Speedometer Gear Issue
Thread Starter
Racer
Joined: Apr 2009
Posts: 331
Likes: 44
From: Cincinnati Ohio
Speedometer Gear Issue
I have been struggling with the Speedometer on my 73. 4 speed car. Old speedometer broke needle due to bouncing. Replaced cable and needle and the replacement needle came off. Speedo was also howling like no lubricaton. Lubed speedo. Pushed it back on and it did it again so I bought a new repo speedometer. So far new speedo had chewed up 2 driven gears. Looks like not getting full tooth engagement. Speedometer, cable and right angle gear box all turn freely with fingers. Speedometer works fine with electric drill and for about 100 miles of driving then the driven (pencil) gear ends up with tops of teeth worn off. Other than tearing tailshaft apart, is there any way to check which drive gear is in the transmission? From the looks of it wondering if the transmission has a small diameter drive gear and I have put in the driven gears for a large diameter drive gear. Don't know if this is even possible. Would appreciate any information. Thanks in advance for any help!
Last edited by RU7376vettes; Jun 14, 2020 at 11:22 PM.
Race Director
Joined: Nov 2006
Posts: 13,229
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
Had an issue years ago, simular issue. Turns out I wasn't getting the gear into the trans deep enough. It looks like the retaining clip goes here, but in reality, it goes in the next grove up if that makes any sense at all.
I tore up 2 gears before I realized my mistake.
I tore up 2 gears before I realized my mistake.
Melting Slicks
Joined: Feb 2018
Posts: 2,326
Likes: 721
From: Marietta GA
On my 73 SB the bouncing (at times) speedo decided to quit. I know about removing the Instrument cluster (cruel and unusual punishment), so I figure, just use the tach to Guess-T-Mate my speed. Of course the tach dies the very next day. After testing the speedo cable with a drill (turning in REVERSE, I knew the gear in the 4 speed tranny was toast. After a few sleepless nights, I realized that me touching the distributor, would end up with a big tow charge to the Corvette Service Shop. I took the car to a shop that is part of a large Corvette sales operation. They installed a new gear at the tranny, and replace the 90 degree adapter on the distributor. After the 20 the mile drive home, the speedo quit. When I returned the next week, they put my car on a lift and removed the gear, it was chewed up. The Service Manager explained that the tranny had to be removed to replace the gear/part where the Plastic Gear is inserted. I said ok, and of course, and “The while I am there” kicks in for a ... tranny rebuild, new clutch, flywheel, and water pump (that had been leaking). If your new plastic gear got chewed up, then it may be inside gear on the your tranny. Except for the ever present leaking, my tranny was working great. I hope this helps, Good Luck.
Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
I have been struggling with the Speedometer on my 73. 4 speed car. Old speedometer broke needle due to bouncing. Replaced cable and needle and the replacement needle came off. Speedo was also howling like no lubricaton. Lubed speedo. Pushed it back on and it did it again so I bought a new repo speedometer. So far new speedo had chewed up 2 driven gears. Looks like not getting full tooth engagement. Speedometer, cable and right angle gear box all turn freely with fingers. Speedometer works fine with electric drill and for about 100 miles of driving then the driven (pencil) gear ends up with tops of teeth worn off. Other than tearing tailshaft apart, is there any way to check which drive gear is in the transmission? From the looks of it wondering if the transmission has a small diameter drive gear and I have put in the driven gears for a large diameter drive gear. Don't know if this is even possible. Would appreciate any information. Thanks in advance for any help!
Intermediate
Joined: Mar 2020
Posts: 28
Likes: 9
Same problem with my 78 4 speed, I replaced almost everything then figured out that the bullet shaped part that the speedometer gear went in was worn out, i put a new one and new gear , its been working over a year, beleive it or not the plastic gear wore out the aluminum, the new part was made of steel, I had replaced cable, both gears, and it was a simple fix.
Thread Starter
Racer
Joined: Apr 2009
Posts: 331
Likes: 44
From: Cincinnati Ohio
Spent part of the day taking closer look at the drive gear. Put borescope on it and the gear looks great. When I put finger in hole the drive gear spins on the output shaft but I can't get it to slide front to back. Since it is a Muncie from wha tI can read it should be pressed on. I will find out shortly as the transmission is coming out, I have a Tremec TKO600 on order. This one must have figured out it was being replaced and decided to hassle me. I appreciate everyone's help, I will tear into it when I get the transmission out. I really want to know why that drive gear is spinning and if there was a miss match of drive to driven gear sizes. Thanks again all for your comments. More to come when the Tremec arrives, in the meantime I a going to drive it and have calculated speeds versus tach readings.
Last edited by RU7376vettes; Jun 15, 2020 at 05:38 PM.
Racer
Joined: Jan 2017
Posts: 496
Likes: 153
From: San Francisco Bay Area
Spent part of the day taking closer look at the drive gear. Put borescope on it and the gear looks great. When I put finger in hole the drive gear spins on the output shaft but I can't get it to slide front to back. Since it is a Muncie from wha tI can read it should be pressed on. I will find out shortly as the transmission is coming out, I have a Tremec TKO600 on order. This one must have figured out it was being replaced and decided to hassle me. I appreciate everyone's help, I will tear into it when I get the transmission out. I really want to know why that drive gear is spinning and if there was a miss match of drive to driven gear sizes. Thanks again all for your comments. More to come when the Tremec arrives, in the meantime I a going to drive it and have calculated speeds versus tach readings.
Melting Slicks
Joined: Feb 2018
Posts: 2,326
Likes: 721
From: Marietta GA
RU
I think you are correct about the internal gear in the Muncie. My service folks use a retired gentleman to rebuild trannys. The only charge from him was the standard $ 250 that included the seals, if there were any other parts needed, believe me, I would have been charged.
I think you are correct about the internal gear in the Muncie. My service folks use a retired gentleman to rebuild trannys. The only charge from him was the standard $ 250 that included the seals, if there were any other parts needed, believe me, I would have been charged.
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