TAC Tech => Mechanical => Topic started by: kev 190164 on March 16, 2025, 10:38:46 AM
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hello can someone tell me which flywheel i need to put on my 1974 455 trans am . converting to manual and using a t56 magnum . is the engine internally or externally balanced
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For what I've researched on the fly in response to this question, a lot of people are just using a stock-style flywheel.
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I don't have an answer for you. Likely someone who sells Tremec upgrade kits could answer your question. A quick search turned up Modern Driveline. There are likely lots of options.
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As assembled from the factory they are balanced externally at the flywheel. However, they are not so far off as to require a severely off balance harmonic damper like a chevy small block 400. When I had my '70 455 built I had the option to select internal balance, requiring a neutral balanced flywheel. A factory flywheel was neutral balanced, but I am not sure I would use a factory cast iron flywheel and aluminum bell housing again for safety reasons.
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With my t56 swap. I used a Pontiac flywheel and clutch kit. My rotating assembly was internally balanced when i had it built, so I'm using a neutral balance flywheel. When you pull your trans out; you can look at the flywheel or flex plate to see if you need a neutral balance or external balance for your engine. Here's a link that has info on how to tell the difference.
https://butlerperformance.com/n-13498-internal-neutral-vs-external-stock-balance.html
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the 455 is all standard just want to fit the t56 . its an auto at the moment just want to know for sure if external or internal balanced . i have a duel clutch and a steel bellhousing
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If your rotating assembly has never been out of the block and still at factory specs. It'll be external.
If the rotating assembly has been out of the block and not balanced; it's external.
If the rotating assembly had been out of the block and balanced; it's internal.
If you're not sure if it has been balanced or not; you will need to look at the flexplate. The link i sent in my last message will help identify what you have.
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the 455 is all standard just want to fit the t56 . its an auto at the moment just want to know for sure if external or internal balanced . i have a duel clutch and a steel bellhousing
You will more than likely need to align the bell housing to some tight tolerance. I used these bellhousing alignment dowls (attached link) when I did my TKX 5 speed swap with warmed over 400 pontiac. I searched high and low for good dowls and couldn't find any better.
You can use a brass bushing for older GM manual trans but the newer made by Tremec trans like yours and the TKX, TKO ect should use a pilot bearing. The reason is the trans has a front tapered bearing. That tapered bearing can be ruined and cause other problems if the input shaft is not centered properly by using offset dowls as needed after you measure the off-center run out of the bell housing to center-line of the crank. Silver Sport Transmission has some good videos on how measuring that run-out.
There's lots of little things to watch out for when doing this swap, good luck.
https://www.robbmcperformance.com/products/dowels.html
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Wow, that swap has been in the back of my mind for some time now. Great info. Thanks everyone.