Speed Sensor Gear
Thread Starter
Heel & Toe
Joined: Apr 2007
Posts: 20
Likes: 1
Speed Sensor Gear
I have replaced my 4+3 transmission with a 6 speed, resulting in the speedometer understating my speed by about 15%.
The plastic gear on my speed sensor has 43 teeth. I believe it should be replaced by one that has 15% fewer teeth (about 37).
Is my thought process valid and if so, where do I find this part?
Thanks.
The plastic gear on my speed sensor has 43 teeth. I believe it should be replaced by one that has 15% fewer teeth (about 37).
Is my thought process valid and if so, where do I find this part?
Thanks.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
I have replaced my 4+3 transmission with a 6 speed, resulting in the speedometer understating my speed by about 15%.
The plastic gear on my speed sensor has 43 teeth. I believe it should be replaced by one that has 15% fewer teeth (about 37).
Is my thought process valid and if so, where do I find this part?
Thanks.
The plastic gear on my speed sensor has 43 teeth. I believe it should be replaced by one that has 15% fewer teeth (about 37).
Is my thought process valid and if so, where do I find this part?
Thanks.
Team Owner
Joined: Sep 2003
Posts: 25,406
Likes: 2,744
I have replaced my 4+3 transmission with a 6 speed, resulting in the speedometer understating my speed by about 15%.
The plastic gear on my speed sensor has 43 teeth. I believe it should be replaced by one that has 15% fewer teeth (about 37).
Is my thought process valid and if so, where do I find this part?
Thanks.
The plastic gear on my speed sensor has 43 teeth. I believe it should be replaced by one that has 15% fewer teeth (about 37).
Is my thought process valid and if so, where do I find this part?
Thanks.
It's much easaier to start from "scratch" with a single "known" number and that is the "drive" gear (internal to the trans). Depending on tire size and axle ratio you can determine if it will be a simple caalibration from a "driven" with the correct sensor.
You don't mention which 6-speed? To help you there needs to be "no assumptions"! Which is it? Specific model if other than a ZF S6-40. The "drive" on the ZF is a known and the math can be completed with just a tire size and axle ratio. If it's other than a ZF the "drive" number needs to be a known!!
What is the trans, the axle ratio and the tire?
Safety Car
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From: FL
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Team Owner
Joined: Sep 2003
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Your original comment:
understating my speed by about 15%.
Last edited by WVZR-1; Mar 13, 2009 at 12:49 PM.
Team Owner
Joined: Sep 2003
Posts: 25,406
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Here's a "simple" suggestion!
Assuming that the pair of gears and the sensor are a "matched set" you can go "no lower" than 40 tooth without causing a problem with the "mesh" of the drive/driven UNLESS you replace the "speed sensor"!
Buy a 40 tooth and check the calibration using a GPS or measured miles! If your math or your "GUESS" is in error you'll still have an error and be back!
Assuming that the pair of gears and the sensor are a "matched set" you can go "no lower" than 40 tooth without causing a problem with the "mesh" of the drive/driven UNLESS you replace the "speed sensor"!
Buy a 40 tooth and check the calibration using a GPS or measured miles! If your math or your "GUESS" is in error you'll still have an error and be back!
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Team Owner
Joined: Sep 2003
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A 40 tooth gear will amount to something near 15%. In MPH something near this: 60 MPH X 085 = 51 MPH. Since you can buy this for maybe $10 or less it's an "inexpensive way to see where you actually are"!!! Here's the deal "ole country boys (me included) "used to" say better than 2.5 MPH per tooth but less than or near 3.
There you are! It's SIMPLE! Spend $10 and "prove me wrong"!! You "GUESSED" at "THE ABOUT" so you might as well keep "GUESSING" at the "FIX"!
Last edited by WVZR-1; Mar 13, 2009 at 02:54 PM.
Thread Starter
Heel & Toe
Joined: Apr 2007
Posts: 20
Likes: 1
Thanks everyone. I should have been more careful with my speech, the error was 14.63% based upon 10 measured miles versus odometer reading. I corrected the problem by purchasing an Electronic Ratio Adjuster (ERA) by Abbott out of Pine Bluff Arkansas. It was a quick and complete fix. This is a black box with 12 small switches that amount to a binary coding of (I suspect) the resistence within the box. The various switches are set either off and on according to your error, in my case I used 15%. The box has 4 wires; 2 go to the spped sensor the others are power and ground.
Thanks again,
TU
Thanks again,
TU
Team Owner
Joined: Sep 2003
Posts: 25,406
Likes: 2,744
Quality solution!
Abbott is a quality product and they've been around for quite some time. If you had a first time successful install with an Abbott you'll likely have "trouble free" service. Where did you locate "the box" on the car?
I would certainly have liked you to have done the 40 tooth install though!
Are you "game" for some "simple math"?
Post your rear axle ratio/tire size/trans type/rolling radius and what you expect the drive tooth # in the transmission to be and let's try the math! You would have to measure the "rolling radius" (center of axle to ground). We could use "advertised" diameter but that usually results in an error of varying results!
I would certainly have liked you to have done the 40 tooth install though!
Are you "game" for some "simple math"?
Post your rear axle ratio/tire size/trans type/rolling radius and what you expect the drive tooth # in the transmission to be and let's try the math! You would have to measure the "rolling radius" (center of axle to ground). We could use "advertised" diameter but that usually results in an error of varying results!
