# Need Transmission Hell



## temptest66 (Feb 11, 2015)

About to take on a transmission swap on my 1966 Tempest custom. It has the orginal 326 and the ST300 trans. I found a heck of a deal on a BOP TH350 for $50. As far as I know they are compatible with spline count/length.. only thing is the trans I bought was missing the speedo gear/housing. Got the housing but the speedo gear is a tough one. Apparently there are multiple options and I'm not sure which one to go with. Can anyone here point me in the right direction? Please help!


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## 05GTO (Oct 6, 2004)

You will need to get the axle ratio identification code off of the rear end, the first and middle part of 66 the code was located on the rear of the right hand axle tube. Late year 66 the code was moved to the left top of the axle tube because of a stamping machine breakdown.


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## temptest66 (Feb 11, 2015)

Thanks 05GTO!

So in the late 66's they moved it to the driver's axle on top?

I have so far found the stamp on the bottom right corner of the diff in attempt to figure out the axle ratio... couldn't make sense of the numbers


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## 05GTO (Oct 6, 2004)

temptest66 said:


> Thanks 05GTO!
> 
> So in the late 66's they moved it to the driver's axle on top?


It was toward the end of the 66 production.

Here is a listing of the codes,

Pontiac Rear Ends


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## Lemans guy (Oct 14, 2014)

Transmission center.org has a large selection, summit, JEGS, NPD Ames should all have the speedo gears


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## temptest66 (Feb 11, 2015)

Just for general information.. if your car came equipped with the ST300 and you are looking for an easy swap that will give you more pick up off the line... the TH350 is a direct swap from the ST300. Overall length is different by about an 1/8th of an inch but will work with the original drive shaft without an issue. Trans mount in the same place. As well as the linkage and cooler lines. 

The swap went off without a hitch.. will update the thread when I figure out my speedo


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