My last bug to wig out... speedometer question

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mobileaudio25

G-Body Guru
Jan 12, 2012
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columbus, ohio
I will look in the morning with a flashlight and see if I can tell what color the gear is. I noticed my gear was yellow oh 22tooth and the link said it should be gray.

My mechanic said one of the reason the speedo was jumping around and not consistent was because the car was on jack stands and it needed to be on pavement under a load. Does that sound correct ?
 

ttype

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Jan 30, 2017
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Brockville, Ontario.
speedometers in the past were gauged to turn 1000 turns per mile right up to the signal generator years(tbi +) snowmobiles, motorcycles, atv's, cars/trucks... i have seen correctors installed on transmissions from time to time at pick 'n pulls. could be something to look into(bigger yards mind you, a while back too) if your car has a cruise control unit in it, could always disconnect speedo cable from the fender mounted module, place it into a cardboard holder with a circle drawn around the cable end, put a little tape flag on it, then measure out 52' 9" from the center of your rear wheel, then count how many times your tape flag turns. see how many turns it does... 9 or 11 turns is an easy enuf fix. an old timer told me about it. 10 percent would be an easy fix. if not, speedo gears. ( then to tiresize.com compatator for fine tuning)

those correctors i saw were 10 percent correctors. great for tire changes in 4x4 trucks, but more importantly going from 3.08 to 3.42, 3.42 to 3.73 or 3.73 to 4.10, 4.10 to 4.56 etc. that's if you have more time than money of course...

i could stand to be corrected though...
 
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mobileaudio25

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Jan 12, 2012
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columbus, ohio
I looked inside of my speedometer gear housing opening and saw a purple drive gear in there. I talked to a guy at the speedometer shop here in Columbus and he said the speedometer should still work correctly with the rear wheels off of the ground.

my new speedo gear housing came today in the mail. I've never messed with these but I'm assuming if the gear housing is able to be mounted correctly that the plastic gears inside the transmission will align themselves up naturally when you push the housing in?

I put everything back together and installed the cable in the gear housing. I didn't put the gauge on the cable because I'm waiting for some graphite lube for the cable. I took it for a test drive and noticed the cable wasn't spinning when I was driving.

I am able to twist the cable from inside the car by hand without any resistance. Since the car is in park I shouldn't be able to twist the cable from inside the car without feeling some type of resistance should I?
 

Longroof79

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It sounds like the gears aren't meshing properly. When you installed the drive gear on the tailshaft, you did include the clip that locks the gear onto the shaft?
Also make sure the square end of the cable fits properly in the end of the driven gear.

You can test your speedometer head by connecting the cable to the speedo, and hooking up a cordless drill onto the opposite end.
 

mobileaudio25

G-Body Guru
Jan 12, 2012
518
161
43
columbus, ohio
I looked inside of my speedometer gear housing opening and saw a purple drive gear in there. I talked to a guy at the speedometer shop here in Columbus and he said the speedometer should still work correctly with the rear wheels off of the ground.

my new speedo gear housing came today in the mail. I've never messes with these but I'm assuming if the gear housing is able to be mounted correctly that the plastic gears inside the transmission will align themselves up naturally when you push the housing in?

I put everything back together and installed the cable in the gear housing. I didn't put the gauge on the cable because I'm waiting for some graphite lube for the cable. I took it for a test drive and noticed the cable wasn't spinning when I was driving.

I am able to twist the cable from inside the car by hand without much resistance. Since the car is in park I shouldn't be able to twist the cable from inside the car without feeling some type of resistance shouldnt I?
It sounds like the gears aren't meshing properly. When you installed the drive gear on the tailshaft, you did include the clip that locks the gear onto the shaft?
Also make sure the square end of the cable fits properly in the end of the driven gear.

You can test your speedometer head by connecting the cable to the speedo, and hooking up a cordless drill onto the opposite end.

I haven't ever touched the speedo gears in the transmission. This was my first time looking into it.
Purple drive gear which from what I've seen is a 10 tooth. I have a 22 tooth driven gear and I put it into a new gear housing. I think I'm going to pull it back out and make sure everything is aligned properly. I'd rather not pull the tail housing if I don't have to.

To test the speedo which way do I run the drill? Clockwise or counterclockwise ? Can you damage the speedo my going to fast or accidentally going the wrong way or something? Thanks ! Can't wait to have this figured out.
 

pontiacgp

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Mar 31, 2006
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Kitchener, Ontario
To test the speedo which way do I run the drill? Clockwise or counterclockwise ? Can you damage the speedo my going to fast or accidentally going the wrong way or something? Thanks ! Can't wait to have this figured out.

some used car lots used to get their low mileage cars with a drill...you won't damage the speedo
 
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Longroof79

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I looked inside of my speedometer gear housing opening and saw a purple drive gear in there. I talked to a guy at the speedometer shop here in Columbus and he said the speedometer should still work correctly with the rear wheels off of the ground.

my new speedo gear housing came today in the mail. I've never messes with these but I'm assuming if the gear housing is able to be mounted correctly that the plastic gears inside the transmission will align themselves up naturally when you push the housing in?

I put everything back together and installed the cable in the gear housing. I didn't put the gauge on the cable because I'm waiting for some graphite lube for the cable. I took it for a test drive and noticed the cable wasn't spinning when I was driving.

I am able to twist the cable from inside the car by hand without much resistance. Since the car is in park I shouldn't be able to twist the cable from inside the car without feeling some type of resistance shouldnt I?


I haven't ever touched the speedo gears in the transmission. This was my first time looking into it.
Purple drive gear which from what I've seen is a 10 tooth. I have a 22 tooth driven gear and I put it into a new gear housing. I think I'm going to pull it back out and make sure everything is aligned properly. I'd rather not pull the tail housing if I don't have to.

To test the speedo which way do I run the drill? Clockwise or counterclockwise ? Can you damage the speedo my going to fast or accidentally going the wrong way or something? Thanks ! Can't wait to have this figured out.
If I recall correctly, set the drill for counter clockwise rotation. That should give you a good indication how well your speedo is working.

Have you checked the formula for calibrating your speedo gears?
By multiplying (3.73) X 20.2 and dividing that number by the tire diameter.
What is your current tire diameter?

Removing the tailshaft housing on a TH350 is not difficult. You jack up the rear of the car, that keeps the trans fluid from pouring out. remove the driveshaft and the 4-bolts that holds the housing on. You'll see the drive gear. It's attached using a small spring clip. You remove the spring clip with a pair of needle nose pliers and slide the gear off.
 

Longroof79

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I see you already did the math, so to speak. From my chart, it appears that you need 8-tooth drive gear and a 23-tooth driven gear. ..whichever comes closest to the 2.93 number.
The chart indicates a 23 tooth gear for a 2.88 ratio. and a 24-tooth gear for a 3.00 ratio.
Unfortunately. there's no in between. I'd start with the 23-tooth gear...and of course the 8-tooth drive gear. If someone has the gears cheap enough, buy the 24 tooth as well. They're relatively easy to change out.
RockAuto might be a good choice to buy speedo gears. That's the last place I bought a new driven gear.
 
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