speedometer calibration
Thread Starter
Intermediate
Joined: Oct 2008
Posts: 45
Likes: 0
I have a problem of the display numeral does not match the speed of travel. Such as when I am traveling 55 mph the speedometer displays 35 mph.
I have changed the speed sensor, speed sensor gear and had the dash rebuilt for LED fadeout.
My question is: Is there a way to calibrate the speedometer or replace something in the dash assembly itself to correct this problem?
I have changed the speed sensor, speed sensor gear and had the dash rebuilt for LED fadeout.
My question is: Is there a way to calibrate the speedometer or replace something in the dash assembly itself to correct this problem?
Le Mans Master
Joined: May 1999
Posts: 6,520
Likes: 1,306
From: Windermere FL
Did you change out the rear gears recently, or did something just break?
If you change out the gears on the rear, you have to do something to correct your speedo. I am not sure what the setup is on an 84. The more modern ones have a plastic gear in the tail of the tranny that has to be swapped out to correct the VSS. It is a real PITA because you have to drop the c-beam to get to it.
Some of the older cars have a magnetic pickup so there is no gears to change. You can buy a little black box electronic converter that will change the signal for you. This is what I used. There are dip switches in the black box that you set based on the ratio of what your speedo reads and actual speed. Use a GPS to get your actual speed - it is easiest. If I remember right the little black box cost about $100+.
But if you did not change the rear end, they you have a different problem.
If you change out the gears on the rear, you have to do something to correct your speedo. I am not sure what the setup is on an 84. The more modern ones have a plastic gear in the tail of the tranny that has to be swapped out to correct the VSS. It is a real PITA because you have to drop the c-beam to get to it.
Some of the older cars have a magnetic pickup so there is no gears to change. You can buy a little black box electronic converter that will change the signal for you. This is what I used. There are dip switches in the black box that you set based on the ratio of what your speedo reads and actual speed. Use a GPS to get your actual speed - it is easiest. If I remember right the little black box cost about $100+.
But if you did not change the rear end, they you have a different problem.
Team Owner
Joined: Sep 2003
Posts: 25,414
Likes: 2,745
I'd start with just very basic confirmations. Using a GPS and traveling at GPS speeds of 30 MPH, 40 MPH, 50 MPH & 60 MPH make notes of the speedometer reading at the dash. If the error is a "consistent" percentage then the drive/driven and possibly sensor are incorrect.
Using the GPS you could also check the odometer for accuracy. Do some measured miles using the GPS vs. the odometer in the dash.
A consistent percentage error I would think easily corrected. Basic math and tinkering with drive/driven gears, maybe sensor.
If the error is NOT consistent then there's likely a cluster calibration required. I know very little (actually near nothing) regarding this calibration.
I wouldn't be concerned with anything other than the basic confirmations I mention FIRST! You're not concerned at this point with axle ratio etc.
A point of interest though might be for you to mention exactly what you changed for drive/sensor! Used from a different car, if new part #'s maybe.
BASICS FIRST !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Using the GPS you could also check the odometer for accuracy. Do some measured miles using the GPS vs. the odometer in the dash.
A consistent percentage error I would think easily corrected. Basic math and tinkering with drive/driven gears, maybe sensor.
If the error is NOT consistent then there's likely a cluster calibration required. I know very little (actually near nothing) regarding this calibration.
I wouldn't be concerned with anything other than the basic confirmations I mention FIRST! You're not concerned at this point with axle ratio etc.
A point of interest though might be for you to mention exactly what you changed for drive/sensor! Used from a different car, if new part #'s maybe.
BASICS FIRST !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Team Owner
Joined: Jul 2004
Posts: 28,502
Likes: 3,302
From: Hartford WI
In my 91, sometimes you can get away with changing the driven gear. Sometimes you have to change both the drive and driven gear. Check via GPS as to whether you have a real problem or not. If that is inaccurate, get a scantool and verify that is what the ECM is seeing. If the ECM disagrees with the speedo but agrees with GPS, you have a speedo issue.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Did the cluster ever work properly since you've owned the car?
Does the odometer work?
Might want to take the cluster semi apart to remove/unplug the odo then reconnect the cluster to the car and see what's what....odo signal is feed from the VSS also.
Thread Starter
Intermediate
Joined: Oct 2008
Posts: 45
Likes: 0
The 84 has the original rearend with 3.07 gears. I replaced the driven gear with the green 42 teeth, looks just like the one that came out of it. Then I replaced the vehicle speed sensor and nothing changed. All parts are new.
I don't know if the speedometer worked before I had the dash rebuilt because the LEDs were fadded out. The odometer did work before and after the rebuild.
I don't know what to do. I thought I could just replace something in the dash and make it work.
I don't know if the speedometer worked before I had the dash rebuilt because the LEDs were fadded out. The odometer did work before and after the rebuild.
I don't know what to do. I thought I could just replace something in the dash and make it work.
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Team Owner
Joined: Sep 2003
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You've mentioned everything EXCEPT the VSS is as original and it seems that your 42 tooth is correct for the '84 & 3.07. Assuming the drive is correct and you haven't mentioned that it isn't then the real test is a scanning device (Tech1 or equivalent).
As Akim mentioned:
Do the GPS confirmations including the odometer. Locate a Tech1, check and compare the results. I wouldn't rule out maybe a bad or packaged incorrectly VSS.
There's 2-pulse and 4-pulse VSS and they both would FIT the trans. What would an incorrect pulsed VSS do? I don't know!!
If the VSS is a recent purchase I might ask an exchange!
You don't mention where you're located either! There could be a Tech1 right around the corner from you!!!!
Are you maybe in the Northern Virginia area?
You didn't mention either if the odometer is correct! If the odometer is correct (measured miles) it would seem there's a problem with the "display"!!
The GPS is the "first tool required"!!
As Akim mentioned:
Do the GPS confirmations including the odometer. Locate a Tech1, check and compare the results. I wouldn't rule out maybe a bad or packaged incorrectly VSS.
There's 2-pulse and 4-pulse VSS and they both would FIT the trans. What would an incorrect pulsed VSS do? I don't know!!
If the VSS is a recent purchase I might ask an exchange!
You don't mention where you're located either! There could be a Tech1 right around the corner from you!!!!
Are you maybe in the Northern Virginia area?
You didn't mention either if the odometer is correct! If the odometer is correct (measured miles) it would seem there's a problem with the "display"!!
The GPS is the "first tool required"!!
Last edited by WVZR-1; Mar 25, 2010 at 09:31 PM.
Team Owner
Joined: Sep 2003
Posts: 25,414
Likes: 2,745
I don't see where you've mentioned yet where you're located!! The Tech1 might be a very useful tool.
I believe the $850 outlay without diagnostics would be "foolish"!!
