What color is this speedo driven gear? White or Yellow? What color do I need?

I replaced the Speedometer housing o-ring tonight - the old one was hard and flat.
After the new one was on, it fit snugly back into the bore.

I know the rear end has been upgraded to 3.42 Posi
Given the tires are 255/60-15's which are 26" tall

I guess my question is, how many teeth are on that color drive gear?

 

You mean the drive gear. Count 'em! Hint: mark a tooth with a black marker so you know where you started...

Devon

 

Well Dang! Its all back together now! LOL
I didnt think Id be able to turn the 'drive' gear to count them (I assume you'd have to count the teeth on the end looking at it like a clock)

 

Bummer - the counting is easy with the rear tires off the ground!

For what it's worth, the drive gear appears to be "natural", the term used when color was not added to the plastic resin. Don't know if that helps or not. The plastic turns to a darker color thanks to age, heat and the red dye in the transmission fluid.

Devon

 

Yip
If it leaks again, I'll remove it and count...
but Murphy's law dictates that I'll no longer get a drip from here ou:

 

Found this on an Oldsmobile site...
All the Natural gears have 19 teeth

 

This site too, says 19 teeth for natural color...
Now to find a calculator to figure out the speedo gear!

http://www.chevymania.com/tech/speedo.htm

 

255/60-15's which are 27" tall.
The rear is 3.42
Drive gear is 19 teeth (according to the references above)

according to this site...
http://tri-5.chevyrides.com/speedo.php

I need a 48 tooth driven gear, I dont think they make one, or at least a quick google search does not yield any results... bummer

 

Yep, might have to change the drive gear unless someone else has a better suggestion.

Devon

 

The only column you are concerned with is the far right TurboHydro. The gears you are referencing are the smaller Chevy manual/t350 driven gears. I checked a gear I have and it is the same color you have and it is 18 teeth just like the top of the column states so you can reference off that column. The adapter column is for a speed reduction unit that you have to screw onto the speedo cable housing when you use steeper gears or shorter than a certain tire. Go with the 45T driven gear and you'll be ok.

I like that calculator you found because it takes into account loaded diameter or rollout which is always shorter than what you measure freestanding.

How many teeth is you driven gear now? Just checking because you need the 40T and up carrier. I believe it will say so on the back of that plastic carrier. If it came with a 40T+ gear you'll be ok. The numer is imbeded into the gear on the shaft side up near the teeth or sometimes right in the middle of the opposite face.

 

You have pretty much the same set-up as me. Stock gear for this application is the green gear.

 

Green gear has 42 teeth.

 

confusion has set in :laugh:

The calculator says I need a 48 tooth.

Mike says a 45 tooth will work.

Dave says a 42 tooth will work.

Im assuming that I'll need the new 40t+ housing so I'll keep an eye out at the junk yard

 

Curtis, what trans do you have? I gave info for turbo 400. If you have 4 spd I may have given you wrong info. Up until last year some of the sleeves were still available new from GM for about $25. I can check numbers later and see if still available.

 

Its a TH400

 

What gear you have now will tell you if you need a housing. If it is already in the 40's then you can use your housing. If you look in the box that concerns 3.42 gears the difference in driven gear teeth has to do with tire height. The taller the tire/higher the rear gear the faster the speedo needs to be driven and the less teeth you need. The shorter the tire/the steeper the rear gear the more teeth the driven gear needs to slow down the speedo. That site you referenced shows that perfectly.

Notice on the sheet how the taller the tire the greater the number the driven gear teeth are.

 

National Parts Depot has a green 45 tooth for $6.95
Cant find a 42 tooth on their site.

 

3.42 axle will put you out of range of a 19 tooth drive gear. 18 is
still marginal. I have seen all the way down to 15 tooth, one of
those should solve your problem. Bruce Roe

 

NPD must be a mistake unless their 45 tooth is light green.....Here is some more info. In 71 the correct gear for your combo is 42 green. In 70 a 3.42 gear car with turbo 400 and BB coded trans is also 42 Green. If you have 3.42 with BS coded trans in 1970 you need 44 tooth gray gear. Not sure why different coded trans is different but this is closer to your 44 calculation. Also the sleeve for the higher tooth gears is GM #1362293 and it is still availbale from GM. Try your local dealer or try GM parts direct. Cost from them is $29.83 but they kill you with $12.95 shipping. I ordered one because why not why it is still available. Thing of the savings not having to drive around not looking for one.:Smarty: By the way all my info is based on Buick speedo charts assuming car is using G60-15 inch wheels which are about 26 to 26.5" tall.

 

I beieve turbo 400 in 70 should have a 18 tooth drive gear.