# 1966 GTO manual Transmission Choice



## Muranator66GTOCNVT (Oct 20, 2021)

So my 66 GTO originally came with a factory four speed. The previous owner changed it over to a turbo 400. I’m thinking of converting it back to a manual transmission. If so which 4 speed should I go with ? Or, Has anyone opted to do a five or six speed? Is that a no no and should I keep it original 66? Just wanting some ideas


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## PontiacJim (Dec 29, 2012)

Muranator66GTOCNVT said:


> So my 66 GTO originally came with a factory four speed. The previous owner changed it over to a turbo 400. I’m thinking of converting it back to a manual transmission. If so which 4 speed should I go with ? Or, Has anyone opted to do a five or six speed? Is that a no no and should I keep it original 66? Just wanting some ideas


How much money, price range, do you have to budget for the conversion?

Are you doing this yourself or will have someone else do it?

4-speeds come in different flavors and you can go used to brand new.

Conversions to 5/6 speeds are more expensive and may even require cutting the floor's transmission tunnel in some instances. To take advantage of a 5/6 speed overdrive, you may want to change the rear gearing to take advantage of them, which means $more money. Use an online speed/mph/gear ratio calculator to input the OD gear ratio, typically around .64-.68 to see what gear ratio you want to cruise on the highway at a comfortable RPM at 70MPH. If you only drive around town, you my never see the OD gear depending on the present gear ratio.

Use the "Search Community" box at the top of the page and you will find a lot more info on the 5-speed swap or adding the 4-speed.


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## GTOTIGR (May 3, 2020)

Hi,

In addition to the cost and functionality what are your intentions as it pertains to originality? If your car is largely original, sans the transmission conversion, and you intend to keep it original, then a Muncie 4 speed, most likely an M20 would retain originality. An M21 was available and largely depended on the differential gearing ordered.

As may people are choosing to go Tremek 5 speed for highway drive-ability, that’s an option but comes with the potential alterations PontiacJim stated. As a result of many transitioning to 5 speeds, there are plenty of Muncie’s available. You’d likely be able to locate one with the date code range proper for your car. 

Independent of the transmission choice, you’ll need to locate the pedal assembly. There again, original or modern equipment comes into play. 

Did the prior owner retain the frame mount for the Z-bar?

At the end of the day it’s your car, set it up for your enjoyment.


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## NOS Only (Nov 14, 2017)

Tremec Transmissions are okay as long as you don't have a lot of power or torque and are not going to be pounding on it, like drag racing. Try working one hard and they go BOOM.

I would go with a 700R4, 4L60, 4L60e, 4L80e or a Ford AOD. Yes, those are all automatics.


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## PontiacJim (Dec 29, 2012)

NOS Only said:


> Tremec Transmissions are okay as long as you don't have a lot of power or torque and are not going to be pounding on it, like drag racing. Try working one hard and they go BOOM.
> 
> I would go with a 700R4, 4L60, 4L60e, 4L80e or a Ford AOD. Yes, those are all automatics.


When I referenced the Tremek, I was referring to the TKO-500 and TKO-600 which is what most will install. Not talking about the T5 which would be a bad choice.

A Muncie M-20/M21 can break with a lot of power and TQ, that's where the M22 comes in.

Are you saying the TKO-500/600 is a weak transmission? 

TCET4616500 ft lbs TQ

TCET4618600 ft lbs TQ


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## Baaad65 (Aug 29, 2019)

And the new TKX is supposed to be even better and smaller so maybe no surgery and different shifter positions, you can get it with a 3:27 first gear for just under 3K....that will get you out of the hole 👍 wish that one was available before I bought mine because the TKO required surgery and my interior was all done.


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## Muranator66GTOCNVT (Oct 20, 2021)

PontiacJim said:


> How much money, price range, do you have to budget for the conversion?
> 
> Are you doing this yourself or will have someone else do it?
> 
> ...


It’s not money thing, bu


PontiacJim said:


> How much money, price range, do you have to budget for the conversion?
> 
> Are you doing this yourself or will have someone else do it?
> 
> ...


