# 1968 GTO Transmission Conversion



## Mach5j (Jun 7, 2021)

I have a 1968 GTO with a manual 4 speed. I am thinking about converting to an automatic with a dual gate shifter. The engine and transmission are already out of the car getting some work done on them. I also have a TH400 sitting in the garage, is this a tough conversion? Is it even worth it?


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## PontiacJim (Dec 29, 2012)

Mach5j said:


> I have a 1968 GTO with a manual 4 speed. I am thinking about converting to an automatic with a dual gate shifter. The engine and transmission are already out of the car getting some work done on them. I also have a TH400 sitting in the garage, is this a tough conversion? Is it even worth it?


Shouldn't be too difficult if you go with the TH-400. Off the top of my head, flex plate and bolts, TH-400 kickdown switch at the gas pedal, vacuum line?, I believe same crossmember which gets repositioned on the frame, not 100% sure on dirveshaft/yolk without looking it up.

Get a '68 Chassis manual and look at all the diagrams and read the info as this will answer many of your questions.

The GTO TH-400 was a little different than other models. Line pressure was increased to make faster harder shifts and it was modified so that you can hold in the gear selected on the His/Hers shifter. You can have a shift kit installed to a stock/typical TH-400 to give you this feature. You want a shift kit that provides both manual and automatic shifting control. Trans-Go is one such kit. I would have the trans rebuilt as they are not expensive to rebuild. I think a member said around $700-$800 if I am not mistaken. Now if you have big HP/TQ, then you will want to add a few heavy duty parts to replace the factory stuff that can break.


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## BLK69JUDGE (Jun 10, 2010)

much easier than going from auto to 4 speed
shorten the drive shaft add a th400 yoke
same x membber ,, the ebrake cable hook on the x member changes,,,
a tranny cooler ,,, vacuum modulator hose,,,, kickdown on the gas pedal ,,,
flex plate and bolts ,,, shift works shift cable ,,, and a couple trinkets....

I have most of the parts needed if you decide or have a need,,,
consoles,,, shifters ,,,, cable brackets,,,th400 yoke,,, flex plate ,,, crank bolts
tranny lines,,, vacuum modulator line ,,,dip stick tube n stick

scott t


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## armyadarkness (Dec 7, 2020)

Or bring the car to New Jersey, give me all of your manual parts, and I'll do the automatic conversion for you!


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## Sanders Speed (Oct 23, 2020)

The 68 GTO auto console is a one year only, in appearance. 69-72 also work.


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## armyadarkness (Dec 7, 2020)

Pontiac seemed to do a lot of one-year-only stuff. Hardly seems cost effective.


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## Mach5j (Jun 7, 2021)

PontiacJim said:


> Shouldn't be too difficult if you go with the TH-400. Off the top of my head, flex plate and bolts, TH-400 kickdown switch at the gas pedal, vacuum line?, I believe same crossmember which gets repositioned on the frame, not 100% sure on dirveshaft/yolk without looking it up.
> 
> Get a '68 Chassis manual and look at all the diagrams and read the info as this will answer many of your questions.
> 
> The GTO TH-400 was a little different than other models. Line pressure was increased to make faster harder shifts and it was modified so that you can hold in the gear selected on the His/Hers shifter. You can have a shift kit installed to a stock/typical TH-400 to give you this feature. You want a shift kit that provides both manual and automatic shifting control. Trans-Go is one such kit. I would have the trans rebuilt as they are not expensive to rebuild. I think a member said around $700-$800 if I am not mistaken. Now if you have big HP/TQ, then you will want to add a few heavy duty parts to replace the factory stuff that can break.


Thank you, great info!


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## Mach5j (Jun 7, 2021)

BLK69JUDGE said:


> much easier than going from auto to 4 speed
> shorten the drive shaft add a th400 yoke
> same x membber ,, the ebrake cable hook on the x member changes,,,
> a tranny cooler ,,, vacuum modulator hose,,,, kickdown on the gas pedal ,,,
> ...


I also have a complete 68 LeMans that had the TH400 in, the console is on the floor but of course just the regular shifter, not the dual gate. So I do have the drive shaft and all other automatic components from that car.


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## Mach5j (Jun 7, 2021)

armyadarkness said:


> Or bring the car to New Jersey, give me all of your manual parts, and I'll do the automatic conversion for you!


Wish I could do that, I'm in Washington state and would be quite a trip.


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## Mach5j (Jun 7, 2021)

Sanders Speed said:


> The 68 GTO auto console is a one year only, in appearance. 69-72 also work.


I'm wondering if the automatic console from a 68 LeMans would work with the dual gate shifter in it?


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## BLK69JUDGE (Jun 10, 2010)

Hello from Olympia

yes the 2 speed Lemans and the 3 speed gto consoles are twins in 68

Scott


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