All- while addressing the leak issues i'd mentioned in a previous post (which I'm not savvy enough to locate), we (well, my brother the mechanic) decided we should replace the speedo gear while we had it open.
The trans currently has a 38T gear, but I have no clue as to it's accuracy, especially since I recently replaced the tires. I'm not overly concerned about the accuracy, but if I can put the right one in while it's open I'd like to. Trans is not original to the car if that matters.
On another note- where do you go for your trans parts such as the aforementioned gear, governor cover gasket, and 90 degree modulator hose?
I'll be putting a new plastic trans cover on while I'm at it..
74 Cutlass Salon 455, TH400, 225 75R15 tires.
Thx in advance..

 

Before you can calculate a speedo driven gear, besides your tirre OD, you need to also know your rear axle ratio and speedo drive gear tooth count.

Google can find a calculator online, here's one.

 

Thanks..figured i missed something..afaik the car came with standard non slip differential and axle. I'll see if i can figure it out..