Hi all,
I was just to to see if anyone had done a setup similar to mine an what they used for a speedo gear. I took the trans out yesterday and took it to the trans shop for a rebuild and figured now is the time to do the speedo.
The trans is the original th350 for a 1972 Cutlass s and it was a 2:73 open rear
I am running a 295/50/15 which is 26.6"tall and I am going to go 3:23 gears. I'd like to find out what I need for a speedo gear and do it while the tranny is out

 

http://www.tciauto.com/tc/speedometer-gear-calculator/

Heres a calculator for that. Remember this ( copypasted from TCI's site):

Buick, Oldsmobile & Pontiac transmissions use a 2.078" diameter driven gear housing. Two housings, each made from either aluminum or plastic, are available for driven gears with 34 or more teeth. One fits gears from 34 - 39 teeth and the second one fits gears from 40 - 45 teeth.

Dont ask me which one it has originally, its been a while since i hunted that information.
I just bought a set which included everything from new housing to all seals and gaskets you need to replace, it was pretty cheap and no need to hunt for missing parts after you found out you dont have something.

But back to your question, calculator says that most accurate reading comes By using Green 9-teeth drive gear, and Gray 22-tooth driven gear.

 

Thanks for the info, where did you order the kit from? I'd like to go that route

 

It was from ebay, dont remember. All i know it was one with cheapest shipping price to Finland, lol. They vary ALOT for same part between different sellers. I just made sure it had aluminium housing and not plastic.

As a side note, i actually havent even seen plastic housing, but i quess they excists since TCI mentions they are available on either aluminium or plastic.

 

Make sure you know the number of teeth of the drive gear. It SHOULD be 18 if everything is original to the car and that would mean that you need a 44 tooth driven gear.

 

Yes, the original speedo gears are currently 18/drive and a 38/driven