Help with 3.73 gears and speedometer
Thread Starter
Le Mans Master
Joined: Jul 1999
Posts: 5,005
Likes: 38
From: jackson nj
Help with 3.73 gears and speedometer
I'm thinking of installing 3.73 gears into my Dana 44 before installing it into my C4. The car is used for drag racing and very minimal street duty but my question is about the speedometer. I cannot seem to find a speedo gear that will work with the 3.73 gears, has anybody installed this gear ratio and changed to the "correct" speedometer gear? If so, where did you get it from?
Melting Slicks
Joined: May 2004
Posts: 2,856
Likes: 187
From: Earth
I forget the name of the company I got my 45 tooth gear from. I'll look when I get home. I paid $15 shipped for it. I do remember I googled it when i found the company but can't remember what i googled.
Thread Starter
Le Mans Master
Joined: Jul 1999
Posts: 5,005
Likes: 38
From: jackson nj
Racer
Joined: Feb 2006
Posts: 460
Likes: 0
From: MN
I went here
http://webpages.charter.net/khasting...peedocalc.html
Then ordered the parts from the local chevy dealer.
I changed wheel and tire size, so plan ahead.
http://webpages.charter.net/khasting...peedocalc.html
Then ordered the parts from the local chevy dealer.
I changed wheel and tire size, so plan ahead.
Pro
Joined: Apr 2007
Posts: 567
Likes: 36
From: Fairfax VA
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Team Owner
Joined: Sep 2003
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Everyone refers to the 45 tooth driven but it's an effective correction ONLY when used with the correct drive gear and the correct VSS to maintain the correct "pitch" to the drive gear. The only factory '89 A4 drive gear is a 17 tooth and that will not allow a correction with the addition of only a 45 tooth gear and a correct VSS. You will need to change the drive to a 15 tooth. The 15 tooth is available for the A4. It's not a problem. If your '89 is a factory 3.07 build it would have the correct VSS for the change. All other '89 A4 builds use a driven less than 40 tooth and the VSS needs to be either changed or some mention rotating it 180*. That requires being creative with the retainer. I have never attempted the 180* rotation personally. Will it work? Maybe?
Without changing the drive gear to a 15 tooth it would require a driven in the 49 or 50 tooth range. There isn't such an animal out there!
What is the axle ratio as recorded on the RPO list?
Without changing the drive gear to a 15 tooth it would require a driven in the 49 or 50 tooth range. There isn't such an animal out there!
What is the axle ratio as recorded on the RPO list?
Team Owner
Joined: Sep 2003
Posts: 25,397
Likes: 2,741
This drive gear 8642620 (15 tooth), the 45 tooth driven and your present VSS should do the calibration.
Do everything the same time you do the gear swap. While doing all of this you'll need to remove the trans extension housing and it would be the appropriate time to do an extension bushing if your car is a "higher miler"! You'll need the bushing, extension housing to case seal, the extension output seal and a new seal for your VSS.
Do everything the same time you do the gear swap. While doing all of this you'll need to remove the trans extension housing and it would be the appropriate time to do an extension bushing if your car is a "higher miler"! You'll need the bushing, extension housing to case seal, the extension output seal and a new seal for your VSS.
Melting Slicks
Joined: Jun 2002
Posts: 2,152
Likes: 243
From: Northern VA
This drive gear 8642620 (15 tooth), the 45 tooth driven and your present VSS should do the calibration.
Do everything the same time you do the gear swap. While doing all of this you'll need to remove the trans extension housing and it would be the appropriate time to do an extension bushing if your car is a "higher miler"! You'll need the bushing, extension housing to case seal, the extension output seal and a new seal for your VSS.
Do everything the same time you do the gear swap. While doing all of this you'll need to remove the trans extension housing and it would be the appropriate time to do an extension bushing if your car is a "higher miler"! You'll need the bushing, extension housing to case seal, the extension output seal and a new seal for your VSS.
Dave, you are the parts guru!!!!
Team Owner
Joined: Sep 2003
Posts: 25,397
Likes: 2,741
You'll still need to change to the 15 tooth "drive" and I'd leave the 42 tooth driven in there IF that's what you find there. This is assuming you're using a 275 - 315 / 17 or something that shares it's diameter (25.6").
Team Owner
Joined: Sep 2003
Posts: 25,397
Likes: 2,741
I'd be very tempted to try a 45 tooth gear with the drive gear (17) that should be in your car presently. Your tire is something near 26" and you might be pretty close. If it's "fast" there's no further you can go to correct it "down" with out changing the "drive" gear but if it were "slow" you could start by changing out to a 44.
You're in a ery good position because your starting with a "hard to find" VSS that will accomodate the 40 + tooth gears!
You're in a ery good position because your starting with a "hard to find" VSS that will accomodate the 40 + tooth gears!
