My latest in a series of minor but non the less irritating problems is the fact that my spedometer does not work. I installed a new cable and confirmed that it worked from cable to gauge (I used a drill to test). I reconnected the cable to the transmission ( a very difficult job considering the tight spaces involved),after mating the gear (in this case, white)to the transmission. Took it out for a test drive and voila! It still doesn't work. I am really hesitant to go back in there because of the access difficulties (both under the car and under the dash)and my fore arms took quite a beating. Any idea what could be the problem? Should I just take it to a good mechanic and let him have at it? Or, is there a work around that I don't know of? Also, I have a 4:11 trans (327/350). Am I using the right gear (it's white)? Thanks again, to all. PS, Thanks once more to all who helped with my Holley Carb problem. The power valve replacemnt was the primary problem solver, a new set of points the secondary. The vette runs like a champ now and I think on my last test drive I pulled about 6 G's when I stomped on the pedal. SF/Keith
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Re: 65 SPEEDO PROBLEM
Keith, the plastic gear on the tailshaft of the trans is probably your problem. A '65 with the original 4.11 drivetrain should be using the yellow driven gear (24 teeth). I'm guessing that your "white" gear is what is referred to in the parts manual as "natural" with 19 teeth, which is halfway between the 18 tooth brown gear (for a 3.08 ratio) and 20 tooth blue (for a 3.36 ratio). These gears, as well as the 21 tooth red gear (for 3.55 ratios) all require the speedometer DRIVE gear # 3920498 (on the output shaft of the trans).
You trans should have the DRIVE gear # 3924097 (which has the same # of teeth, but set at a different angle and contact diameter) to mesh with the higher # of teeth found on the 22 tooth green (for 3.70 ratio) and your 24 tooth yellow 4.11. These gears are also slightly larger in diameter than for the 3.55 and below driven gears.
When you try to run below 21 tooth DRIVEN gears on this DRIVE gear, it barely contacts, then strips the plastic after a block or two of driving and stops turning.
The 19 tooth (natural), the 23 tooth (black), and the 25 tooth (orange) are to allow fine tuning of speedo reading with odd-ball size tires. 4.56 gear ratios are a whole different ball game, and I don't know the gear set combos. Neither can I tell you if these plastic gears are still available.
I hope that solves your problem -- once more with the scratched forearms. -
Re: 65 SPEEDO PROBLEM
Keith, the plastic gear on the tailshaft of the trans is probably your problem. A '65 with the original 4.11 drivetrain should be using the yellow driven gear (24 teeth). I'm guessing that your "white" gear is what is referred to in the parts manual as "natural" with 19 teeth, which is halfway between the 18 tooth brown gear (for a 3.08 ratio) and 20 tooth blue (for a 3.36 ratio). These gears, as well as the 21 tooth red gear (for 3.55 ratios) all require the speedometer DRIVE gear # 3920498 (on the output shaft of the trans).
You trans should have the DRIVE gear # 3924097 (which has the same # of teeth, but set at a different angle and contact diameter) to mesh with the higher # of teeth found on the 22 tooth green (for 3.70 ratio) and your 24 tooth yellow 4.11. These gears are also slightly larger in diameter than for the 3.55 and below driven gears.
When you try to run below 21 tooth DRIVEN gears on this DRIVE gear, it barely contacts, then strips the plastic after a block or two of driving and stops turning.
The 19 tooth (natural), the 23 tooth (black), and the 25 tooth (orange) are to allow fine tuning of speedo reading with odd-ball size tires. 4.56 gear ratios are a whole different ball game, and I don't know the gear set combos. Neither can I tell you if these plastic gears are still available.
I hope that solves your problem -- once more with the scratched forearms.Comment
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Re: 65 SPEEDO PROBLEM
Keith----
The fact that you've tested the cable and speedometer with an electric drill to confirm satisfactory operation of these components pretty much guarantees that your problem is with the speedomter driven or drive gear at the transmission end. There are several possibilities, including the ones that Wayne Midkiff mentioned. First, though, there is a possibility that the cable recepticle in the speedometer driven gear has stripped out, allowing the gear to turn while the cable does not. No matter, though, because I believe that you have the wrong driven gear, anyway.
