Transmission drive gear

[A1Avette79]

Speedo stopped working a while back - needle jumped for a couple days, then stopped working altogether. Finally got underneath and pulled the speedo cable off the transmission. The tip of the speedo cable had broken off and the nylon driven gear is scored and the sleeve is worn. I can't find any record from the previous owner to indicate that the gear was ever replaced. There is, however, a record of the speedo cable being replaced back in '93 (40,000 miles ago). Whoever did the work installed a single cable and bypassed the cruise control but I don't know if they replaced the gear or not so I don't know if the one that is installed now is original. The gear that is in now is a "natural" color 22 tooth. Either way something caused the speedo cable to fail after only 40,000 miles. I never checked my speedometer for accuracy before now - never thought about it until it stopped working.
When I checked on line to order a new driven gear I couldn't find a "natural" color 22 tooth gear - only a silver or gray one. I wanted to use one of the gear calculators on the internet to make sure the gear was correct before i buy a new one but i need to know the size of the metal drive gear to use the calculator. Unfortunately pulling the transmission out to look at the drive gear isn't an option.

Was there a standard size and tooth count metal drive gear used on a '79, automatic,L48 with a 3.55 rear end model (i am assuming i have a 3.55 rear since that was standard in '79)?

 

[Peer81]

You can see the drive gear from under the car without a problem. When you know the color you can calculate the correct combo.
Before putting the cable in I did lube it with grease.

Greetings Peter

 

[A1Avette79]

Thanks Peter. I've got the new one all lubed up and ready to go.
Are the metal drive gears color coded, too? The retaining bolt for the driven gear is painted green - would that mean the drive gears were also green?

 

[Peer81]

As far as I know the drive gear is also plastic and color coded. I don't think the color of the bolt is indicating you have a green drive gear.

Greetings Peter

 

[Vettehead Mikey]

Your AIM will tell you which tooth count and colour the driven gear should be. The on line calculators need to be given the original tire size that came on the car and NOT the size you're running now if you want to reverse calculate what GM used.

 

[A1Avette79]

Thanks Peter.
Mikey - I ran the calculator backwards using the original tire size - great idea, thanks.

 

[Peer81]

I did about the same I had a worn driven gear in and wanted the speedo to be spot on. First noted the driven gear color then put in a drive gear (not the right one). After that started testdriving with a navigationsystem with internal speedo. Compared the navi speed with the speedo at differend speeds (something like 20, 40 and 60 mph). After that you can calculate what the right drive gear should be. Mine is now spot on (1/2 mph difference) downside is you need to take out the drive gear twice.

If you want to do this, I can give you the best drive gear in combo with your driven gear within one day. Just let me know.

Greetings Peter

 

[A1Avette79]

Thanks Peter. I won't have time to crawl under the car until Saturday after next. I'll let you know what I find.
Trenton

 

[A1Avette79]

Got the new gear, sleeve and O-ring. I'll install it next weekend. Does the sleeve/gear need to be lubed before installation or does the Trans fluid serve as lube?

 

[Peer81]

Trans fluid will solve that problem. When you take out the sleeve some fluid will also come out

Greetings Peter

 

[A1Avette79]

Ok. Peter, thanks again for all your help.
Trenton

 

[Peer81]

No problem, that's why we're here!

Greetings Peter