speedometer reading
Thread Starter
Heel & Toe
Joined: Mar 2010
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speedometer reading
Im having trouble diagnosing why I am not getting a reading on my speedo. I have a restored gage cluster, new cable, and rebuilt (by other) m20. Pencil gear looks good. I am replacing it anyway. My question is this. Can the circle gear in the tailshaft possibly be positioned wrong upon rebuild? Note, that when I first put everything back together, I was getting a 20 mph reading max. Removed pencil gear to inspect and reinstalled it, then had no reading. My next test is to attach the speedo cable to a hand drill to check the speedo.
Any ideas?
Any ideas?
Tech Contributor
Joined: May 2005
Posts: 15,575
Likes: 118
From: Conroe Texas
What year car do you have?
If the drive gear, and driven gear are not aligned, you won't have a working speedo.
If the drive gear (ring gear in your post) is not the proper one for the driven gear you are using, then the ring gear will eat the driven gear and the speedo will stop working after a while.
In some instances the drive gear is not pressed on the output shaft, but held on by a clip (1967 I think?) and if that clip comes loose the drive gear can move.
If the drive gear, and driven gear are not aligned, you won't have a working speedo.
If the drive gear (ring gear in your post) is not the proper one for the driven gear you are using, then the ring gear will eat the driven gear and the speedo will stop working after a while.
In some instances the drive gear is not pressed on the output shaft, but held on by a clip (1967 I think?) and if that clip comes loose the drive gear can move.
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
Which driven gear did you have installed when it worked? There are two size "families" of drive and driven gears that go together (large drive/small driven and small drive/large driven); if you have the small drive gear and a small driven gear, there won't be enough tooth engagement to work.
What tire size and rear axle ratio do you have?
Muncies had two diameters of pressed-on drive gears until '68, when the gears became a loose fit with the retainer clip, through 1970. '71-up Muncies used a larger output shaft, and only used the "large" drive gear.
What tire size and rear axle ratio do you have?
Muncies had two diameters of pressed-on drive gears until '68, when the gears became a loose fit with the retainer clip, through 1970. '71-up Muncies used a larger output shaft, and only used the "large" drive gear.
Thread Starter
Heel & Toe
Joined: Mar 2010
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Thanks for the response. I have 3:70 gears with standard 27" tires. As for the tranny, totally new, have no idea what was installed. I guess a good test at this point would be to try a large driven gear ans see what happens.
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
You might get lucky. 3.70 was the only ratio where GM had both "families" of drive and driven gears available for stock 27" tires.
With the "large" (1.85" O.D.) drive gear, a 3.70 used a "small" 22-tooth silver plastic driven gear, GM #3987922. With the "small" (1.77" O.D.) drive gear, a 3.70 used a "large" 22-tooth green plastic driven gear, GM #3860345.
With the "large" (1.85" O.D.) drive gear, a 3.70 used a "small" 22-tooth silver plastic driven gear, GM #3987922. With the "small" (1.77" O.D.) drive gear, a 3.70 used a "large" 22-tooth green plastic driven gear, GM #3860345.
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You can also check out this post
Hi , I had trouble and the forum members helped me
This post of mine and the responses may help you:
http://forums.corvetteforum.com/c1-a...-question.html
Jack
This post of mine and the responses may help you:
http://forums.corvetteforum.com/c1-a...-question.html
Jack
Thread Starter
Heel & Toe
Joined: Mar 2010
Posts: 20
Likes: 0
another thought......The speedo is a 64. The tranny tailshaft is from a 65. I had to buy the longer 65 cable since the speedo input was now on the opposite side. I hope I was correct in assuming the cable diameter at the speedo was the same for all C2s
Team Owner
Joined: Oct 2000
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From: Washington Michigan