As far as the correct part numbers go, I'm going to differ a bit with Wayne. First off, speedometer drive gears GM# 3924097 and GM# 3924098 were discontinued many years ago and replaced by GM #6261795 and GM #6261794, respectively. All of these speedometer DRIVE gears(mounted internally on trans mainshaft)are 8 tooth plastic gears and, if your transmission is original, were not installed in your trans. These gears were used on later design Muncies and require a special retainer, GM #1373122, which fits into a special groove on the later design (68+) mainshafts. Replacement of the speedometer DRIVE gear requires removal from the car and disassembly of the transmission. But, fortunately, I don't think you'll have to go that far.
If your transmission and 4.11:1 differential are original to your car and you are using stock diameter tires, you require the following:
1) speedometer DRIVE gear GM #3708145. This is an 8 tooth steel gear which presses onto the mainshaft. It usually gives no trouble since it meshes with a plastic driven gear. IF your transmission is original, this is what it should contain.
2) speedometer DRIVEN gear GM #3860347. This is a 24 tooth plastic gear color-coded "yellow".
As I have mentioned, this is what your Corvette requires and should have IF the transmission and differential are original and if the tires used are the same(or nearly the same)diameter as stock. Both the GM# 3708145 DRIVE gear and the GM# 3860347 DRIVEN gear are still available from GM. As Wayne advises, there are no GM-supplied "white" color-coded driven gears used for manual transmissions. The "natural" color coded gear, GM #3987919, has 19 teeth, but is incorrect for your car. The only "white" color-coded gear that I am aware of is a TurboHyromatic gear of 36 tooth configuration, GM #1359270, but I don't think that this gear will fit into a manual trans.In Appreciation of John HinckleyComment
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Re: 65 SPEEDO PROBLEM
Keith----
The fact that you've tested the cable and speedometer with an electric drill to confirm satisfactory operation of these components pretty much guarantees that your problem is with the speedomter driven or drive gear at the transmission end. There are several possibilities, including the ones that Wayne Midkiff mentioned. First, though, there is a possibility that the cable recepticle in the speedometer driven gear has stripped out, allowing the gear to turn while the cable does not. No matter, though, because I believe that you have the wrong driven gear, anyway.
As far as the correct part numbers go, I'm going to differ a bit with Wayne. First off, speedometer drive gears GM# 3924097 and GM# 3924098 were discontinued many years ago and replaced by GM #6261795 and GM #6261794, respectively. All of these speedometer DRIVE gears(mounted internally on trans mainshaft)are 8 tooth plastic gears and, if your transmission is original, were not installed in your trans. These gears were used on later design Muncies and require a special retainer, GM #1373122, which fits into a special groove on the later design (68+) mainshafts. Replacement of the speedometer DRIVE gear requires removal from the car and disassembly of the transmission. But, fortunately, I don't think you'll have to go that far.
If your transmission and 4.11:1 differential are original to your car and you are using stock diameter tires, you require the following:
1) speedometer DRIVE gear GM #3708145. This is an 8 tooth steel gear which presses onto the mainshaft. It usually gives no trouble since it meshes with a plastic driven gear. IF your transmission is original, this is what it should contain.
2) speedometer DRIVEN gear GM #3860347. This is a 24 tooth plastic gear color-coded "yellow".
