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Revision as of 05:59, 3 May 2009

Speedometers were either in kilometers (JDM) or miles (USA). Australia started with mph and then switched to kph. Some speedometers had a trip meter.

Comparo

1972 USA Owners manual (see page 8,9 for Speedometer):

Instrument and Controls

1 Variations
2 Metric-Imperial Conversion
3 Custom Faces
4 Speedometer Cable
- 4.1 Cable Breaks
5 Drive Ratios
- 5.1 Part Numbers
6 Photo Index

Variations

?? 100MPH w/o tripmeter (US standard equipment)
?? 100MPH with tripmeter
24850-H3400 1200 120MPH SPEEDOMETER Includes tripmeter
Facelift GX - 180 kph

Metric-Imperial Conversion

Sometimes on eBay Australia you can get the vintage conversion stickers.

Take the face plate and scan it on the flatbad scanner, then modify it. Finally, print a new one out with the photo printer. You can modify the font, colors, etc. Bolt it to the speedo using the standard screws.

Speedometer Calibration

There are two basic reasons for speedos reading fast or slow:

Factory speedometer tolerance is usually 5% fast to 10% slow (this is in general, I don't know what Nissan's specs are)
1200 Top Speed discusses this. One magazine test noted the 1200 speedometer in the test car was 7% slow. My 1200s have been between 7.5% - 10% slow (with stock running gear include tire size). Also see speedo off
Different size tires than original, changed diff ratio or transmission

For the latter, there is a mechanical solution of changing to the appropriate speedo-drive gear at the back of the transmission:

For the former, where you have the "right" size tires, final gear ratio and stock transmission -- the speedometer itself may be calibrated.

Mechanism Calibration

Where can you go to get a speedo calibrated? Can it be done at home?

MGA Guru: Speedometer calibration

You can:

Change the pointer position. This is good if the speedometer is off by say 2mph at all speeds.

Change the magnetic tension. This will adjust the scale across the board. Be careful as it is easy to ruin it
For ideas, see: Recalibration of Speedometer

Changing Scale

You can easily change the scale to make it read correctly, or to make a 180 kph scale. The downside is that the odometer (distance counter) will be inaccurate.

Scale Adjusted for low gearing, looks good printed on photo paper and bolted to speedometer.
Use a light, removable contact cement. Otherwise if you just tack the edges or a places, the photo will eventually buckle and warp and interfere with the needle movement.
I modified mine to change the scale since I didn't want to get under the car and change the plastic speedo gears.

Amplifier Speed Switch

USA model from 0772 use an amplifier speed switch.

25035-H7000 ASSY-AMPLIFIER SPEED SWITCH

Australia models also used it, dates unknown.

Custom Faces

See Custom Dash Faces

Speedometer Cable

The cable for manual transmission and Automatic are different

Rockauto.com $7.76

Nissan Part Numbers

B10

25058-89914 ASS'Y-SHAFT, flexible speedometer B10 M/T
25058-89915 ASS'Y-SHAFT, flexible speedometer B10 Automatic

B110 - both interchange

25058-H1000 ASS'Y-SHAFT, flexible speedometer Length=1500 NLA
25058-H1001 ASS'Y-SHAFT, flexible speedometer Length=1400 NLA

B210

25050-H5000 ASS'Y-SHAFT, flexible speedometer Length=1700
- B5050-Y8101 supercedes 25050-H5000 $51.22
25050-H5900 ASS'Y-SHAFT, flexible speedometer Length=1650 w/Master Vac NLA
25050-H7403 ASS'Y-SHAFT, flexible speedometer w/63-series trans
25050-H7410 ASS'Y-SHAFT, flexible speedometer A14 automatic
25050-H7411 ASS'Y-SHAFT, flexible speedometer A12

Cable Breaks

The speedometer cable usually lasts forever. There are two common reasons why it will break:

Mechanical kink or breakage, for example if you drive over a tree branch and it pulls the cable
Bad or missing engine ground wire.

I think you'll find this is caused by poor/dirty ground strap from the engine to the body inside the engine bay.
It only takes once, and the cable it screwed, as it melts the nice polyethylene coating on the inside.
See how the cable's protective plastic appear worn..I'd say it melted during starter crank. Then when the cable gets some speed up, the plastic grabs and the cable snaps.

Drive Ratios

Stock 1200 Speedometer gear ratio:

17/5 (17 tooth pinion, 5 tooth worm drive on trans output shaft)
18/5 for Wagon

To adjust the speedometer for different diameter tires, change the transmission cable pinion cog.

* If speedo reads too fast, fit a bigger cog
* If speedo reads too slow, fit a smaller cog

Given that stock is a 17 tooth pinion, moving to one more or less tooth is about 6% change. So by changing the pinion you can only get it to ±3 mph accurate. For example, at 100 mph, within 3 mph. Or at the standard 50 mph rating, a reading between 1½ mph (48½ to 51½) is the best you can hope for. For finer tuning the speedometer itself needs calibration. Or you could fit different diameter rear tires.

EXAMPLE: If you are reading say 60 when you are really going 50 then the speedo cable needs to slow down by about 20% to read more accurately. If the speedo drive has a 17 tooth cog in it try to find a cog that reduces by 20%. 17 X .20 = 3.4 teeth... 17 + 3.4 = 20.4 teeth, the closest is a 20 tooth cog.

Teeth	% change	50 mph reading
16	106.25%	53.1
17	100.00%	50.0
18	94.44%	47.2
19	89.47%	44.7

Correction Table, increase Teeth by:

Actual mph	Desired mph	Tooth
40	50	3+
43	50	2+
47	50	1+
50	50	0+

Part Numbers

NOTE: while they are color-coded, order by part number, not by color. For example, 63-series and 56-series cogs (pinion gears) use different color coding.
They are easy to replace by removing the roll pin...use your original Cog Body (Sleeve).