Slow speedometer
Thread Starter
Burning Brakes
Joined: Oct 1999
Posts: 1,016
Likes: 1
From: Maine
Slow speedometer
My speedometer is as much as 10-15 MPH slow Does not bounce around but is just slow. Would i check the green(370) gear in transmission first or would it be something else thanks
Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
Speedometer gears: You may have to change the drive gear, unless you can put a gear on the cable that will get you within 10% of being correct. There is a 3890575 small GM gear drive that was used to get a 4.56 to work with a 4.11 cable gear. Let me know if you need it.
ratio__tire size___drive gr_____driven gr_teeth_color
2.73__8.15-G70__3895494____3987918_18____brown
3.08__7.75 -15___3924098____3987918_18____brown
3.31__8.45-G70__3924098____3987919_19____natural
3.36__8.15-G70__3924098____3987920_20____blue
3.55__8.15-G70__3924098____3860344_21____red
3.70__8.15-G70__3924097____3860345_22____green
3.70__8.45-_____ 3924098____3860344_21____red
3.73__8.15-G70__3924097____3860345_22____green
3.73__F70______ 3924097____3860348_25____orange
4.10__8.15-G70__3924097____3860347_24____yellow
4.11__F70______ 3924097____3860348_25____orange
4.56__8.15-G70__3924097____3860345_22____green* uses 3890575 adapter
ratio__tire size___drive gr_____driven gr_teeth_color
2.73__8.15-G70__3895494____3987918_18____brown
3.08__7.75 -15___3924098____3987918_18____brown
3.31__8.45-G70__3924098____3987919_19____natural
3.36__8.15-G70__3924098____3987920_20____blue
3.55__8.15-G70__3924098____3860344_21____red
3.70__8.15-G70__3924097____3860345_22____green
3.70__8.45-_____ 3924098____3860344_21____red
3.73__8.15-G70__3924097____3860345_22____green
3.73__F70______ 3924097____3860348_25____orange
4.10__8.15-G70__3924097____3860347_24____yellow
4.11__F70______ 3924097____3860348_25____orange
4.56__8.15-G70__3924097____3860345_22____green* uses 3890575 adapter
Instructor
Joined: May 2007
Posts: 140
Likes: 1
From: Louisville Colorado
I've got the same problem on my 57. From the best I can determine, my rear end has a 3.08 ratio. Does anyone know if the speedometer gears MagicV8 lists will work on a 57 (or a 58 - think my 3spd may have come from a 58)? Also, will a Chevy dealer still carry the gears?
Thanks
Thanks
Safety Car
Joined: Jun 2000
Posts: 4,711
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From: St. Louis MO
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Le Mans Master
Joined: Nov 2003
Posts: 5,772
Likes: 694
From: Maryland
St. Jude Donor '05, '09, '15
Don't mean to hijack this thread but I am confused. My M20 in the 65 appears to have only 5 teeth on the drive gear. 5 teeth is not an option on the web site listed. What am I missing? 
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Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
I've got the same problem on my 57. From the best I can determine, my rear end has a 3.08 ratio. Does anyone know if the speedometer gears MagicV8 lists will work on a 57 (or a 58 - think my 3spd may have come from a 58)? Also, will a Chevy dealer still carry the gears?
Thanks
Thanks
Burning Brakes
Joined: Dec 2006
Posts: 965
Likes: 3
From: St. Charles/Cave Creek IL/AZ
How about a Saginaw 3-speed?
I have a 1972 (or so) Saginaw 3-speed in another car that will probably need new speedo gears when I get it running.
Would the same drive/driven gear info hold true for that as well?
Thanks!
Would the same drive/driven gear info hold true for that as well?
Thanks!
Race Director
Joined: Jul 2002
Posts: 11,593
Likes: 173
From: Clayton NC
Besides the speedometer gear that is a possibility how about does your odometer work? If not this can cause a problem as the speedometer and the odometer are driven by the same assy. Dave
Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
Can't help you there - the 1973 Corvette parts manual only shows 3 speed parts up to 1970
Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
Thread Starter
Burning Brakes
Joined: Oct 1999
Posts: 1,016
Likes: 1
From: Maine
It does not work. You may have something here My 67 did not work either and i pulled the cluster and fixed it, i may have to do it again .i may be coming down your way pretty soon
Le Mans Master
Joined: Nov 2003
Posts: 5,772
Likes: 694
From: Maryland
St. Jude Donor '05, '09, '15
Not sure what came in the car but it has a 3.08 in it now. The driven gear is a brown 18 tooth and the tach reads around 2300@60mph. Tires are 255/60, 27" diameter. The speedo is only about 3 mph high to actual, checked with a GPS and a laptop. Does all that make sense?
