How to: Speedometer Gear Color Code Specification Chart With Formulas, And Ford Part Numbers.

Changing The Speedometer Gearing.

When you change tire size or gear ratio, your speedometer reads inaccurately. To fix this you have to change the speedometer gear (change the number of teeth). First you need to find out the current speedometer gear's tooth count. You have to remove the speedometer cable from the transmission (instructions below). The gears are color coded. Here is the chart with Ford part numbers:

Manual Transmissions:

16-teeth-wine (C0DZ-A)

17-teeth-white (C3DZ-C)

18-teeth-yellow (C0DD-B)

19-teeth-pink (C0DZ-B)

20-teeth-black (C1DZ-A)

21-teeth-red (C4OZ-A)

Auto Transmissions:

16-teeth-blue (D0AZ-A)

17-teeth-green (C7SZ-A)

18-teeth-gray (C7SZ-B)

19-teeth-tan (C7VY-A)

20-teeth-orange (C8SZ-B)

21-teeth-purple (D0OZ-B)

Then Use This Formula:

New Teeth = (Current Teeth x Speedo Reading)/Actual Speed.

Ford Motorsports Also Uses This Formula:

Driven Gear Teeth = (Drive Gear Teeth x Axle Ratio x Tire Rev. Per Mile) / 1000.

FourWheeler Magazine uses:

Actual MPH= (New Tire Diameter x Indicated MPH) / Old Tire Diameter.

The first two formulas will tell you how many teeth your speedometer gear needs. You can obtain the new gear from your local Ford dealer. The swap will provide you with the approximate correct MPH readings.

The speedometer gear is attached to the black cable going into your transmission's tailhousing. 4wd vehicles - the speedo sensor is located near the rear output flange of the transfer case. 95, and above did not use a cable. Digital dash doesn't use a cable either. 98, and above started to use the sensor on the rear differential. This is also used for the ABS. There is a single bolt, and retaining ring holding it in. Once you remove the bolt, and ring, the gear, and cable will slide right out. The gear is attached to the cable with a small clip which could be removed with a small screwdriver.

Note: My 89 Aerostar has digital dash, and doesn't have a cable, but has the VSS on the extension housing. My 93 Aerostar with analog dash does not have a cable, or a VSS on the extension housing. It only has the sensor on the rear differential.

2WD vehicles:
Refer to the chart for automatic transmissions.

4WD vehicles:
Refer to the chart for manual transmissions. 4WD vehicles use the same gear as a manual transmission regardless if the transmission is a manual, or an automatic.

Very nice post.

Thanks for the compliment. I can't take full credit for it. It was compiled from information on this website, and from the Ranger Station's website. I was hoping that it might become a sticky in the Transmission section. Maybe if you rate this thread, and give a recommendation it might be.

One note..... the 4wd Explorers use the manaul teeth. Doesn't matter if it's auto or manaul tranny. 2WD uses the auto teeth.

Great post - should help out a lot of people

-Drew

Good post! Question. Does anyone know what the standard teeth count is for a 94 Explorer, stock 2wd? Also, if I'm not changing the gear yet, can I just remove the clip and pull the cable off without unbolting the attachment?

I've been meaning to change mine out (37s and 4.88s changes the speedo just a little bit over 28.5s and 3.27s )...just been too lazy to compile all the info from all the threads to figure out what I'll need. Nice post.

Jason94sport said:

One note..... the 4WD Explorers use the manual teeth. Doesn't matter if it's an auto, or manual tranny. 2WD uses the auto teeth.

Click to expand...

Thanks for the information! I'll add this to my list. Is this the case with all Ford 4WDs, or just on the Explorer 4WDs?

Here are 4 links for online speedometer gear computation programs:
http://www.bgsoflex.com/speedo1.html
http://www.jeeptech.com/javaAps/Speedo.html
http://www.sccoa.com/faq/speedgr.html
http://www.4lo.com/4LoCalc.htm

Here is a vehicle speed sensor (VSS) with the speedometer gear on the bottom. The metal bracket in the center is the piece that holds it down. The one pictured is for older vehicles without any electrical connector. Newer vehicles have a 2 pin electrical connector. That is what sends the signal to the PCM. The later model vehicles don't use this at all (98, and above). They get their signal from the sensor on the differential.

