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#1
11-14-2014, 12:07 AM
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64 GTO Speedometer Gear
My 64 GTO was originally a 3.23 rear gear, but the previous owner changed it to a 3.90 gear. The speedometer worked fine before, but he changed the gear just before I got it, and now it does not work at all. He said something about the pitch of the gear being backwards. I have searched and found gears on the internet, but it talks about having the correct bore. I am not all that familiar with this aspect. Which exact gear do I need in my Muncie transmission ?
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#2
11-14-2014, 12:28 AM
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You have 2 gears. A drive gear and a driven gear. If it has the original trans then it should have a steel drive gear. If not you have to check the drive gear for wear. You also need to know the number of teeth. You then need to find the rear tire's rolling diameter (not the advertized diameter). From this you can figure the number of teeth you need on the DRIVEN gear. If there is not one available you can buy an adapter that changes the ratio between the driven gear and the speedometer.
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#3
11-14-2014, 10:38 AM
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hers's a site to calculate speedo gears and tire size.http://www.tciauto.com/tc/speedometer-gear-calculator/
Most likely have an eight tooth gear inside trans.
__________________
64 Lemans hardtop 4spd, buckets |
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#4
11-14-2014, 11:27 AM
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The driven gear can be changed/inspected relatively easily by pulling the cover off the transmission where the cable is attached. You can also see the drive gear when this cover is off to determine if it is damaged.
The driven gear can be changed by removing this cover and simply substituting a different gear. Changing the drive gear requires transmission disassembly. The 3.23 rear ratio uses an 8 tooth drive gear, the 3.90 uses a 6 tooth drive gear. The driven gear won't interchange between the two.There are only certain combinations of drive/driven that can be used. Look at the attached chart showing these combinations in the Chassis Manual. My Muncie has the 3.90 speedo gears that have never been changed since the car was new, but my GTO now has a 3.23 ratio rearend. The speedometer reads less than actual speed so I need to be careful of speed limits.
__________________
BONESTOCK GOATS '64 GTO Tripower Hardtop (Wife's Car) '64 GTO Tripower Post Coupe (My Car) '99 Bonneville SE Sedan |
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#5
11-14-2014, 11:34 AM
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__________________
Whistling past the graveyard. |
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#6
11-19-2014, 01:16 AM
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Speedometer Gear
I will have to check if the original gear is around in the parts I got with the car. I want to make it right eventually, but would rather have my speedometer be working, even if it does not read accurately. I am not even sure if my transmission is the original, but will check to see if the VIN is on it. I believe the previous owner also changed the insides of the Muncie, as it is now a close ratio, when it would have been a wide ratio. I have another complete 64 GTO engine with its original Muncie transmission. I may send to get the PHS, since the VIN is on the transmission. Someone mentioned a 6 tooth gear and a 8 tooth gear. If I look inside where the speedometer gear is, can I tell what rear end ratio was in that car that the engine and transmission came out of ?
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