I checked this link http://novaresource.org/speedo.htm to find which speedo gears to use on my rebuilt M20 and I'm not sure I'm counting the drive (trans) gear teeth correctly. The steel gear on my output shaft looks like 5 or 6 teeth when I count across the teeth. The chart shows the smallest trans gear as 7 teeth. Does anyone know what I'm doing wrong? Wally?
Thanks,
Rich

you need to count the teeth from there starting point on the side of the gear

How about this:
vvvvv
l l
l l I counted 5 or 6 teeth (indicated by the v's) depending on how the gear l l is turned. Correct?
l l
l l
vvvvv

Thanks,
Rich

That didn't turn out as I intended it to, but hopefully, you get the idea.
Thanks,
Rich

How about this:
vvvvv
l l
l l I counted 5 or 6 teeth (indicated by the v's) depending on how the gear l l is turned. Correct?
l l
l l
vvvvv

Thanks,
Rich

Place the speedo drive gear flat like this (O) to count where each tooth starts. There is a 6, 7, and 8 steel tooth drive gear.

Thanks Jody, I shoul've asked this question before I reassembled. Maybe I can still count through the speedo gear hole if I can mark the end of one tooth.
Thanks,
Rich

OK, I was able to look through the speedo gear hole, marked one tooth on the trans gear and slowly turned the input shaft (trans not in car yet) to find that my trans gear has 7 teeth (I thought it was all one spiral tooth like a bolt). I went back to the site to determine that with a 3.31 rear end and 26" diam. tires, I need to get an 18 tooth speedo gear.
Thanks again,
Rich

Rich,

It is great to see a follow up post. Job well done.

OK, I was able to look through the speedo gear hole, marked one tooth on the trans gear and slowly turned the input shaft (trans not in car yet) to find that my trans gear has 7 teeth (I thought it was all one spiral tooth like a bolt). I went back to the site to determine that with a 3.31 rear end and 26" diam. tires, I need to get an 18 tooth speedo gear.
Thanks again,
Rich

I hate to tell you this, but GM never made a 7 tooth circle gear for a Muncie. They made a 6 and 8, 7 is only available in the after market world.

6 is a 4.10 only circle gear and uses a steel driven gear.

3:31 with approx 25.5"-26" tires gets a large 8 tooth driver gear and small 20 or 21 driven gear.

Scott

I hate to tell you this, but GM never made a 7 tooth circle gear for a Muncie. They made a 6 and 8, 7 is only available in the after market world.

6 is a 4.10 oly circle gear and uses a steel driven gear.

Wally, do you know who manufactured the 7 tooth drive gear before George? I have run across the 7 tooth drive gear during rebuilds years ago.

I am looking for a speedo gear company to manufacture some 6 tooth steel 1.84" drive gears. I asked George months ago but, he is still tied up with the new Syracuse 5 speed.

I thought the 6 drive (steel) and 21 driven (steel) were for the factory 4.88:1 differentials. I have these original 6/21 gears but, I never had the pleasure of meeting a customer with 4.88s for the street!

Thanks

Wally, do you know who manufactured the 7 tooth drive gear before George? I have run across the 7 tooth drive gear during rebuilds years ago.

I am looking for a speedo gear company to manufacture some 6 tooth steel 1.84" drive gears. I asked George months ago but, he is still tied up with the new Syracuse 5 speed.

I thought the 6 drive (steel) and 21 driven (steel) were for the factory 4.88:1 differentials. I have these original 6/21 gears but, I never had the pleasure of meeting a customer with 4.88s for the street!

Thanks

A starter gear for a narly small block:yes::yes: I ran them in my 55 chevy, 4.56 in the 65 SS chevelle with a 427. Back in the day a gear made the difference on the street:beers:

I've never seen a 7 tooth before George made them and only a handful of the 6s. It would be nice if he made one, might get some action with OD trannies.

All right, I'm really confused now!
Rich

All right, I'm really confused now!
Rich

Not to worry, you can get where you want to be with what you have:yes::yes:

Thanks Wally!
Rich

I hate to tell you this, but GM never made a 7 tooth circle gear for a Muncie. They made a 6 and 8, 7 is only available in the after market world.

6 is a 4.10 only circle gear and uses a steel driven gear.