Vehicle Speed Sensor Kit.
This kit enables a 4L60E transmission (electronically controlled 700R4) to read vehicle speed in order to calculate when to shift. Use of this kit allows you to retain the mechanical speedometer in your early model car or street rod. This kit is an upgrade from the older sensors.

Here is an ABS speed sensor:

Notice the resemblance between this sensor, and the one in the picture above. Both have no gear on the end.

BrooklynBay said:

Thanks for the information! I'll add this to my list. Is this the case with all Ford 4WDs, or just on the Explorer 4WDs?

Click to expand...

I'm not sure. This was my experience when I swapped my 4WD Explorer for a 2WD Explorer.

VSS used on '87-92 trucks for cruise & E4OD applications.

Here is a description of the VSS that I found on this link: http://fordfuelinjection.com/index.php?p=33

Vehicle Speed Sensor (VSS)

The Vehicle Speed Sensor (VSS) is a small signal generator that is turned by a gear inside the transmission assembly. The Vehicle Speed Sensor produces 8 pulses per rotation, which a stock computer assumes 8,000 pulses per mile. The Vehicle Speed Sensor (VSS) is a variable reluctance sensor that generates a waveform with a frequency that is proportional to vehicle road speed. When the vehicle is moving slowly, the sensor produces a low frequency signal. As the vehicle speed increases, the sensor produces a higher frequency signal. The Vehicle Speed Sensor (VSS) supplies this signal to the components that require vehicle speed information including the speed control amplifier for cruise control equipped vehicles, and computer. The computer uses the VSS signal for emissions control programs and speed limiters. The emissions programming can cause a manual transmission vehicle to stall out while decelerating if no VSS is used.

Here is a troubleshooting artice that I found on this link: http://autorepair.about.com/library/faqs/bl224i.htm.

1992 Ford Explorer lost cruise control, and overdrive.

Q. Vince, I have a 1992 Ford Explorer with a 4.0 liter V-6, and automatic transmission. It had Cruise Control. I believe it has ABS, but may only be a partial system. It ran fine until about 105,000 miles when I left it at the Airport garage for a three day trip out of town. When I came home, I hopped in the truck, and took off up the expressway. For the first two miles all was fine.
Then the O/D slipped in, and out three or four times, and hasn't been seen since. However, a few days later I was on a long back road commuting to work at slower speeds when I went to use the cruise, and it wouldn't hold the speed. I can't even tell if the system is coming online.

I checked the fuses, and relays. Nothing is blown. I am hoping to get to Autozone to get the codes read. Any idea what systems might be linked that would cause O/D, and Cruise Control to shutdown simultaneously? Could the VSS do it?

Thanks,
Dan

A. It could be the Vehicle Speed Sensor/Cruise Control Transducer. You can test it easily enough. Of course if the problem is intermittent the test will be inconclusive.

Disconnect the speed sensor connector, then connect an ohmmeter between dark green/white, and black wires.
A reading of 180-250 ohms should be obtained. A reading of 0 ohms indicates a shorted coil, and an infinite reading indicates an open coil. Replace the sensor if a proper reading has not been obtained. The VSS is located on the output housing of the transmission or the transfer case with all wheel drive.

The Vehicle Speed Sensor (VSS) is a magnetic pulse generator driven by the transmission's speedometer gear. The VSS produces 16 AC signals per revolution, and sends this signal to the Powertrain Control Module (PCM).

The PCM converts this signal to a vehicle speed value, and stores that value in RAM memory. The PCM uses this value to aid in controlling torque converter lock-up, coolant fan control, vehicle speed control, air/fuel ratio, and ignition timing.

Here is another one: http://autorepair.about.com/library/faqs/bl481g.htm

Ford Windstar speedometer problems.

Q. Hello, Thank you for taking my question. We have a 1998 Ford Windstar with 78,000 miles. We have the 3.8 liter V-6, ABS, power everything and electronic overdrive transmission. Recently the speedometer began to go dead intermittently. When this happens the engine does not change its operation just a dead speedometer. However, it seems that the engine and transmission are not communicating with each other with the speedometer dead. The transmission shifts high up in the rev range, I can get by this by using the shift lever. Once I shift by hand the problems dies down, but the shifting is not as smooth as it is when the speedometer works.

Once the speedometer decides to come back on line the shifting smooths out and all is well. I brought the van to the dealer. They told me the transmission was shot, and asked for $3,000.00 to replace it. I said no, and brought the van to my independent mechanic. He serviced the transmission, and found no problems. However, he could not get the speedometer to go dead, and was getting no error codes, so he was unable to diagnose the problem. Any help that you could provide would be appreciated. I know my way around the engine mechanically, but the electronic controls, and engine management system I have no experience with. If my problem is a sensor, board, whatever, I can replace it but can't diagnose it.

