# Transmission Swap?



## EthMills (Oct 25, 2020)

Hi, 

I have a 66 GTO with a 389 and 3 speed auto on the column. I really want to do a transmission swap but want to know if it’s really worth it. The vehicle is not numbers matching and I’m not worried about racing the vehicle. Just want to make the GTO a fun and exciting street cruiser.

If it is worth doing a trans swap. Is there any kits available or guides with parts list. I have the mechanical knowledge and skill to complete it myself just want to make sure it’s worth it.


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## pontrc (Mar 18, 2020)

Welcome, if you do a lot of interstate cruises or power tours maybe something to look into. I’m telling myself if I keep mine probably will trade the old turbo 400 for a 200 4R


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## 1968gto421 (Mar 28, 2014)

A '66 with a column shifter with 3 speeds? I knew the original was a two speed automatic as the three speed TH400 did not become available until 1967 with the 400 engines. If yours is actually the ST300 two speed a trans swap would give you a lower 1st gear for much better acceleration. In that intance a BOP TH350 is a bolt-in swap for those cars giving you much better acceleration. If indeed you already have a real three speed tranny (TH350 or TH400) you are doing well. The only improveement would be if you consider the highway rpm's too much with your current combo, then swapping to an OD automatic would be your best choice. I'm told that for your car with mostly stock engine, a 200-4R is an easy bolt in but since the trans has a Chevy bolt pattern, you will need an adapter plate between the engine and trans (see link)






JEGS 60170: Engine to Trans Adapter Plate Chevy Engine to B.O.P. Trans - JEGS High Performance


Adapts 62-Up Chevy V8 (except LT & LS Series) to 66-Up Buick, Olds & Pontiac TH350, TH400 & 700R4 transmissions.




www.jegs.com





Driveshaft length and trans yoke will be concerns as will the TV cable. See link for good tech info on this:









200-4R Tip Sheet, 200-4R Information, 200-4R Swap, 200-4R Problems, 200-4R Tips, 200-4R Specs - PATC - TransmissionCenter.net


200-4R Transmission FREE Advisory Tip Sheet, 200-4R Specs, 200-4R Information, 200-4R Swap, 200-4R Problems, 200-4R Tips




transmissioncenter.net





If you plan on engine mods to increase torque and horsepower, you are better of getting a 4L80E trans. Here's a link with much great info on doing this.






4L80E Install in a 68-72 A-Body - PY Online Forums - Bringing the Pontiac Hobby Together


4L80E Install in a 68-72 A-Body Pontiac - Street



forums.maxperformanceinc.com





Good luck with what ever you decide to do


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