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Discussion Starter #1
I have my Muncie apart and I wanted to put the right drive and driven gear combination in to make the speedometer work again. I have read that most Muncies have 8 tooth drive gears, but how do you know? If I count what I think are teeth, I don't get 8. I get 6. I have never heard of a 6 tooth drive gear. There are no painted marks on it either. So, how do you count the number of teeth on a worm gear?
 

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Here, try this link to start. There are some good web sites that will help you calculate what the correct number of teeth on both the drive and the driven gear should be. The hardest part for me was actually finding the drive gear I wanted.
http://www.camaros.net/forum/Forum9/HTML/008890.html

ps. You can usually fine tune your speedometer calibration by changing just the driven gear. I would try to avoid messing with the drive gear unless you have to.
 

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Discussion Starter #3
I think that you may have misunderstood my question. I have seen the calculation programs and the formulas, but they do you no good unless you know how many teeth the drive gear has on it. That's what I am trying to figure out. If I know what drive gear I have, I can figure out what driven gear I need to go with it. Is there any special trick to counting the teeth on a worm gear. If I count across it, I get six teeth, but I have never heard of a 6 tooth drive gear.
 

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Cameron
It's probably an 8 tooth. There are only 8 & 9 tooth drive gears commmonly used on Muncies.
Just start to count the teeth from the left where one tooth begins, and go across. What ever you end up with is the number.
I have a list of driven gear part numbers and colors as well. Let me know if you need them.
Jim
 

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Discussion Starter #5
Jim,

I would love to see the list of all the gears. My drive gear has no color at all, it is metal.

If I start where one tooth begins and count straight across, I get six teeth. If I start where the tooth begins and count diagonally to where it ends, I get 7 teeth. I think that I have a 7 tooth drive gear, but I'm not for sure.
 

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try counting around it instead of across it. use a sharpie or something to mark the first one, and just count clockwise around the outside of the gear.

------------------
1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik
 

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Discussion Starter #7
OK, that makes sense. I have a seven tooth drive gear.
 

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In Ricks they are color coded and they give you a good idea of which to use. They give you the qty of teeth on the speedo gear (in the transmission) that corresponds to the gears in the rearend of the car. Page 86.

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1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers
 

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Cameron
Four speed Muncies used an eight tooth or a nine tooth Steel gear, except the 74 - 9 tooth gear was plastic. In 75 and 76 Borg Warner used a 7 tooth.

Drive Gears
67-70 Muncie 8-tooth 1-27/32OD X 39/64 thick #3708144

67-70 Muncie 8-tooth 1-3/4OD X 17/32 thick #3708145

67-69 Muncie 9-tooth 1-27/32OD X 39/64 thick #3905494

1970 all 4-speed Heavy Duty Muncie with 454 Engine 8 tooth #3978758

1974 Muncie 9-tooth plastic green #6261782

Driven Gears
18-tooth #3987918 brown

19-tooth #3987919 natural

20-tooth #3987920 blue

21-tooth #3987921 red

22-tooth #3860345 green

23-tooth #3860346 black

24-tooth #3860347 yellow

25-tooth #3860348 orange

If you like, just give me your tire height and rear end ratio and I'll tell you what gear to use with a 8 or 9 tooth drive gear.
Jim



[This message has been edited by GMJim (edited 11-19-2002).]

[This message has been edited by GMJim (edited 11-19-2002).]
 

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Discussion Starter #10
Jim,

I have 26.1" diameter tires and 3.42 rear gears. I believe that this works out with an 8 tooth drive gear and a 21 tooth driven gear. I originally thought that I had an 8 tooth drive gear. Now that I have the tranny apart, I found a 7 tooth gear. That explains why the speedometer was reading slow.

Will the 8 tooth drive gear work with the 21 tooth (red) driven gear? I read somewhere that only about half of the driven gears will work with an 8 tooth drive gear and the rest of the driven gears will work with either a 7 or an 9 tooth (I can't remember)drive gear. Can anyone confirm this? I have an early tailhousing that has the speedometer drive output located on the driver's side of the transmission, not the passenger's side like later Muncies.
 

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Based on the info you gave me. Your speedo drive ratio is 2.64689. The best combonation for speedo gears are 8 tooth drive gear with a 21 tooth Red driven gear OR a 9 tooth drive gear with a 24 tooth Yellow driven gear.
Jim
 

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Discussion Starter #12
Jim,

So the 8 tooth drive gear will mesh correctly with the 21 tooth, red, driven gear?

------------------
69 Camaro
400 Small Block
Trick Flow Heads
Comp 282S solid cam
Performer RPM intake
750 CFM Holley
and a Muncie four speed
Pics of My Car
 

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Cameron
The short answer is, Yep! However. Your ratio is 2.64689 or 2.65 If you use a an 8 tooth drive gear and a 21 tooth red driven gear you get a 2.625 ratio. If you use a 9 tooth drive gear and a 24 tooth yellow driven gear, you get a 2.666 final ratio which is closer. I'm just giving you the detailed ratios so that you can make a decision. If you already have an 8 tooth drive gear, use a red 21 tooth gear. Between tire pressures fluctuating and 60's technology for speedos you won't be able to see a difference. The accuracy will be more than exceptable.
Jim

If anyone is interested, I will make up a chart along with a simple and a VERY detailed formula to print out, on the speedo drive ratios. And all the drive and driven gears.
All I need Is for somebody to help me figure out how to attach a file to the post. I'm good with computers, but not with software.
Jim

[This message has been edited by GMJim (edited 11-20-2002).]
 

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Discussion Starter #14
I have looked everywhere for an 8 tooth drive gear for my transmission, but I have had no luck. I already have a 1.84" (1 27/32") OD, 7 tooth drive gear. I don't know how it got there or where it came from, but that is what I have. With my tire and rear gear ratio, the calculator on TCI's web site says that I need an 18.48 tooth driven gear. Obviously, nobody makes an 18.5 tooth driven gear so I will need either an 18 or 19 tooth driven gear. I would prefer that the speedometer read a little faster than I am really going so I would prefer to use the 18 tooth driven gear. Will my 1.84 OD drive gear and an 18 tooth driven gear work together correctly? If it won't, will the 19 tooth work? I believe that I have the larger OD drive gear that I think works with the smaller driven gears.
 

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Discussion Starter #15
Decided to start new thread on the above question, please see it.
 
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