Just a FWIW on this topic:

From 1969 and 1974 GM parts manuals:

Speedo drive gear, 7 teeth, 1-3/4" dia 64-69 All, Gp 4.343, p/n 3708144
Speedo drive gear, 8 teeth, 1-3/4" dia for 27 spline mainshaft 64-69 All, Gp 4.343, p/n 3708145
Speedo drive gear, 6 teeth, 1-59-64" dia. 64-69 All, Gp 4.343, p/n 3845079
Speedo drive gear, 9 teeth, 1-27/32" dia 64-69 All, Gp 4.343, p/n 3905494
Speedo drive gear, 7 teeth, 64-69 All, Gp 4.343, p/n 3924097
Speedo drive gear, 8 teeth, 64-69 All, Gp 4.343, p/n 3924098
Speedo drive gear, 8 teeth, 1.84"O.D. for 32 spline mainshaft 71-74 All, Gp 4.343, p/n 3978758

Just a FWIW on this topic:

From 1969 and 1974 GM parts manuals:

Speedo drive gear, 7 teeth, 1-3/4" dia 64-69 All, Gp 4.343, p/n 3708144
Speedo drive gear, 8 teeth, 1-3/4" dia for 27 spline mainshaft 64-69 All, Gp 4.343, p/n 3708145
Speedo drive gear, 6 teeth, 1-59-64" dia. 64-69 All, Gp 4.343, p/n 3845079
Speedo drive gear, 9 teeth, 1-27/32" dia 64-69 All, Gp 4.343, p/n 3905494
Speedo drive gear, 7 teeth, 64-69 All, Gp 4.343, p/n 3924097
Speedo drive gear, 8 teeth, 64-69 All, Gp 4.343, p/n 3924098
Speedo drive gear, 8 teeth, 1.84"O.D. for 32 spline mainshaft 71-74 All, Gp 4.343, p/n 3978758

Nice list of numbers, I think some of these just might be for the muncie
truck trans, GM does stuff like that to see if you are paying attention:yes:

I talked to George at Auto Gear just to confirm what I said earlier, 7 tooth gears are super rare, I've never seen a single one, and George has seen only one. It would be eaiser to locate a 6 tooth piece.

The reality is there is 8 tooth units all over the place, 7 tooth units available new from Auto Gear as well as 8 tooth.

The 6 tooth was made for the 4.56 and 4.86 gears, not much of that going on out here.:beers::beers:

The 6 tooth was made for the 4.56 and 4.86 gears, not much of that going on out here.:beers::beers:

Wally, put some pressure on George to do a 6 tooth 1.840 drive gear! I do everytime I talk to him! : )

If 7 tooth Muncie speedo drive gears were never made by GM for the Muncie 4-speed, how did I end up with over 50 of these on the shelf???

I will tell you how... Pontiac used them from 1966 thru the 1970 model year...
Pontiac part #9785023 is 7 teeth speedometer drive gear...

The original owner of a 1969 GTO Judge brought his Muncie in to have it rebuilt...
M-20 P9D16A still had the part number tag as I was the first open this trans since new...
Tag #9798972 after dis-assembly there it was a 7 tooth speedo drive gear...

I do a lot of rebuilds for some restoration shop in my area, so I get to see a lot of virgin Muncie's that have never been apart before... When they come in I record all the information about the trans,,, casting numbers,,, build dates,,, VIN and location,,, head marking of the bolts,,, part number tags,,, ratio,,, and speedo drive gear...

I realize that this is not from a Chevelle or a Chevrolet,,, but Pontiac is a part of GM...
Hope this helps... Crash

Just a FWIW on this topic:

From 1969 and 1974 GM parts manuals:

Speedo drive gear, 7 teeth, 1-3/4" dia 64-69 All, Gp 4.343, p/n 3708144
Speedo drive gear, 8 teeth, 1-3/4" dia for 27 spline mainshaft 64-69 All, Gp 4.343, p/n 3708145
Speedo drive gear, 6 teeth, 1-59-64" dia. 64-69 All, Gp 4.343, p/n 3845079
Speedo drive gear, 9 teeth, 1-27/32" dia 64-69 All, Gp 4.343, p/n 3905494
Speedo drive gear, 7 teeth, 64-69 All, Gp 4.343, p/n 3924097
Speedo drive gear, 8 teeth, 64-69 All, Gp 4.343, p/n 3924098
Speedo drive gear, 8 teeth, 1.84"O.D. for 32 spline mainshaft 71-74 All, Gp 4.343, p/n 3978758

I should qualify this by saying "from 1969 and 1974 Chevrolet Passenger Car parts manuals."