electric speedo problems for 700r4 trans

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electric speedo problems for 700r4 trans

Postby red92s10 » Sat Apr 17, 2010 5:14 pm

i have a 92 s10 that i am trying to get the speedo correct. it has an electronic speedo and is 15mph fast. i pulled the speedo gear out and its a 40 tooth. how do i figure out how to make it accurate?
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Re: electric speedo problems for 700r4 trans

Postby 88LT1Blazer » Sat Apr 17, 2010 5:53 pm

The speedo gear is not a gear. It is a 40 tooth reluctor wheel that works with the VSS pick up sensor. There are two wires that are the low and high VSS signal. This goes to the DRAC that is mounted under the dash with the stock computer. The DRAC is a buffer to the speedo. If you changed rear gear or tire size from stock, the speedo will be off. There is an electronic ratio adapter available.
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Re: electric speedo problems for 700r4 trans

Postby Rickracer » Sat Apr 17, 2010 8:05 pm

If you can find the right DRAC for your gear ratio, that would or should correct the speedo.
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Re: electric speedo problems for 700r4 trans

Postby 88LT1Blazer » Sat Apr 17, 2010 8:17 pm

Was gonna say that. Cam be complicated :mrgreen:
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Re: electric speedo problems for 700r4 trans

Postby 88LT1Blazer » Sun Apr 18, 2010 7:30 am

This is how you modify your DRAC.
http://614streets.com/drac.html

Here is the Electronic Ratio Adapter.
http://www.transmissioncenter.net/speed ... %20adapter

Electronic Ratio Adapter (ERA)

Now You Have the Solution to Your Speedometer Problems.....

For 700R4, 4L60E and others with electronic speedometers.
ERA

#69. Any change in a vehicle's tire size or rear axle ratio will cause the speedometer reading to be inaccurate. The Electronic Ratio Adapter (ERA) is designed to correct this problem. With the ERA, you simply hook up four wires, set the DIP switches according to the calibration table included with your order, and you are ready to go.

What does the Electronic Ratio Adapter do?

The automotive industry has a great variety of part sizes, types, shapes and descriptions, but regardless of make, model or year, a few things are standard. One of those standards has been the number of revolutions a speedometer cable will make for each mile traveled. Nowadays, electronic pulses have replaced the rotating cable, but the same principle applies. The Pulse Ratio (the number of pulses per mile traveled) remains the same, regardless of speed, since the same distance is traveled and the same number of pulses have occurred each mile no matter what the speed was during that mile.

However, this Pulse Ratio can be made to vary from the true when modifications are made which change the number of electronic pulses per mile on a particular vehicle. This is most commonly caused by changing the tire size (increasing the outside diameter of the tires will cause the tire to travel further before making a complete revolution), but other modifications could have the same result. When the Pulse Ratio is thrown off, the speedometer/odometer will be inaccurate and corrections must be made.

This relative difference between true speed and the speed indicated on the speedometer is called the Variance Ratio, and it is corrected using the Electronic Ratio Adapter. Cost $169.00

Wiring Diagram of Electronic Ratio Adapter:

Electronic Ratio Adapter
(Red Wire) + 12 volts, ignition on
(Black Wire) Ground
(White Wire) Signal in from the speed sensor
(Blue Wire) Signal out to the ECM / Speedometer


Currently the Electronic Ratio Adapter is not recommended for 2000 and newer Fords and 2001 on Dodge Rams.
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Re: electric speedo problems for 700r4 trans

Postby va4cqd » Tue Apr 20, 2010 5:02 am

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Re: electric speedo problems for 700r4 trans

Postby superbee » Tue Apr 20, 2010 11:53 am

just want to say i soldered in a dip switch into my drac years ago and it worked like a charm after i found the right combination.
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Re: electric speedo problems for 700r4 trans

Postby sln007 » Fri Mar 04, 2011 4:38 pm

Do all S-10's have the DRAC? Mine is a 2002.

If so, and I can find it and get to it, I'll open it up and reset the pins.

Otherwise, it's off to get an ERA.
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