understanding correctly, switching out to the a RED, 20T gear pinion should bring me closer to actual speed. Also I need the appropriate sleeve for 20T as the 18T sleeve is different?

 

If I'm correct, anybody have 20T with matching body they want to sell or trade for my 18T?

[datzenmike]

A combination of things may be in play here. Differential was swapped to something lower numerically like a 3.545 as well as taller tires. The transmission may have been swapped in that has a lower tooth count.

 

10MPH out at 55 is close to 20% error. Just how accurate is a GPS anyway???

 

I would start by following someone with an accurate speedo or time yourself on a highway with mile posts. 60MPH is one mile per minute so 50MPH would be 72 seconds... one minute and 12 seconds. A 50MPH reading will be easier to figure the error in %

[ggzilla]

GPS is accurate to 20ns, better than any consumer clock. Location accuracy is 95%.

 

You should start with Odometer check and gear for that. Then adjust speedometer drive cup drag if still off.

[DanielC]

I have been using a GPS handheld device to check analog speedometers in my boat, for a few years now.  Boats are also using GPS for speedometers.

There are two ways a GPS speedometer works.  One way, it gets a fix, or marks a location, then gets another fix, and measures the distance between the two points, and the time it took to move the distance, and calculates the speed.  this can onl happen as fas as it gets a fix.  When accelerating, it will not read true speed, it will read the speed the last time it got a fix on a point.  It you are going around a circle, it also does not know that, and you get the speed based on the straight line distance.

If you are going relatively slow, the inaccuracy built in to the GPS will also alter the speed reading. 

 

The second way GPS speedometers get speed is by using Doppler shift of the radio frequency coming from one satellite.  You have to be moving closer, or farther away from the satellite for this to work.  A satellite straight overhead will not work, your distance to that satellite is not changing.  This is also true of any satellites directly to the right or left of you.  To use a satellite for Doppler shift, it need to be low on the horizon, directly in front, or behind you.

 

To avoid GPS errors when checking speed, you need to be going in a straight line, at a constant speed.   Then you can use it.

 

But before you change the speedometer pinion in the transmission to correct the speedometer, you need to make sure the odometer is reading off, too.  The odometer had a direct mechanical geared connection to the rear wheels.  The speedometer is just a spinning magnet, in an aluminium cup, being dragged higher, against a spring, by inducted magnetic forces.

[Ron1200]

Adding some info from G-Duax on Speedo part numbers

 

Here is the info I've found on all the gears, many are not available any longer:

 

  Nissan Pt #     #T     Color    Ratio   Gears

 

  32703-78100   16T (yellow)  3.364   37/11

  32703-78101   17T (black)    3.545   39/11

  32703-78102   18T (blue)     3.700   37/10

  32703-78103   19T (white)   3.900   39/10

  32703-78104   20T (red)      4.111    37/9

  32703-86401   21T (purple)  4.375   35/8

  32703-86402   22T (orange) 4.625   37/8  (32703-P2622)

  32703-86403   23T (green)   4.875   39/8

 

  32707-7800 16-19t Sleeve Assy

  3270766300 20-23t Sleeve Assy  (

 

The 20-23T sleeve PN (32707-66300) has an alternate 32707-P3620 or 32707-C8301
 

22 & 23t gears - 32703-86402 or 32703-86403. (gear only)

32702-52L21  is assembly (22t)

[datzenmike]

Would love an Orange pinion gear.

 

 

Keep in mind that the differential gear ratios are approximate.  A 510 with a 3.70 and a 23" diameter tire is not going to be correct for a 720 with a 29" diameter tire and a 3.90 differential.

[HRH]

Last I checked, I ran all the numbers at Jaremko and none were available any longer.  Pretty much just programmable speedometer, shell out the bucks.

[datzenmike]

Yeah, so if you ever come across them, save them.