1968 speedo to fast
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Le Mans Master
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From: Loveland
1968 speedo to fast
In my 1968 4 speed M20. The speedometer reads to fast. I think it's because of the tires. I have checked it against a GPS. Is the stock driven speedo gear a 22 tooth? Seems I need the 23 tooth to slow it down about 2.5 MPH. Will the 23 tooth driven gear install correctly? I'm not sure what drive gear I have
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Yes it will, pull the speedometer head out of the tranny and count the teeth. If the driven gear doesn't come out, just reach in with some needle nose pliers and pluck it out. If you figure out your rear end ratio you can find the right driven gear for your tranny
Last edited by Rescue Rogers; Nov 5, 2019 at 12:18 PM.
Thread Starter
Le Mans Master
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From: Loveland
I can remove the driven gear quite easy. If it's a 22 tooth and I can slide a 23 tooth in smoothly, is there any danger of destroying the drive gear? I don't really want to remove the trans to fix the drive gear. At about 2 MPH to high,, I know 1 tooth larger will slow it down about that much. I don't need to go through the rear end ratio figures.
The 22 tooth driven gear was paired with the 1.78,,,, OR the 1.84 drive gear. If I have a 1.84 inch drive gear I am worried it wont take the 23 tooth driven. If it is a 23 tooth driven,,,, it only was paired with the 1.84 in. drive gear, so it would take a 24 tooth driven gear no problem.
Looked up the color,,, I have the black driven gear,,, it's the 23 tooth,, paired with the 1.76 drive gear. So I think I can go to a 24 tooth driven. Only the 22 tooth gear comes in 2 different OD .81 and .87,,,, But 2 different colors,,, gray,,, and green.
The 22 tooth driven gear was paired with the 1.78,,,, OR the 1.84 drive gear. If I have a 1.84 inch drive gear I am worried it wont take the 23 tooth driven. If it is a 23 tooth driven,,,, it only was paired with the 1.84 in. drive gear, so it would take a 24 tooth driven gear no problem.
Looked up the color,,, I have the black driven gear,,, it's the 23 tooth,, paired with the 1.76 drive gear. So I think I can go to a 24 tooth driven. Only the 22 tooth gear comes in 2 different OD .81 and .87,,,, But 2 different colors,,, gray,,, and green.
- 17 tooth purple dimension -1.75 x .305 x .810
- 18 tooth brown dimension -1.75 x .305 x .810
- 19 tooth white dimension -1.75 x .305 x .810
- 20 tooth blue dimension -1.75 x .305 x .810
- 21 tooth red dimension -1.75 x .305 x .810
- 22 tooth grey dimension -1.75 x .305 x .810
- 17-22T .810 diameter gears must be used with a 1.84 OD speedo drive gear.
- 22 tooth green dimension -1.75 x .305 x .870
- 23 tooth black dimension -1.75 x .305 x .870
- 24 tooth yellow dimension -1.75 x .305 x .870
- 22-24T .870 diameter gears must be used with a 1.76 OD speedo drive gear
Last edited by kodpkd; Nov 5, 2019 at 03:17 PM.
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The black 23 tooth gear, according to the parts book, is 3860346.
That gear was only used with a 4.56:1 rear end.
The yellow 24 tooth gear, 3860347, was also used with the 4.56:1 rear end.
Based on your chart above both the black and yellow use the same drive gear.
That gear was only used with a 4.56:1 rear end.
The yellow 24 tooth gear, 3860347, was also used with the 4.56:1 rear end.
Based on your chart above both the black and yellow use the same drive gear.
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If its a 68 tranny, the drive gear is pressed on steel gear. Some of the late 70's trannys used a plastic drive gear that used a clip to hold it in place. You should be fine, if it didnt work the drive gear would just eat the plastic driven gear.
Thread Starter
Le Mans Master
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From: Loveland
Well I was wrong. I just looked at the end of the driven gear,,,, I thought it was black,, 23 tooth gear. Nope. I have a 3.27 rear end,,,, with a 19 tooth white gear. I.m ordering a blue 20 tooth gear to slow down my speedo. I did count the drive shaft turns with 1 turn of the wheel. 3.30ish. It says with that rear end I should have a 7 or 8 tooth drive gear. Yep,,,, I should have taken the driven gear out to look. Oh well,,, now I have an extra 24 tooth driven gear.
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Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,216
Likes: 9,354
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist