Drive gear for speedometer

Reply Subscribe

Thread Tools

Search this Thread

Sep 12, 2006 | 07:15 AM

7T2Z28

Thread Starter

Intermediate

Joined: Sep 2006

Posts: 26

Likes: 0

From: Madison Heights MI

Drive gear for speedometer

Anyone know how many teeth are on the drive gear in the 4 speed manual transmissions for 1977?

Sep 12, 2006 | 07:24 AM

Tonys96

Drifting

Joined: Jul 2002

Posts: 1,943

Likes: 1

From: Rosemount MN

The drive gear, on the output shaft is 7 or 8 teeth.

Sep 12, 2006 | 07:32 AM

7T2Z28

Thread Starter

Intermediate

Joined: Sep 2006

Posts: 26

Likes: 0

From: Madison Heights MI

Yup, it's 7. I need a 19 tooth driven gear as I suspected.

Thanks Tony.

Sep 12, 2006 | 08:36 AM

...Roger...

Race Director

Joined: May 2006

Posts: 16,528

Likes: 53

From: Dayton, Ohio

Quote:

Originally Posted by 7T2Z28

Yup, it's 7. I need a 19 tooth driven gear as I suspected.

Thanks Tony.

Did you read in a book it is 7 or did you look at it and see the color?Just curious.

Sep 12, 2006 | 08:50 AM

7T2Z28

Thread Starter

Intermediate

Joined: Sep 2006

Posts: 26

Likes: 0

From: Madison Heights MI

I guessed.

I can't really see the drive gear without taking it all apart. I do have a 3.70 rear end and I know the tire size. With a number 21 driven gear it's off about 10 mph low. I was going to go to a 19 anyway, but I wanted to confirm that with the formula.

Just out of curiousity on my part, do you have the color code/tooth count on a chart or something? I've been unable to find that info. There seems to be a lack of speedo drive gear info, driven gear stuff however is abundant.

Sep 12, 2006 | 10:00 AM

...Roger...

Race Director

Joined: May 2006

Posts: 16,528

Likes: 53

From: Dayton, Ohio

Quote:

Originally Posted by 7T2Z28

I have a GM parts manual dated 12-1983.It shows 7,8 and 9 teeth.I've used this book since 1984 and I'm pretty good at it but these gears are confusing.I look inside at the color for a place to start rather than trying to guess.In your year there were many variables.75-79 Best way is what your doing -just change agear and go from there.If you dont want to buy gears go by a trans. shop and swap with them.They usually have a box of old ones.You could leave a deposit and take several and try them and take back what you dont use.

ps-my box has about 15 in it.