Speedo Gear Question TH350

[d_hache]

Hello, i am in the process of restoring my 1980 Trans Am.
There transmision was leaking by the speedo gear housing.
I beleive the transmision is a TH350 that came off a 1981 Pace Car.
The gear has 45 teath on it.  I found the part on Classic Industries but it says it does not fit a 1980 or a 1981 Trans Am.
Is it possble someone installed the wrong gear way back?
Let me know
Thanks

[SoupMan]

The TH350 has two different speedo housings. If the car is equipped with the original factory transmission then the site should be pointing you to the correct gear.

For those trying to figure out what housing they have
https://www.theamalfiexperience.com/profileo/index.php?keyword=and-housing-set-Replacement-Parts-109822

In you case it could just be the supplier website omitted some part numbers because they didn't see it as part of the original factory offering OR someone changed the rear gear ratio hence adjusted what the speedo gear was.

Either way, you need to know what rear gear you have to know what speedo gear you will need. Do you know if the speed was accurate before the gear went?

[SoupMan]

This to solve the leak:
https://www.summitracing.com/parts/tci-880023

To replace the gear:
https://www.summitracing.com/parts/tci-880032

If your gear is worn, you may need to replace the other gear inside. Not sure the name but looks like this:
https://www.summitracing.com/parts/tci-880015

[5th T/A]

I believe this is the type of housing you should have. It's the only one I have seen on Firebirds, but you should double check yours.

Unless the driven gear is damaged/cracked it does not need to be replaced. There are two places it could leak, the large O-ring that goes around the housing Shown in number 1. More likely it is the seal the shaft of the driven gear rides in, shown in number 3, left hand holding the seal. Unless something is damaged you should only need these two seals. But I am not sure where you can purchase just the seals, I will try and research.

Images are from Cliff Ruggles Turbo 350 Transmission book. Cliff sells carb parts, not sure if he sells these transmission parts.


Document_2022-02-03_135340 by Lawrence Alexander, on Flickr

[5th T/A]

I would like to add that if the transmission is not original to the car or someone replaced the rear end or changed the axel ratio the driven gear may be incorrect and may provide an erroneous speedometer reading.

Here is a link to just want to purchase the housing O-ring, inner lip seal with clip.

https://www.classictransmissionsolutions.com/th350-speedo-gear-large-housing-leak-stop-kit-turbo-350-speedometer-oring/?msclkid=6b9fbc8799f818a5f93ddd7bd85954ff&utm_source=bing&utm_medium=cpc&utm_campaign=**LP%20Shop%20-%20Speedo%20Parts%20%26%20Calibration&utm_term=4585788121634428&utm_content=264%20%7C%20TH350%20Speedo%20Gear%20Housing%20LEAK%20STOP%20KIT%20Turbo%20350%20Speedometer%20Oring%20%7C%20%2414.28

[Wallington]

Don't confuse Chev TH-350 and BOP TH-350, completely different units and speedo gear setup. Of course, later years with chev engines may be exactly what you need, just have to know first. Others have mentioned this above, but not why they are different.

If you took a 44-tooth gear out of it then it's a BOP version with 40-45 tooth driven gear. Also know that BOP TH-350 use the same speedo gears as the TH-700. Many auto shops will automatically list the TH-350 gears as the Chev version, and the TH-700 gears, no mention at all of the BOP TH-350. As usual, do your checks first. They also look very different so the look and the numbers can't be confused with either box.

If you can see the colour of the inner gear then you can also work out the ratio, assuming you know your rear axle ratio and tyre diameter, if you question your calibration.

https://transmissioncenter.net/product-tag/speedometer-gears/?product-category=th-350