Speedo correction gear calculation please...
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 3,014
Likes: 18
From: Raleigh, NC
Speedo correction gear calculation please...
Hey CFI EFI, or anyone else with the know how to calculate the speedo correction gears, if you get a spare minute would you mind calculating the drive and driven gears I need? My car is a 91, 6 speed, and I am having a 4.09 gear set installed in the rear. It's my understanding that I'll need to do both the drive and driven gears. If someone could let me know what I need, that would be awesome!
I see that Haibeck offers the correct gears for about $125. I think I can do them cheaper if I know the tooth count to ask for at the dealership. Thanks guys!
I see that Haibeck offers the correct gears for about $125. I think I can do them cheaper if I know the tooth count to ask for at the dealership. Thanks guys!
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Here is a link to a great web site CFI-EFI sent me, I'll let you do the calculations yourself but think you will need your current rear axle ratio and tire height to get it right.
http://www.transmissioncenter.net/sp...n_______va.htm
http://www.transmissioncenter.net/sp...n_______va.htm
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
The drive gear will have to be the grey 15 tooth, 8642820. Depending on your present ratio, that is probably what you have. According to the link, a light blue, 45 tooth driven gear, part number, 25513052, will be slightly off. Double check your tire measurements. Others on the forum have reported that the 45 tooth driven gear was just right for 3.73 gears. If your present driven gear is 40 or more teeth, your VSS will work as it is. If your driven gear is 39 teeth or less, rotate the VSS 180° to allow it to work. That is as close as I can get with my books.
RACE ON!!!
RACE ON!!!
Burning Brakes
Joined: Nov 2004
Posts: 781
Likes: 0
The last I knew, Haibeck's custom made drive gears were the only nylon gears available, for accurate (within 1% or less) use with 4.09 or 4.10 rearend gears. I have heard that someone makes them cheaper, out of steel, but they need to be heated up to install and may prematurely wear the other nylon/plastic driven gear.
I believe the cheapest, readily available 'off the shelf' GM gears will only get you as close as a 3.73/3.75 rearend scenario.
I would just "bite the bullet" and get the correct set from Haibeck.
I believe the cheapest, readily available 'off the shelf' GM gears will only get you as close as a 3.73/3.75 rearend scenario.
I would just "bite the bullet" and get the correct set from Haibeck.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
speeeeeedoh
um, doesn't your car have a Vehicle Speed Sensor?
ABS sensors on the wheels?
I thought all speedos worked off the computer since 84.
The ABS sensors i was told are a way the computer checks the VSS
You might have to just do a calibration by changing the chip
wasn't 91 the last year of the TPI?
ok I have a 86 corvette, and no speedo cables
I have a 92 buick Regal, and the speedo went nuts on the way home from work one day, and in checking stuff out, I found one of the computer connector clips not plugged all the way in, and i snapped it home, and all fixed.
I have a 4+3 trans in my 57 chevy pickup, and no speedo cables
so check it out!!!
ABS sensors on the wheels?
I thought all speedos worked off the computer since 84.
The ABS sensors i was told are a way the computer checks the VSS
You might have to just do a calibration by changing the chip
wasn't 91 the last year of the TPI?
ok I have a 86 corvette, and no speedo cables
I have a 92 buick Regal, and the speedo went nuts on the way home from work one day, and in checking stuff out, I found one of the computer connector clips not plugged all the way in, and i snapped it home, and all fixed.
I have a 4+3 trans in my 57 chevy pickup, and no speedo cables
so check it out!!!
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by coupeguy2001
um, doesn't your car have a Vehicle Speed Sensor?
ABS sensors on the wheels?
I thought all speedos worked off the computer since 84.
The ABS sensors i was told are a way the computer checks the VSS
You might have to just do a calibration by changing the chip
wasn't 91 the last year of the TPI?
ok I have a 86 corvette, and no speedo cables
I have a 92 buick Regal, and the speedo went nuts on the way home from work one day, and in checking stuff out, I found one of the computer connector clips not plugged all the way in, and i snapped it home, and all fixed.
I have a 4+3 trans in my 57 chevy pickup, and no speedo cables
so check it out!!!
ABS sensors on the wheels?
I thought all speedos worked off the computer since 84.
The ABS sensors i was told are a way the computer checks the VSS
You might have to just do a calibration by changing the chip
wasn't 91 the last year of the TPI?
ok I have a 86 corvette, and no speedo cables
I have a 92 buick Regal, and the speedo went nuts on the way home from work one day, and in checking stuff out, I found one of the computer connector clips not plugged all the way in, and i snapped it home, and all fixed.
I have a 4+3 trans in my 57 chevy pickup, and no speedo cables
so check it out!!!
RACE ON!!!
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 3,014
Likes: 18
From: Raleigh, NC
I'd rather not buy from Haibeck for personal reasons, after talking with Bill B at ZFdoc.com, I have decided to go with an electronic box that wires inline with the speed signal wires. It will allow me to correct for any gear ratio that I want, and will save me having to buy another set of speedo gears later on if I should change the ratio again.
Thanks for the information CFI-EFI.
If you're ever out this way (Ft. Bragg/Fayetteville area of NC, Hell even Raleigh/Durham) let me know, first round is on me.
Thanks for the information CFI-EFI.
If you're ever out this way (Ft. Bragg/Fayetteville area of NC, Hell even Raleigh/Durham) let me know, first round is on me.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by neat
Thanks for the information CFI-EFI.
If you're ever out this way (Ft. Bragg/Fayetteville area of NC, Hell even Raleigh/Durham) let me know, first round is on me.
If you're ever out this way (Ft. Bragg/Fayetteville area of NC, Hell even Raleigh/Durham) let me know, first round is on me.
RACE ON!!!
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