Changing tranny/speedo gears - Team Camaro Tech
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post #1 of 29 (permalink) Old Sep 26th, 07, 07:02 AM Thread Starter
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Changing tranny/speedo gears

I have searched and read many threads regarding which drive/driven gear I need to get my new tranny/rear end combo calibrated (TH350/27"tire/3.70). I think I need a 20 / 7 combination, but how do you install them? Are the behind the cable receptor on the tranny? I have not even looked at the tranny, but I now the car has the exhaust system on it and driveable, I would like to know how fast I am really going.

Thanks!

Strick
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post #2 of 29 (permalink) Old Sep 26th, 07, 07:16 AM
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Re: Changing tranny/speedo gears

You will need to pull the tail section off the tranny to get at the internal 'drive' gear teeth to change it, then the 'driven' gears do change out behind the speedo cable connection.

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post #3 of 29 (permalink) Old Sep 26th, 07, 07:42 AM
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Re: Changing tranny/speedo gears

Quote:
Originally Posted by click View Post
You will need to pull the tail section off the tranny to get at the internal 'drive' gear teeth to change it, then the 'driven' gears do change out behind the speedo cable connection.
How much of a job is that? I want to do this also, but not until I change my rear end gears w/posi. Can the tranny still be installed in the vehicle to do this?

Last edited by tgifford5; Sep 26th, 07 at 07:43 AM. Reason: additional question
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post #4 of 29 (permalink) Old Sep 26th, 07, 07:45 AM Thread Starter
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Re: Changing tranny/speedo gears

Click - what are the chances of just being able to change out the 'driven' gear, and not the drive. I just finished my car and got the X-pipe exhaust put on yesterday. I am not in a current state of mind to drop everything and pull off the tailshaft.

Thanks

Strick
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post #5 of 29 (permalink) Old Sep 26th, 07, 07:50 AM
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Re: Changing tranny/speedo gears

Strick and Ted, read this page thoroughly http://novaresource.org/speedo.htm. then compute your value and count the teeth on the drive gear (take speedo bullet out of trans, look through hole to mark a tooth and count, turn driveshaft with rear wheels up and trans in neutral). Then find the closest speedo gear (driven gear) from the charts. Buy correct color and tooth count on ebay (cheaper) and R&R driven gear in speedo bullet. No need to remove trans or tailshaft, it worked great on my car!
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post #6 of 29 (permalink) Old Sep 26th, 07, 08:07 AM
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Re: Changing tranny/speedo gears

I would try to just change out the driven gear. They are all the same except the turbo 400 ones. I have 3.73s and have the yellow 24 tooth gear (GM). I would try that and see where you are. Mine is pretty close, but I haven't checked it for being spot on. If that's not right you could try the 23 tooth black.
I don't know about autos, but on Muncies there is a bolt on the side of the speedo housing with a piece of flat metal that holds the "bullet" in the tranny. This bullet slides out once the bolt and holder are removed. Be careful as the gear can fall in the tranny. It goes in from the back side of the bullet and therefore comes out the back. Before you pull it out you might try to hold the end where the speedo cable goes into the gear with a needle nose or something.

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post #7 of 29 (permalink) Old Sep 26th, 07, 08:27 AM
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Re: Changing tranny/speedo gears

As Kevin said, try the 'driven' gear change first and if that gets you close enuf to correct speed, then you can skip the 'drive' gear replacement. If you have to get into the 'drive' gear, its 4 bolts, remove driveshaft and lose a little fluid. Ive not had to remove mine, I just had the 'driven' replaced and it got me right on speed now.

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post #8 of 29 (permalink) Old Oct 16th, 07, 07:30 AM Thread Starter
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Re: Changing tranny/speedo gears

Is there a stock driven/drive gear setup that is the same in all TH350?

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post #9 of 29 (permalink) Old Dec 6th, 07, 04:47 AM
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Re: Changing tranny/speedo gears

This is great information since I am attempting to do this now with my Nova. I believe my Muncie is an M20 (stamped with a C suffix) but that doesn't seem to matter since the speedo output should be the same for all Muncies. It currently has a yellow 24 tooth driven speedo gear and the speed is way off. I tried an old blue 20 tooth gear and got nothing but a bouncy needle. The blue gear was smaller in diameter than the yellow and I was ignorant to the fact that they do not interchange.
I'll use the Novaresource guide to get me on the right path.

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post #10 of 29 (permalink) Old Dec 10th, 07, 02:53 PM
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Re: Changing tranny/speedo gears

I made a mistake on my prior post. My trans suffix is A, not C.
I removed the speedo bullet and driven gear. Counted the number of teeth on the drive gear and it appears to be 7 (it is yellow). My calculations put me at 2.67 ((3.55 X 20.2) / 26.85), but going by the chart at Novaresource, there isn't a match for me. My driven gear is about 7/8 in diameter instead of 3/4 or 1-1/2. What the heck do I have?

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post #11 of 29 (permalink) Old Jul 28th, 09, 08:07 PM Thread Starter
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Re: Changing tranny/speedo gears

A thread back from the dead. I think almost 2 years is enough procrastinating.

To remove the driven gear, is it as simple as removing the 3/8" head bolt that secures the keeper and pull it out? Tranny = TH350

I am hoping it is as simple as that and a 6 mile trip to Summit for a 22 tooth grey TCI driven gear to replace what looks white to me from the outside of the tranny.

Thanks guys!

Strick
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post #12 of 29 (permalink) Old Jul 29th, 09, 06:59 AM
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Re: Changing tranny/speedo gears

Does the tranny fluid need drained to change out the speedo gear on a TH350?

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post #13 of 29 (permalink) Old Jul 29th, 09, 07:54 AM
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Re: Changing tranny/speedo gears

Quote:
Originally Posted by Strick View Post
A thread back from the dead. I think almost 2 years is enough procrastinating.

To remove the driven gear, is it as simple as removing the 3/8" head bolt that secures the keeper and pull it out? Tranny = TH350

I am hoping it is as simple as that and a 6 mile trip to Summit for a 22 tooth grey TCI driven gear to replace what looks white to me from the outside of the tranny.

Thanks guys!
Yes! It's that simple.
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post #14 of 29 (permalink) Old Jul 29th, 09, 08:46 AM
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Re: Changing tranny/speedo gears

Nope fluid is below that level, might get a dribble but no need to change or drain it.

Click..is Jim..former owner of a 69RS-LM1 350/255 - 700r
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post #15 of 29 (permalink) Old Jul 29th, 09, 08:53 AM
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Re: Changing tranny/speedo gears

There were 4 speedo drive gears (7, 8, 9 , 10) for a TH350; orange, white, black, purple.

What color is yours? Just remove the speedo bullet to see your drive gear for the color.

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