# 66 GTO flywheel question



## GTOmanjohn (Apr 29, 2014)

Hello everyone, I picked up a 66 GTO 389 tri power a few months ago. The car is a project and was taken apart back in 1993. Looks like the only parts missing are the flywheel and the Muncie. Can anyone tell me more about the flywheel, such as part numbers, size, etc. I spoke to one person recently and he mentioned the flywheel would be a stepper flywheel? Or it has a step on the outer two inches? He said to make sure when I have it turned that the shop knows they have to turn both sections, the higher and lower areas. Is this true? I had flywheels turned for other cars and they were smooth all the way across. Any info is appreciated.

Thanks,
John


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## ALKYGTO (Mar 29, 2010)

John, honestly I would look for a new flywheel, preferably steel, over an original that may be warped, cracked or turned who knows how many times. I would source it from whoever you get your clutch from.:wink2:


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## eeyore (Oct 23, 2014)

Some of the modern and import stuff has stepped flywheels. But if i recall correctly, these old dinosaurs will have a flat flywheel. 

The flywheel takes a lot of heat, stress, and abuse. there is no minimum thickness stamped on it like brake rotors or drums. Might be best to buy a new one. Dont forget New flywheel bolts and down pins.


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## 68GTO4004Spd (Jun 19, 2008)

They are flat. You can see a picture here.

https://secure.amesperf.com/qilan/D...6HA&order_number_e=MzUxMTgzNg==
&web_access=Y


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## GTOmanjohn (Apr 29, 2014)

Thanks for the information everyone. I may just get the new one from AMES.

John


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## 68GTO4004Spd (Jun 19, 2008)

You should get the bolts too, they are high strength to withstand that awesome Pontiac torque.


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## PontiacJim (Dec 29, 2012)

Factory flywheel is cast and flat.

The after market flywheel may be the Hays steel flywheel which will work for both the 11" and 10 1/2" clutch/pressure plate as it has both patterns drilled in it. 

If it is the Hays, which is what I purchased and used on my 400CI, it is neutral balanced for use in an internally balanced rotating assembly (pistons/rods/crank). From my understanding, the factory flywheel is balanced for external balancing. 

I assume your are in the process of building your engine? If building, you will balance the assembly to include your flywheel and harmonic balancer. If your engine is together and you plan on running it as is, the externally balance flywheel may cause a vibration in your engine because the balance does not match the factory external balance. Learned this myself and always had a vibration in my 400CI and did not know why. Figured it out, so now I know why. 

If you are building an engine, then no problem. If adding the flywheel to an already built engine, then inquire with Ames on the balance.:thumbsup:


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