Th400 speedo gear
 

Anyone know what gear set I would need for my th400 speedometer setup? This is for my original 69 gto th400 I just rebuilt. I have 3.73 gears in the rear with a 30" rear tire. Tried a few of the online calculators but just got frustrated with those.

Are you talking these gears? https://transmissioncenter.net/shop/...r-driven-gear/ I'm running the blue with 3.73's and a 28 inch tall tire. Cna't remember how close we are to correct speed, but I believe it's close.

need more info. Are you sure 30"?? that's pretty large. what was your original tire and gear ratio unless you know the drive gear tooth count in your Th400.

Need to know what your drive gear tooth count (and/or color) is to use the calculators.
That's the one on your output shaft that drives the driven speedometer gear.

It's definitely 30 inch tire. Actually 30.01 according to M/T website. It's a 295 65 15. I think the Tailshaft gear is orange but it's loose right now so I will get a count. There was no speedo gear in the case though someone removed it, leaked like crazy out the speedometer cable.

I have the 16 tooth tailshaft gear my housing for the gear adjusts from 36-39

Steel 16 or tan plastic 18 drive teeth are the most popular Pontiac tail drive gears. Calc away at https://www.tciauto.com/speedometer-gear-calculator

Thanks for the handy link to the calculator. I also posted this question on a race th400 and was told 15 on the tail shaft and 38 on the driven gear tooth. The calculator verified this to be accurate. I ordered a grey tail gear and a blue driven gear.