Speedo calibration
#1
Junior Member
Thread Starter
Join Date: Apr 2024
Location: Pittsboro, NC
Posts: 28
Likes: 0
Received 1 Like
on
1 Post
Car: 1984 Z28
Engine: 305
Transmission: T5
Speedo calibration
Before I removed my gauge cluster, my speedometer was off by 5mph at 55 (55=60). Yes, it was a percentage, but where I live all the roads are 55mph, so its what I use as an example. But after I removed and re-installed the cluster, it is off by almost 15mph (now 47=60). I really don't want to have to pull the cluster out again, but have gotten a little better at it lately (been in and out 6 times now). I just find it tedious to get the speed cable disconnected from the back of the cluster.
Any thoughts as to how to attack, or is the cluster needing to come back out again? What would I look for or do?
Thanks!
Any thoughts as to how to attack, or is the cluster needing to come back out again? What would I look for or do?
Thanks!
#2
Senior Member
![](https://www.thirdgen.org/forums/images/ranks/tgo10.gif)
Re: Speedo calibration
Unless you swapped out speedometers I can't imagine how you would have affected the accuracy. The calibration is changed by swapping out gears at the transmission. There is a sticky thread on this and it's useful, but doesn't account for variable degradation of the speedometer magnet. I would buy a pack of various speedo gears and start experimenting. You will probably find each gear change causes about a 2mph change in the speedometer reading.
#3
Re: Speedo calibration
My guess is a binding cable or the wrong speedo gears. It's kinda' uncommon for the speedo head (cluster) to be the cause of an inaccurate speedo. Sure - it happens, but more often than not the issue is the wrong (or worn) speedo gears, or a cable that's "binding" inside the sheath causing the reading at the cluster to be a little slower than it should be.
I'd start your investigation at the VSS on the tranny. You can remove it from the tranny using a 10mm and pair of pliers in about 2 minutes. Once it's out,... Spin the square end of speedo cable and feel if there is any resistance, or does it spins freely ?? Next; (while the VSS is removed from the tranny ) temp install the VSS onto the cable and spin the plastic gear on the end of the sensor,.... does it still spin freely ?? Then; make note of the color and tooth count of the plastic speedo DRIVEN gear ( on sensor) as well as the color and tooth count of the DRIVE gear (in the tranny). FULLY inspect BOTH of those plastic gears for damage / worn teeth. Now; reinstall everything - at least for now !
At this point you'll know what speedo gears are installed, if they appear OK or damaged / worn, and if the cable spins free & smooth (into the cluster, and thru the VSS to the cluster ) properly.
Final step is to buy some gear oil (and a diff gasket if you are so inclined) and drain the rear end so you can verify your rear end gearing. ( probably time for new rear diff fluid anyway ! ) then check to verify the correct speedo gears are installed.
![driving](https://www.thirdgen.org/forums/images/smilies/driving.gif)
I'd start your investigation at the VSS on the tranny. You can remove it from the tranny using a 10mm and pair of pliers in about 2 minutes. Once it's out,... Spin the square end of speedo cable and feel if there is any resistance, or does it spins freely ?? Next; (while the VSS is removed from the tranny ) temp install the VSS onto the cable and spin the plastic gear on the end of the sensor,.... does it still spin freely ?? Then; make note of the color and tooth count of the plastic speedo DRIVEN gear ( on sensor) as well as the color and tooth count of the DRIVE gear (in the tranny). FULLY inspect BOTH of those plastic gears for damage / worn teeth. Now; reinstall everything - at least for now !
At this point you'll know what speedo gears are installed, if they appear OK or damaged / worn, and if the cable spins free & smooth (into the cluster, and thru the VSS to the cluster ) properly.
Final step is to buy some gear oil (and a diff gasket if you are so inclined) and drain the rear end so you can verify your rear end gearing. ( probably time for new rear diff fluid anyway ! ) then check to verify the correct speedo gears are installed.
![driving](https://www.thirdgen.org/forums/images/smilies/driving.gif)
The following users liked this post:
Edwardgp (08-19-2024)
#4
Supreme Member
iTrader: (3)
Join Date: Sep 2016
Location: Sunny Florida
Posts: 1,822
Received 228 Likes
on
152 Posts
Car: 96 WS6 Formula Ram Air SLP
Engine: LT1
Transmission: 6 spd
Axle/Gears: 3.42
Re: Speedo calibration
My guess is a binding cable or the wrong speedo gears. It's kinda' uncommon for the speedo head (cluster) to be the cause of an inaccurate speedo. Sure - it happens, but more often than not the issue is the wrong (or worn) speedo gears, or a cable that's "binding" inside the sheath causing the reading at the cluster to be a little slower than it should be.
I'd start your investigation at the VSS on the tranny. You can remove it from the tranny using a 10mm and pair of pliers in about 2 minutes. Once it's out,... Spin the square end of speedo cable and feel if there is any resistance, or does it spins freely ?? Next; (while the VSS is removed from the tranny ) temp install the VSS onto the cable and spin the plastic gear on the end of the sensor,.... does it still spin freely ?? Then; make note of the color and tooth count of the plastic speedo DRIVEN gear ( on sensor) as well as the color and tooth count of the DRIVE gear (in the tranny). FULLY inspect BOTH of those plastic gears for damage / worn teeth. Now; reinstall everything - at least for now !
At this point you'll know what speedo gears are installed, if they appear OK or damaged / worn, and if the cable spins free & smooth (into the cluster, and thru the VSS to the cluster ) properly.
