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Discussion Starter · #1 · (Edited)
Recently purchased a 1992 Silverado (WT), with the V-6. The speedometer is reading about 15 mph fast, it has the correct size tires as the sticker on the door (225-75-15) if I remember correctly. It appears the Trans is a 700-R4. I have no idea the history of the truck, if the trans was swamped at some point or what. But I see I can buy "kits" of multiple speedo drive gears or varying colors and number of teeth, I believe I will need to slow mine down with a larger drive gear. My two questions are: 1. Approximately how many teeth are responsible for how many mph? ( 3 teeth larger slows down by "X" MPH?). And 2. If I take mine out to see what I have in there, as far as color and number goes, will I loose all of the fluid in the trans? or just a bit? or none? Thanks.

edit: So I just read somewhere that the "Drive Gear", which I am talking about here, will need to have "fewer" teeth to slow down the "Driven Gear" that place where I saw that goes on to say that for each tooth added or , In my case subtracted, will have approx. a 10mph difference? Does that sound about right? still wondering about my fluid question.
 

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Need to know if your trans has the gear driven pulse generator or the large diameter sensor with 40 tooth reluctor on the output shaft? Does your trans have a TV cable hooked to the engine throttle or is it a 4L60E trans?
 
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Discussion Starter · #4 ·
Need to know if your trans has the gear driven pulse generator or the large diameter sensor with 40 tooth reluctor on the output shaft? Does your trans have a TV cable hooked to the engine throttle or is it a 4L60E trans?


Yes it has the TV cable.
 

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A ratio adapter is NOT the way to go IMHO. Too many moving parts and it does nothing to adress why it is off
Correcting the speedo wil require a little math
Loosely speaking ,One tooth will make 2-3 MPH difference.
Post the gear ratio so we can run some numbers.
Also pull the speedo drive gear assembly out and look at the color of the gears Both drive gear and driven gear
You will need to know which ones you have because after you move a few drive gear sizes the driven gear also need to be changed.
Been there and done that

There is also likely a DRAC ( digital Ratio Adapter Control) Module in the dash as well.
It generates a square wave signal that runs the speedo/odometer. It is calibrated for the truck
Prolly need to locate that and check the calibration number to be sure it is correct
I have a list somewhere , I think, That I can check if needed.
The DRAC will have 3 bold letters on it.It is a little box, nearly white in color.It may have 1 or 2 connectors on it.
 

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Contact speedhut. I know they make a box that allows you to convert a cable driven to gps driven. One of those "I should have bought this years ago" items.
But I am unsure if they ever made anything for your cluster that would "plug in" . You never know unless you ask.

 

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No speedo drive cable on these transmissions. the 700R (4L60) has a throttle pressure cable 4L60E is all electronic. Neither has a drive cable for the speedo

Where did OP go?
 

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Later design 4L60 large diameter VSS ... The tail housing would have 4 bolts holding it to main trans case. With this sensor in the tail housing.
 

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Discussion Starter · #10 ·
So I had some time this weekend and slide under the truck.. sure enough its the 4L60E. I see they make a thing called an Electronic Ratio Adapter. Not sure I really want to spend near 200.00 for one though. Is it possible that the factory speed sensor could be bad? and causing it to read fast? Just not sure what's going on?
 

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The speed reading is sensitive to final gear ratio and tire size that the computer is programmed for. Mismatches of any of these will present errors on the speedometer. There is a module on the back of the instrument panel called a DRAC that GM uses to match tranny clock speed output to the speedometer for different gearing and tire size combinations.

Your 92 should have a 700R4/4L60 (no E). The 4L60E uses a different computer where the shift programming is included in the computer stating in 1993. The 1992 at least in original form did not have a computer capable of controlling the transmission . The 4L60E is identifiable by a big black electrical box on the drivers side of the main case and a nearly wrist size wire bundle making a connector attachment into the lower main case on the passenger side.

Bogie
 

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So I had some time this weekend and slide under the truck.. sure enough its the 4L60E. I see they make a thing called an Electronic Ratio Adapter. Not sure I really want to spend near 200.00 for one though. Is it possible that the factory speed sensor could be bad? and causing it to read fast? Just not sure what's going on?
check if the rear axle is the matching ratio for the truck.
THIS ^^^^^^^^^^^^^^^

Dont buy an adapter
you need to find out EXACTLY which gear ratio you have.
If the rear end ratio is different from what the truck was born with, you will likely need to change the DRAC module.
Now that being said , you CAN re calibrate the DRAC module. Some have mini switches inside you can change.Others have a set of resistors inside you can solder/unsolder /change to get where you need to be.
 
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