As I have mentioned, this is what your Corvette requires and should have IF the transmission and differential are original and if the tires used are the same(or nearly the same)diameter as stock. Both the GM# 3708145 DRIVE gear and the GM# 3860347 DRIVEN gear are still available from GM. As Wayne advises, there are no GM-supplied "white" color-coded driven gears used for manual transmissions. The "natural" color coded gear, GM #3987919, has 19 teeth, but is incorrect for your car. The only "white" color-coded gear that I am aware of is a TurboHyromatic gear of 36 tooth configuration, GM #1359270, but I don't think that this gear will fit into a manual trans.In Appreciation of John HinckleyComment
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Re: 65 SPEEDO PROBLEM
Joe/Wayne, Thanks for your response. I took the vette into my mechanic today armed with your advice. After checking it out, his diagnosis is a loose drive gear in side the transmission. It is in fact a steel gear (you can see it with the nipple housing out). Unfortunately, shop owner wants to charge me around three hundred dolars to take care of the problem-and I am already overbudget and don't need another cost over run on the domestic front. I will therefore drop the transmission myself and then take it to someone to repair if it is too complicated for me to do alone. Any tips on dropping the trans? It doesn't look overly hard, just time consuming. Also, should I just try the correct "yellow" gear just in case that is really the problem? I don't see how the drive gear could come loose-but I guess anything can happen. On further reflection, the spedometer used to work (several years ago) and it stopped all of a sudden. I heard a slight "ping" and that is why I thought it was the cable originally. Could something have broken inside the transmission? Thanks again, KeithComment
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Re: 65 SPEEDO PROBLEM
Joe/Wayne, Thanks for your response. I took the vette into my mechanic today armed with your advice. After checking it out, his diagnosis is a loose drive gear in side the transmission. It is in fact a steel gear (you can see it with the nipple housing out). Unfortunately, shop owner wants to charge me around three hundred dolars to take care of the problem-and I am already overbudget and don't need another cost over run on the domestic front. I will therefore drop the transmission myself and then take it to someone to repair if it is too complicated for me to do alone. Any tips on dropping the trans? It doesn't look overly hard, just time consuming. Also, should I just try the correct "yellow" gear just in case that is really the problem? I don't see how the drive gear could come loose-but I guess anything can happen. On further reflection, the spedometer used to work (several years ago) and it stopped all of a sudden. I heard a slight "ping" and that is why I thought it was the cable originally. Could something have broken inside the transmission? Thanks again, KeithComment
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Re: 65 SPEEDO PROBLEM
Keith, by all means get a second opinion, or check the drive gear for slippage yourself. Like you, I've never heard of these coming loose -- have you seen the puller used to remove this part ? This gear sits all by itself, and its only job is to drive the little colored plastic driven gear. If there is a problem of fit, the plastic gear is sacrificed. Yes, I'd try the yellow driven gear, but while you have the "nipple" assembly out, see if the drive gear moves by prodding with a soft metal punch. If it's loose on the mainshaft, then put back the "natural" gear that you had in before and calculate speed with a table of RPM versus speed in each shifter position, taped to the dash, until you get around to pulling the trans.
Mea culpa for the wrong driven gear part #. The main point for others following this post is (for the years '63 - '67) there are 2 different 8-tooth steel drive gears; one for diff. ratios 3.08 to 3.55, and another for 3.70 and 4.11. For those with 4.56 rear ends, there is a third drive gear (6 teeth), which couples with a 20 tooth driven gear, which is not plastic, but steel. As well, there are 4 different colored DRIVEN gears used for ratios up to and including 3.55, as well as 4 different ones for 3.70 and 4.11 gearsets (but you can't use them in a trans with the drive gear intended for the lower numerical ratios). So if your speedo is reading low, try the driven gear with the next lower # of teeth, and vice-versa.Comment
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Re: 65 SPEEDO PROBLEM
Keith, by all means get a second opinion, or check the drive gear for slippage yourself. Like you, I've never heard of these coming loose -- have you seen the puller used to remove this part ? This gear sits all by itself, and its only job is to drive the little colored plastic driven gear. If there is a problem of fit, the plastic gear is sacrificed. Yes, I'd try the yellow driven gear, but while you have the "nipple" assembly out, see if the drive gear moves by prodding with a soft metal punch. If it's loose on the mainshaft, then put back the "natural" gear that you had in before and calculate speed with a table of RPM versus speed in each shifter position, taped to the dash, until you get around to pulling the trans.
