# 65 GTO ST300 to 4 speed Transmission conversion question



## larsdav4 (Jul 1, 2018)

Hello GTO lovers. New to this forum, and had a question for the pros. I am currently not able to go out and peel my carpet back from my 65 to look for this myself.. so I figured I would ask. Does anybody know if the 65 GTO factory automatic trans car has a "knockout" in the transmission hump to easily convert to a 4 speed car? I am contemplating a conversion, however, I refuse to cut into the steel, or modify anything that isn't reversible. Is there also a knockout on the firewall for the clutch pedal?

Thank you very much in advanced!

Larry


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## GTOJUNIOR (Aug 7, 2011)

There were/are no knock outs. If you've' ever seen some of the factory cutouts you'd swear it was done with a can-opener.
I think if you cut a decent/clean hole it could easily be re-installed/welded.


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## larsdav4 (Jul 1, 2018)

Thanks GTOJUNIOR, I think I have made my decision to go ahead and do the conversion from the ST-300. I have a few more questions:
If I go back in with a M-21, will I need to change my driveline (length)? Also, what rear end gears would be best suited for a M-21? Would I have to install or modify the crossbeam, And finally, would anybody know if I will need to increase the height of my hump? 

Thanks a ton!

Larry


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## GTOJUNIOR (Aug 7, 2011)

Larry to do this upgrade you will need a MT tunnel avail from most major Pontiac Parts vendors.
The last '66 ST to 4spd swap we did, didn't require any mods to X member and/or drive shaft, but don't know if this will apply to '65. 

Gearing changes and or requirements I'll leave to those more knowledgeable in that.

Cheers


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## larsdav4 (Jul 1, 2018)

GTOJUNIOR, you are one hell of a guy! Thank you very much for the photos, that was a lifesaver. Say, when you cut the hole for the tranny, did you have a measurement, or did you lower the body onto the chassis and mark where the hole needed to be? I have my body at the paint shop and my chassis at my shop, so I am trying to get it figured out where the hole goes.. Also, did you use panel bonding cement to glue to hump on, or did you weld it?

I truly do thank you for your images - you have no idea how much that helps me. Thanks for being a support to the GTO community!


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## PontiacJim (Dec 29, 2012)

I don't know how far off or if even the same, but here is what I measured on my '68. https://www.gtoforum.com/f146/correct-transmission-hole-floor-118961/

The shifter hole, as already mentioned, is not very clean at all. Try doing a search using the google search of the forums and you may find the answer.


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## GTOJUNIOR (Aug 7, 2011)

Sorry didn't record any measurements, it was a fit and and fit again to be sure we had the clearance needed.
Setting the trans without the stick will also give you a good point to start.

As I mentioned earlier the factory installations were far from precise and/or clean. 

If you had the tunnel in hand you will note the contours/shape will almost exactly dictate the placement.
Also take note of the AT shifter hole in the images below and you get an idea of tunnel placement as well.

Hope these help.

Cheers.


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## geeteeohguy (Feb 2, 2008)

What Junior said. The 'doghouse' will only fit perfectly in one place on the tunnel. Mark the area with a sharpie, remove the doghouse, and cut the hole with a cut-off wheel about 1/2" inside the hole (you need a lip to screw the doghouse to). Really a simple job, and one easy to get right.


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## varmit86 (Nov 7, 2009)

I have a trans and 355 posi out of early 66 if your interested


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## maverick198 (Mar 3, 2019)

LarsDav4 curious if you installed a factory 4 speed console in your car and if you used a Hurst Competition plus shifter? Struggling with working out a shift boot/trim ring combo to work with this shifter in a factory console.


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