Thank You. For the insight. It’s not a money thing, but I do think I want it back to original. Since it only has 22,000 documented miles. Unfortunately the guy who had it before, his wife talked him into selling all the old GTO parts because they were cluttering up the garage. What a shame. So yes, I need everything to bring it back to original


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## PontiacJim (Dec 29, 2012)

Muranator66GTOCNVT said:


> It’s not money thing, bu
> 
> Thank You. For the insight. It’s not a money thing, but I do think I want it back to original. Since it only has 22,000 documented miles. Unfortunately the guy who had it before, his wife talked him into selling all the old GTO parts because they were cluttering up the garage. What a shame. So yes, I need everything to bring it back to original


The PHS documents will tell you what transmission you had, but most likely the M20 which is a wide ratio 4-speed. The M21 is the close ratio. Then go from there.

Get a Chassis/Service Manual for your year car which will have much of the info you will need.


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## nick rice (Nov 10, 2014)

A friend of mine just ordered a Tremic TKX. Not for a Pontiac but for a new gen built up hemi going in a 79 AMC Spirit if you can imagine. TKX will handle mega torque. I'd suggest an M20 or M21 if your near stock specs and should be a more friendly insta


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## Sanders Speed (Oct 23, 2020)

I put a tkx in my 69 gto, factory stick car. I drilled a a bolt hole on each side of frame transmission cross member mounts straps, to slide cross member back , notched the opening of the shifter "doghouse " that was it. Biggest problem was moving the x pipe for exhaust system and driveshaft safety loop. 3.55 gear 2000 at 70 mph.


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## kgantzer (Jun 14, 2020)

I really like my TKO-600 5-speed in my '66 GTO- makes highway drives more enjoyable; keeps RPMs close to 2100 with a 3.36 diff.


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## gtojoe68 (Jan 4, 2019)

I replaced my original M20 when the input shaft bearing going bad destroyed the case. Factory 4sp 68’ GTO WT motor. I got a Muncie clone from Auto Gear in NY. Stronger case but nearly identical to Muncie. I altered the gearing though: 1st: 2.26, 2nd: 1.6, 3rd: 1.0 4th: .08 So it’sa bastard overdrive in 4th gear. I run 3.9 gears in back with 255/60R/15 Goodrich TA tires. Would I do it again? Probably not as the throw to 3rd is farther than I’d like and at 70 on freeway I’m turning close to 2800-2900 RPM. But as a street cruiser? Bah, no worries. The selling point was I got brand new trans for $1650 out the door. Of course that was 10+years ago. It’s as close to stock style brand new as I could get. Seeing as the original case was garbage, it would never be 100% original anyway. Too bad as the motor is #’s matching. It gets out of the hole nice and quick and the shift from 1st to 2nd never fails to give me a big ol grin and snap passengers heads around. Haha


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## geeteeohguy (Feb 2, 2008)

You can install a Muncie M-20 with zero mods to the car for less than half the cost of a 5 speed conversion. I would go with a '66-up M-20, with the factory Hurst shifter and leave it at that. Great trans and shifter combo, and will look and feel right in the car. Your car, your choice.


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## RMTZ67 (Mar 12, 2011)

I have the original 3 speed Dearborne on the floor w/3:55 gearing and if I want to get up and go...see ya. On the freeway/highway not so much, but thats ok...I like to stay off the freeway.


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## geeteeohguy (Feb 2, 2008)

The 3 speed Dearborn transmission is actually stronger than the Muncie 4 speeds used in these cars. Bulletproof.


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## Droach6498 (Nov 1, 2020)

kgantzer said:


> I really like my TKO-600 5-speed in my '66 GTO- makes highway drives more enjoyable; keeps RPMs close to 2100 with a 3.36 diff.


If youdont mind me asking Im thinking of installing one in my 65 whats the cost I know the trans around $3700 but then you need a new driveshaft right & ? Did you install it?


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