Thanks,
Russell

A. Without seeing it, I would have to say the most likely problem is with the Vehicle Speed Sensor (VSS). The VSS signal transmits vehicle speed to the Powertrain Control Module (PCM) which uses the signal to control engine, and transmission operating conditions. It also sends a signal to the speedometer to display vehicle speed.

The Vehicle Speed Sensor is located on the transaxle, at the rear of the engine. I would check the harness connector to be sure it is clean, and connected tightly.

Check the wiring for cuts, and chaffing. Since it is fairly inexpensive, only about $42.00 from Ford, you may want to consider replacing it, at least to eliminate it as a possibility.

When the PCM no longer receives the VSS signal, it puts the transmission into a default mode to prevent transmission damage, hence the hard, high shift points.

Here is another article on speed sensors from this link: Dead Link Removed
Dead Link Removed
The PM (permanent magnet) VSS is usually located on the transmission case in the speedometer cable opening. It will either replace the cable (for electronic speedometers) or mount on the transmission in series with the cable (for mechanical speedometers).

The permanent magnet vehicle speed sensor (VSS) consists of a permanent magnet generator, which produces a pulsing (ac) voltage when it spins. Three miles per hour is approximately the speed at which the ECU recognizes its output. The voltage level, and number of pulses increase with vehicle speed.

Since ECU's cannot read ac voltage easily, a buffer module is often used to amplify, and convert it to a digital (on/off) signal which can be read easily by the ecu. The buffer module also sends the signal to the electronic cruise control, and electronic speedometer systems.

Newer GM, Ford, and Chrysler ECU's amplify, and convert the ac signal to digital internally so no buffer module is needed.

The computer uses VSS input to operate the following:

1. The idle air control valve.

2. The canister purge system.

3. The torque converter clutch.

4. Cruise control.

5. Distance traveled.

6. Deceleration.

The PM (permanent magnet) VSS circuit can be tested using a scan tester or digital volt meter while driving the vehicle. It also can be checked for proper resistance using a digital ohmmeter. A typical resistance value would be 300 to 700 Ohms*. It can also be tested for proper output by connecting a digital volt meter across the two terminals on the VSS while turning the drive shaft. A typical specified output would be 1.5 to 6.5 volts at 20 mph*.

* Specifications vary. See service manual for correct specifications.

Dead Link Removed

Another type of VSS is the optical VSS. This type is used by GM. It is located inside the speedometer head and is attached to the back of the instrument cluster. It consists of a photo cell and L.E.D. mounted in a housing, which is permanently wired to the buffer circuit (the buffer/L.E.D./photocell is an assembly). A spinning mirrored reflector with two blades completes the system.

The L.E.D. is lighted any time the ignition switch is turned on. As the speedometer cable turns, the reflector blades pass through the light beam from the L.E.D. twice each revolution. The light beam is reflected back to the photo cell. The photo cell generates an electrical signal to the buffer, which indicates the vehicle speed. The buffer then sends a digital (on/off) signal to the computer which interprets the number of pulses per mile as vehicle speed.

Caution: As simple as this system seems to be, trouble codes associated with VSS problems utilize other sensor inputs. Refer to troubleshooting guides for proper diagnosis!

Here is an internal view of the speedometer drive gear inside of a 1354 transfer case (photo courtesy of Glacier991's photo gallery):

Here's a link to a speedometer gear chart with part numbers: http://www.tciauto.com/components/speedometer_gears.htm. This link is from the same website with a speedometer gear computation program in addition to a chart: http://www.tciauto.com/tech_info/speedo_gears.htm.

does any one know where to get these gears? i replaced the t-case in my 97 v6 sohc 4x4 and the origonal gear got chewed up. i ordered a new from ford and it got chewed up to. partially my fault cause the orig was a 19 tooth pink right hand drive new was 19 tooth left hand drive.....minor difference...not really. any way ford says they are discontinued......what am i supposed to do now as the vss controls core than just cruise and odometer to? if any one may have one they dont need ill buy.

thanks, steve

This link has information about calibrating speedometers: Dead Link Removed. Check the tech section on that website for other useful links: Dead Link Removed. They have gear calculators too.