The "driven" gear(plastic) that fits into the transmission, where the speedo cable goes, isn't making correct contact with the tranny driving gear. It looks like the teeth are not meshing all the way which means my speedometer is not working. My gauge has been replaced because it was shot, I have a new cable, and a new plastic gear,.but the speedo, as mentioned before, isn't working. So, what's the solution? Are their slightly larger plastic gears or do I just have the wrong one and, if so, where do I buy one? Thanks for your help. :)

 

You didn't provide enough information, as it may depend on the color of the driven gear you took out, as compared to the color of the gear you are putting in, and whether you changed the gear ratio of your differential (ie, the whole differential, or the gearset).

I'm not especially knowledgeable, but I do know there were two different drive gears used in the transmission, depending on the ratio of the differential that the tranny was mated to at the factory. I think there was a slight overlap, but I'm not certain of the cutoff ratio that required the driving gear change...probably around 3:55/1.

One driving gear uses a green (22-tooth), black (23-tooth) or yellow (24-tooth) driven gear.

The other requires a brown (18-tooth), natural (19-tooth), blue (20-tooth, red (21-tooth), or silver (22-tooth) driven gear.

If you changed the differential ratio and you now need the 23 or 24-tooth driven gear and it isn't meshing properly, then you'll have to change the driving gear, if it's still available.

Likewise if you were trying to install a 19, 20, or 21-tooth gear, then you also have the wrong driving gear for those driven gears.

If you were installing a 22-tooth gear, you can buy the one of the different color (ie, green versus silver) than the one you have.


Corvette Central (and probably other Covette parts vendors) sells the driven gears. GM, and perhaps tranny rebuilders, may have the driving gears if they are still available.


[Modified by waynec, 9:36 PM 10/24/2003]

 

motro,

One drive gear in the tranny was for 3.08 to 3.55 =Brn. Nat. Blu. Red silver Just for ref. we'll call this group 1
Other drive gear in the tranny was for 3.70 to 4.56 =Grn. Blk. yell. org. Just for ref. we'll call this group 2

If you know the color thats not meshing, most likely you need to try one of the other color groups. Also, I would crawl under the diff and get the gear ratio so you can make the speedo happy. Now if your lucky, you will have the ratio of the other color group you need to be in, so you can get this meshing thing to happen.
Craig :)


[Modified by Cmacsvette, 6:05 PM 10/25/2003]

 

Thanks guys. I thought I had a 3:55 but, I really had a 3:36! So, I'll order the correct gear. BTW, Corvette Central has a "steel" gear. Any advantage?

 

The gear I took out of my 1967 with 3.36:1 was 20 teeth. I had to compensate for 215-70R/15 tires compared to the original 7.75/15s. My speedo was reading 70mph at an actual 60mph. I went to 22 teeth and the problem was solved. I do have the 23 tooth gear but it is a different size as is 24. That may be your problem: you may have to change the drive gear as well. The gears are available from GM at about $5.00. This site was useful when I was diagnosing the needed number of teeth.
http://members.core.com/~faldrich/speedo.htm


[Modified by paul67, 9:21 AM 10/25/2003]

 

motro,
I think your getting your gears mixed up. The steel gear is the drive gear, this gear is in the tranny. The gear it drives is the nylon gear in your hand. It's the gear you install from the outside of the tranny into the little bullet housing, this is also the gear(nylon) that the end of your speedo cable fits into. As far as I know their still nylon. You will need to know which nylon gear color is not meshing, so what I'm saying is, no matter what color gear (tooth count) in the color group I mentioned above you put in there, it will not mesh. Ex. If you took out a blue and it's not meshing, then none of the other colors in that group will mesh. You would have to go to one of the other colors in the other color group and try it, meaning you have the other steel drive gear inside of the tranny. Now if you have a 3.36 rear and the steel drive gear inside of the tranny is for the, grn, blk., yell, org (nylon gear) your screwed, because your out of your gear ratio, meaning your speedo will still work, but will not be accurate. Remember, you also changed your tranny lately to a M22. Anybody else?
Craig :cheers:

 

Steel drive gear is for 4.11, 4.56, 4.88. All others, from 3.70 on down, use the plastic drive gear.

Joe

 

The 215/70R-15 and OE 7.75-15 bias plys have the EXACT same revolutions per mile figure of 775, so any change in speedometer gearing you had to make to bring the speedometer into reasonable accuracy had NOTHING to do with the 215/70R-15 tires.

Duke

 

I stand corrected.

 

Thanks everyone for the input. I've written to the guy who built my "rockcrusher" to see what drive gear he installed. Then, I'll be able to correctly match the drive gear. Again, thanks everyone!

 

If you don't have a correct drive gear installed that will accept a driven gear to reasoably calibrate your speedo with your installed axle and tire revs per mile, you could install any driven gear that will mate with the drive gear and use an external Stewart -Warner adapter to bring the speedo into reasonable calibration.

Changing the drive gear will require the gearbox to be removed and disassembled.

Duke