Final step is to buy some gear oil (and a diff gasket if you are so inclined) and drain the rear end so you can verify your rear end gearing. ( probably time for new rear diff fluid anyway ! ) then check to verify the correct speedo gears are installed.
![driving](https://www.thirdgen.org/forums/images/smilies/driving.gif)
I'd start your investigation at the VSS on the tranny. You can remove it from the tranny using a 10mm and pair of pliers in about 2 minutes. Once it's out,... Spin the square end of speedo cable and feel if there is any resistance, or does it spins freely ?? Next; (while the VSS is removed from the tranny ) temp install the VSS onto the cable and spin the plastic gear on the end of the sensor,.... does it still spin freely ?? Then; make note of the color and tooth count of the plastic speedo DRIVEN gear ( on sensor) as well as the color and tooth count of the DRIVE gear (in the tranny). FULLY inspect BOTH of those plastic gears for damage / worn teeth. Now; reinstall everything - at least for now !
At this point you'll know what speedo gears are installed, if they appear OK or damaged / worn, and if the cable spins free & smooth (into the cluster, and thru the VSS to the cluster ) properly.
Final step is to buy some gear oil (and a diff gasket if you are so inclined) and drain the rear end so you can verify your rear end gearing. ( probably time for new rear diff fluid anyway ! ) then check to verify the correct speedo gears are installed.
![driving](https://www.thirdgen.org/forums/images/smilies/driving.gif)
The following users liked this post:
BizJetTech (08-19-2024)
#6
Supreme Member
iTrader: (3)
Join Date: Sep 2016
Location: Sunny Florida
Posts: 1,822
Received 228 Likes
on
152 Posts
Car: 96 WS6 Formula Ram Air SLP
Engine: LT1
Transmission: 6 spd
Axle/Gears: 3.42
Re: Speedo calibration
[QUOTE=John in RI;6541034]THANX ! ![thumbs up](https://www.thirdgen.org/forums/images/smilies/thumbsup.gif)
I've got a few gear charts,... so do a couple other members. If I don't have the right one,... I'm pretty sure this group can find what-ever I don't have.
[/QUOTE
NICE !! Exactly what I was looking for - THANKS
![thumbs up](https://www.thirdgen.org/forums/images/smilies/thumbsup.gif)
I've got a few gear charts,... so do a couple other members. If I don't have the right one,... I'm pretty sure this group can find what-ever I don't have.
![driving](https://www.thirdgen.org/forums/images/smilies/driving.gif)
NICE !! Exactly what I was looking for - THANKS
#7
Junior Member
Thread Starter
Join Date: Apr 2024
Location: Pittsboro, NC
Posts: 28
Likes: 0
Received 1 Like
on
1 Post
Car: 1984 Z28
Engine: 305
Transmission: T5
Re: Speedo calibration
I have an 84 Camaro , 305 HO,T5 transmission. Isn't the VSS on the back of the gauge cluster?
My two thoughts are
1) when I was taking the cluster in and out, I somehow damaged the yellow box on the back or the paper circuitry
2) when I pushed the speedo cable out of the way to keep it from snapping back into the cluster as I test fit it multiple times caused the cable to bind.
Are either of these valid? I have not touched the tranny or rear diff. The rear tires are oversized and so I assumed that is why the speedo was off a little. But for it to get worse was surprising.
My two thoughts are
1) when I was taking the cluster in and out, I somehow damaged the yellow box on the back or the paper circuitry
2) when I pushed the speedo cable out of the way to keep it from snapping back into the cluster as I test fit it multiple times caused the cable to bind.
Are either of these valid? I have not touched the tranny or rear diff. The rear tires are oversized and so I assumed that is why the speedo was off a little. But for it to get worse was surprising.
Trending Topics
#8
Senior Member
![](https://www.thirdgen.org/forums/images/ranks/tgo10.gif)
Re: Speedo calibration
My guess is a binding cable or the wrong speedo gears. It's kinda' uncommon for the speedo head (cluster) to be the cause of an inaccurate speedo. Sure - it happens, but more often than not the issue is the wrong (or worn) speedo gears, or a cable that's "binding" inside the sheath causing the reading at the cluster to be a little slower than it should be.
Final step is to buy some gear oil (and a diff gasket if you are so inclined) and drain the rear end so you can verify your rear end gearing. ( probably time for new rear diff fluid anyway ! ) then check to verify the correct speedo gears are installed.
Final step is to buy some gear oil (and a diff gasket if you are so inclined) and drain the rear end so you can verify your rear end gearing. ( probably time for new rear diff fluid anyway ! ) then check to verify the correct speedo gears are installed.
OP, the only OTHER reason I can think of for a sudden change (other than speedometer swap) is the cable not fully inserted and literally slipping somewhere. If so, it probably won't be long before something is worn out and complete and total failure occurs.
#9
Junior Member
Thread Starter
Join Date: Apr 2024
Location: Pittsboro, NC
Posts: 28
Likes: 0
Received 1 Like
on
1 Post
Car: 1984 Z28
Engine: 305
Transmission: T5
Re: Speedo calibration
I wonder if I didn't get the cable "all the way" in. I tucked it out of the way when I was pulling the cluster, so that when I test-fitted it the cable would not automatically connect. Once I was ready to connect it, that was a pain to get lined up again.
That could mean trying to take it all out again, pulling on the cluster or may just push more on the cable from under the hood?
That could mean trying to take it all out again, pulling on the cluster or may just push more on the cable from under the hood?
Thread
Thread Starter
Forum
Replies
Last Post