Mea culpa for the wrong driven gear part #. The main point for others following this post is (for the years '63 - '67) there are 2 different 8-tooth steel drive gears; one for diff. ratios 3.08 to 3.55, and another for 3.70 and 4.11. For those with 4.56 rear ends, there is a third drive gear (6 teeth), which couples with a 20 tooth driven gear, which is not plastic, but steel. As well, there are 4 different colored DRIVEN gears used for ratios up to and including 3.55, as well as 4 different ones for 3.70 and 4.11 gearsets (but you can't use them in a trans with the drive gear intended for the lower numerical ratios). So if your speedo is reading low, try the driven gear with the next lower # of teeth, and vice-versa.Comment
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Re: 65 SPEEDO PROBLEM
Keith----
I agree with Wayne. I don't see how the speedometer drive gear could come loose on the shaft. I could easily understand it if you had a 68+ with the plastic drive gear and metal retainer---many folks don't know about the retainer and might install the gear(which is a slight interference fit on the shaft)without the retainer. However, as I mentioned and as you've apparently confirmed, mid years use a steel drive gear. This gear is a somewhat heavy press fit and I can't see it being dislodged or damaged by the plastic driven gear. As Wayne suggested, check this gear by trying to move it with a screwdriver or punch while the trans is still in the car. It is possible, however, that the gear was never installed properly and is positioned incorrectly on the shaft. It is possible to do this, but, usually, a slight variation doesn't cause problems.
After checking the drive gear for obvious problems as described, I'd try installing the correct driven gear that I mentioned earlier; these gears aren't very expensive, so you don't have a lot to lose.In Appreciation of John HinckleyComment
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Re: 65 SPEEDO PROBLEM
Keith----
I agree with Wayne. I don't see how the speedometer drive gear could come loose on the shaft. I could easily understand it if you had a 68+ with the plastic drive gear and metal retainer---many folks don't know about the retainer and might install the gear(which is a slight interference fit on the shaft)without the retainer. However, as I mentioned and as you've apparently confirmed, mid years use a steel drive gear. This gear is a somewhat heavy press fit and I can't see it being dislodged or damaged by the plastic driven gear. As Wayne suggested, check this gear by trying to move it with a screwdriver or punch while the trans is still in the car. It is possible, however, that the gear was never installed properly and is positioned incorrectly on the shaft. It is possible to do this, but, usually, a slight variation doesn't cause problems.
After checking the drive gear for obvious problems as described, I'd try installing the correct driven gear that I mentioned earlier; these gears aren't very expensive, so you don't have a lot to lose.In Appreciation of John HinckleyComment
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Re: 65 SPEEDO PROBLEM:SUCCESS!
To Joe L and Wayne M, gentlemen, allow me to extend my thanks for your guidance and detailed analysis of the difficulties with my spedometer problem. It was in fact, the driven gear that was the problem. I put the one with the correct teeth and it now works just fine (although the replacement driven gear was black (however, it looked like it had been painted black over yellow-who knows)-I also put in a new nipple as the one I had was rusting and leaking a little. In any case, that solved the problem. Thansk also to Bill W., who gave me a detailed description on how to drop the tranny. Fortunately, I did not have to do so this time, but I will keep his description on file for reference. Again, thanks to all.Comment
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Re: 65 SPEEDO PROBLEM:SUCCESS!
To Joe L and Wayne M, gentlemen, allow me to extend my thanks for your guidance and detailed analysis of the difficulties with my spedometer problem. It was in fact, the driven gear that was the problem. I put the one with the correct teeth and it now works just fine (although the replacement driven gear was black (however, it looked like it had been painted black over yellow-who knows)-I also put in a new nipple as the one I had was rusting and leaking a little. In any case, that solved the problem. Thansk also to Bill W., who gave me a detailed description on how to drop the tranny. Fortunately, I did not have to do so this time, but I will keep his description on file for reference. Again, thanks to all.Comment
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