Speedometer question
06-06-2005 | 05:57 PM
#1
Thread Starter
Guinea Pig
Joined: Apr 2005
Posts: 4,104
Likes: 2
From: At home
Speedometer question
Does anyone know how the speedometer senses how fast the car is going? Does it pick it up from all 4 wheels? Or does it just sense 1 wheel? I know we have VSA that senses all 4 wheels, is the speedo linked up to that somehow?
06-06-2005 | 06:31 PM
#2
Instructor
Joined: Jun 2004
Posts: 236
Likes: 0
Front wheels...we have alot of asphalt (the stuff that gets real slick when wet and looks kinda like tar) around here and whenever it gets wet I like to pretend the car has enough power to do a standing burn out with out the brake...I've got the car up to about 80 while actually moving about 15mph
06-07-2005 | 10:58 AM
#5
Three Wheelin'
Joined: Jul 2003
Posts: 1,737
Likes: 0
Yes... both front wheels. To prove this... just get one side spinning and you will see the speedo go up... then get other side to spin (on ice) and you will see speedo go up. Unless they are sensing drive shart speed... in which case they only need one sensor.
06-07-2005 | 01:10 PM
#7
Rep'n Taxbrain.com
Joined: Aug 2004
Posts: 7,075
Likes: 3
From: N. Cali-forn-i-a
Originally Posted by JTso
I believe the speed is monitored by the VSS (vehicle speed sensor). I have to look at the manual to see where it is.
I have my Pioneer N1 hooked up to the VSS, and that helps the N1 gauage some of my performance. The VSS will send out a certain number of pulses per sec based on how fast you're going.
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06-07-2005 | 04:23 PM
#9
Rep'n Taxbrain.com
Joined: Aug 2004
Posts: 7,075
Likes: 3
From: N. Cali-forn-i-a
Originally Posted by CJams
Ah ha! Saweeet! Did you hook that up yourself? Pioneer N1...is that seperate from your navi screen? Where is the VSS located.
I hooked up the VSS myself. It's located on one of the harnesses that goes into the ECU.
06-10-2005 | 05:16 PM
#10
AutoX'er
Joined: Oct 2004
Posts: 45
Likes: 0
From: Toronto
The VSP sensor is in the front of your tranny, roughly inline with the ring gear on your diff. It is a non contact type 'hall effect' sensor.
The sensor will have three wires, the black one is ground, the others should be yellow and green. I belive yellow is power and green is signal. Your car won't start if you mix the green and yellow wire up.
-SWRT
The sensor will have three wires, the black one is ground, the others should be yellow and green. I belive yellow is power and green is signal. Your car won't start if you mix the green and yellow wire up.
-SWRT
06-29-2005 | 11:05 PM
#11
Intermediate
Joined: Jun 2005
Posts: 28
Likes: 0
From: Baton Rouge, LA
Hi, I'm new here so forgive me if I get "talky"... 
Not too much help since SWRT really answered the original question - but a story to tell.
But...
Speedometers have always been connected so that it reads the speed from or near the transmission. Not from the wheels themselves, but from whatever is powering the drive wheels. That's why you will get a higher than true speed reading when spinning out. The drivetrain that the sensor is attached to is what's spinning those wheels faster.
In the old days (before everything was electronic) there was an actual cable with square shaft fixed to each end that could freely spin inside an outer sheath. One end fit into the back of the speedometer and the other end was routed through the firewall to a fitting out the side of the back end of the transmission. This transmission fitting would spin at a fixed geared speed with the final drive speed of the driveshaft. That fitting would spin the cable, and in the speedometer end would spin a magnet. A rotating cup-like housing with a shaft that had the speedometer needle attached covered the magnet. The cup/shaft was held in tension by a spiral spring but would allow the cup to turn up to a certain amount as the magnet spun inside of it. The faster the magnet spun, the more the cup would turn, the more the needle turned giving a faster speed reading against the numbers on the faceplate. As the spin of the magnet slowed down, the spring would pull the cup and needle back to 0. Obviously, all this had to be calibrated properly - how strong the magnet was, how reactive the metal cup was, how strong the spring was, and how tight it was resting at "0" (which was adjustable).
