# Where to drill the 1" hole for heater core replacement



## Freddy_Krugerrand (Aug 19, 2012)

I need to drill the 1" hole in the firewall to access the bolt holding the Heater core box on my 66 GTO. Does anybody have a photo of the hole they have drilled to replace their heater core? I don't want to drill more than one hole. A photo of one already done would help tremendously. Any advice on where to drill the hole would help too. Thanks!

Does anybody know where I can see the Pontiac instructions for this?


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## Goat Roper (Oct 28, 2014)

It isn't on the firewall it is on the inner fenderwell.

On my '67 there was a dimple.
If you don't see a dimple look down between the fenderwell and firewall with a flashlight and you will see the nut.
Once you drill the hole use a 1/4" drive with an extension to break it loose and a magnetic driver to remove it so you don't drop the nut.
Post if you don't see the dimple and I will take a measurement for you.


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## GTOJUNIOR (Aug 7, 2011)

FWIW
If you get a long handled ratchet wrench set you can accomplish this without cutting anything.
My 66 has AC and I was able to swap out my Heater core in under 3 hours.
The nut can be accessed somewhat blindly but accessed none the less.
The "Hole Cutting" was just a factory service short cut as it was all about time and money. 
JM2C

Cheers


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## Pinion head (Jan 3, 2015)

GTOJUNIOR said:


> FWIW
> If you get a long handled ratchet wrench set you can accomplish this without cutting anything.
> My 66 has AC and I was able to swap out my Heater core in under 3 hours.
> The nut can be accessed somewhat blindly but accessed none the less.
> ...


Jeff is dead on. Have R&R'ed half a dozen early heater cores and have never cut ahoese in the inner fender for access. '64-67 A-body's are relatively easy to access the nuts in comparison to several later 60's GM models.


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