Scored a holy grail

Today I grabbed a driven VSS gear that looked dark blue, and when I got home, I counted the teeth...43. These are not available anywhere!!! It is the purple gear. I found it on a 93 FW with a GU2 rear. I was looking for this gear for about 2 years. I finally swapped the drive gear, and put a smaller VSS and 36 tooth driven gear on the car. This gear makes the 3.23 ratio with an 18 tooth drive gear in the trans have a correct speedo with 27 inch tires. I will continue to check the 700R4s for more gear options.

Cross posted on ISSF

Congrats on the find! They are that rare huh, yikes.

This place claims to have them for $11: http://www.transmissioncenter.org/GM_Speedometer_Gears.htm

They have some nifty charts there too.

Try buying one. They do not have them. I already tried them 2 years ago, and they did not have them then either. You can not order one.

I love finding a needle in a haystack! Nice!

Fred Kiehl wrote:

Try buying one. They do not have them. I already tried them 2 years ago, and they did not have them then either. You can not order one.

I wondered about that -- that's why I said "claim to have". All too many internet retailers just drop-ship and rely on old listings from suppliers. I've run into that myself on several occasions.

Oh well, at least you have one now!

I checked the whole United States, and found 2 places who listed one on hand. I called both, and neither had it in stock. As far as I know I have the only one not in a car in the entire US.

Fred Kiehl wrote:

As far as I know I have the only one not in a car in the entire US.

You better insure it!

It is hid away with my maze of hoarded parts that no one can decipher except for me. Furthermore, no one has seen one, and therefore they would not know what it looks like.

I saw a picture on that website!   

It looks like a multi-start worm. I wonder if I could make one on my lathe if necessary?

The gear is not the multi start worm. It is the driven gear with the small hole with a flat to keep it from spinning on the shaft. The purple is more like a midnight blue.

That one might actually be easier. I've made a lot of spur gears, that one is similar but with the teeth angled. Looks like the teeth are straight, not curved? Once the diametrical pitch was calculated and a suitable cutter obtained, I think that could be done on a mill with a rotary table set to the correct angle. That D-shaped hole would best be broached, but if one only needed one or two gears it could be milled.

They are straight angled teeth. The gear is the same size as the other 40+ tooth gears, but has a different tooth count. I do not know how they varied the teeth for the different tooth counts. Maybe they changed the angle and profile to keep lash to a minimum. It might be easier to make a two piece silicone mold, and cast them in epoxy, or polyester resin.

I also located the cast in tooth count on the concaved side around the perimeter of the gear. It is very small, shallow, and partially in the ends of the teeth.

If they are based on the same system as spur gears, the profile changes by the tooth count, but the profiles are grouped into 8 standards from 12 tooth to rack (infinite). So a set of 8 cutters is required to cover the entire range for each pitch. A #3 cutter covers from 35 -54 teeth, a #4 covers 26 - 34. I don't know what those are made of, probably some sort of cast plastic all right. I was thinking they could be cut from Delrin round stock or possibly even aluminium.

They are injection molded, but I do not know what plastic they are made of. They are marked with a PG opposite the tooth count if that is any help.

PG - Powerglide.   

I managed to find another 43 tooth gear. I am willing to part with one for $25 shipped. You need the 40+ tooth VSS to use it.

Not as rare as you thought?  

That is two, and the second one is the only one available for sale in the World. The only reason I have two is that I know where to look for them. That does not mean I am going to find one every time I look. I was fortunate to find the two I did. I am sure there are more, but how often do you see them?

Not sure that this is the part you were talking about, but they seem to be quite plentiful on eBay.

Is there a difference that I am missing?

43 tooth speedometer gear

Interesting. Many only list that gear as fitting the 91 and older 700R4 / TH 400 / TH350. So while they look the same (and one photo is even purple), there may be a slight difference in dimensions (shaft diameter? Length?) Other listings suggest the 700R4 and 4L60 gears are interchangeable -- and it was always my understanding that only the nomenclature changed. Maybe the gear is seemingly rare and not listed for the later vehicles just because GM discontinued it at the time they changed the 700R4 designation to 4L60?