I learned all this driving an old 1960 Chevy Apache C-10 pickup back in high school and first year in college. This was from '81 to '84. For the first year I had it, the speedometer didn't work (it never worked for the guy I bought it from, but he wasn't the original owner himself). One summer day looking to finally fix it, I found that it had no speedometer cable at all. But, I did discover where it attached near the end of the transmission by jacking the rear-end, putting it in neutral and spinning the wheels for forward motion. A little fitting was turning with a square socket in the middle. Breaking into the speedometer, I found another problem - the needle was broken from the shaft. After a trip to the old Hi-Lo parts store, I had a length of speedometer cable in hand and a tube of J-B Weld (to "glue" the needle back onto the shaft). I was soon getting an actual speed reading on my speedometer for the first time in who knows how many years. No telling how many miles the truck really had since the odometer (geared to the speedometer cable attachment) was also out of commission for all that time.
Anyway, it's all electronically read now, but the sensor itself is still on or near the output end of the transmission or differential on most vehicles.
Not too much help since SWRT really answered the original question - but a story to tell.
But...
Speedometers have always been connected so that it reads the speed from or near the transmission. Not from the wheels themselves, but from whatever is powering the drive wheels. That's why you will get a higher than true speed reading when spinning out. The drivetrain that the sensor is attached to is what's spinning those wheels faster.
In the old days (before everything was electronic) there was an actual cable with square shaft fixed to each end that could freely spin inside an outer sheath. One end fit into the back of the speedometer and the other end was routed through the firewall to a fitting out the side of the back end of the transmission. This transmission fitting would spin at a fixed geared speed with the final drive speed of the driveshaft. That fitting would spin the cable, and in the speedometer end would spin a magnet. A rotating cup-like housing with a shaft that had the speedometer needle attached covered the magnet. The cup/shaft was held in tension by a spiral spring but would allow the cup to turn up to a certain amount as the magnet spun inside of it. The faster the magnet spun, the more the cup would turn, the more the needle turned giving a faster speed reading against the numbers on the faceplate. As the spin of the magnet slowed down, the spring would pull the cup and needle back to 0. Obviously, all this had to be calibrated properly - how strong the magnet was, how reactive the metal cup was, how strong the spring was, and how tight it was resting at "0" (which was adjustable).
I learned all this driving an old 1960 Chevy Apache C-10 pickup back in high school and first year in college. This was from '81 to '84. For the first year I had it, the speedometer didn't work (it never worked for the guy I bought it from, but he wasn't the original owner himself). One summer day looking to finally fix it, I found that it had no speedometer cable at all. But, I did discover where it attached near the end of the transmission by jacking the rear-end, putting it in neutral and spinning the wheels for forward motion. A little fitting was turning with a square socket in the middle. Breaking into the speedometer, I found another problem - the needle was broken from the shaft. After a trip to the old Hi-Lo parts store, I had a length of speedometer cable in hand and a tube of J-B Weld (to "glue" the needle back onto the shaft). I was soon getting an actual speed reading on my speedometer for the first time in who knows how many years. No telling how many miles the truck really had since the odometer (geared to the speedometer cable attachment) was also out of commission for all that time.
Anyway, it's all electronically read now, but the sensor itself is still on or near the output end of the transmission or differential on most vehicles.
06-30-2005 | 12:47 AM
#12
Drifting
Joined: Sep 2003
Posts: 2,788
Likes: 5
From: Atlanta, Ga.
Originally Posted by jakesdad
Hi, I'm new here so forgive me if I get "talky"...
Not too much help since SWRT really answered the original question - but a story to tell.
But...
Speedometers have always been connected so that it reads the speed from or near the transmission. Not from the wheels themselves, but from whatever is powering the drive wheels. That's why you will get a higher than true speed reading when spinning out. The drivetrain that the sensor is attached to is what's spinning those wheels faster.
In the old days (before everything was electronic) there was an actual cable with square shaft fixed to each end that could freely spin inside an outer sheath. One end fit into the back of the speedometer and the other end was routed through the firewall to a fitting out the side of the back end of the transmission. This transmission fitting would spin at a fixed geared speed with the final drive speed of the driveshaft. That fitting would spin the cable, and in the speedometer end would spin a magnet. A rotating cup-like housing with a shaft that had the speedometer needle attached covered the magnet. The cup/shaft was held in tension by a spiral spring but would allow the cup to turn up to a certain amount as the magnet spun inside of it. The faster the magnet spun, the more the cup would turn, the more the needle turned giving a faster speed reading against the numbers on the faceplate. As the spin of the magnet slowed down, the spring would pull the cup and needle back to 0. Obviously, all this had to be calibrated properly - how strong the magnet was, how reactive the metal cup was, how strong the spring was, and how tight it was resting at "0" (which was adjustable).
I learned all this driving an old 1960 Chevy Apache C-10 pickup back in high school and first year in college. This was from '81 to '84. For the first year I had it, the speedometer didn't work (it never worked for the guy I bought it from, but he wasn't the original owner himself). One summer day looking to finally fix it, I found that it had no speedometer cable at all. But, I did discover where it attached near the end of the transmission by jacking the rear-end, putting it in neutral and spinning the wheels for forward motion. A little fitting was turning with a square socket in the middle. Breaking into the speedometer, I found another problem - the needle was broken from the shaft. After a trip to the old Hi-Lo parts store, I had a length of speedometer cable in hand and a tube of J-B Weld (to "glue" the needle back onto the shaft). I was soon getting an actual speed reading on my speedometer for the first time in who knows how many years. No telling how many miles the truck really had since the odometer (geared to the speedometer cable attachment) was also out of commission for all that time.
Anyway, it's all electronically read now, but the sensor itself is still on or near the output end of the transmission or differential on most vehicles.
Not too much help since SWRT really answered the original question - but a story to tell.
But...
Speedometers have always been connected so that it reads the speed from or near the transmission. Not from the wheels themselves, but from whatever is powering the drive wheels. That's why you will get a higher than true speed reading when spinning out. The drivetrain that the sensor is attached to is what's spinning those wheels faster.
In the old days (before everything was electronic) there was an actual cable with square shaft fixed to each end that could freely spin inside an outer sheath. One end fit into the back of the speedometer and the other end was routed through the firewall to a fitting out the side of the back end of the transmission. This transmission fitting would spin at a fixed geared speed with the final drive speed of the driveshaft. That fitting would spin the cable, and in the speedometer end would spin a magnet. A rotating cup-like housing with a shaft that had the speedometer needle attached covered the magnet. The cup/shaft was held in tension by a spiral spring but would allow the cup to turn up to a certain amount as the magnet spun inside of it. The faster the magnet spun, the more the cup would turn, the more the needle turned giving a faster speed reading against the numbers on the faceplate. As the spin of the magnet slowed down, the spring would pull the cup and needle back to 0. Obviously, all this had to be calibrated properly - how strong the magnet was, how reactive the metal cup was, how strong the spring was, and how tight it was resting at "0" (which was adjustable).
I learned all this driving an old 1960 Chevy Apache C-10 pickup back in high school and first year in college. This was from '81 to '84. For the first year I had it, the speedometer didn't work (it never worked for the guy I bought it from, but he wasn't the original owner himself). One summer day looking to finally fix it, I found that it had no speedometer cable at all. But, I did discover where it attached near the end of the transmission by jacking the rear-end, putting it in neutral and spinning the wheels for forward motion. A little fitting was turning with a square socket in the middle. Breaking into the speedometer, I found another problem - the needle was broken from the shaft. After a trip to the old Hi-Lo parts store, I had a length of speedometer cable in hand and a tube of J-B Weld (to "glue" the needle back onto the shaft). I was soon getting an actual speed reading on my speedometer for the first time in who knows how many years. No telling how many miles the truck really had since the odometer (geared to the speedometer cable attachment) was also out of commission for all that time.
Anyway, it's all electronically read now, but the sensor itself is still on or near the output end of the transmission or differential on most vehicles.
Welcome to the board.
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