Internal or external balance?
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Senior User
Joined: Oct 2010
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From: Lawton, OK
Internal or external balance?
I'm fixing to swap a ZF into my F-250, and the tranny came out of a '90 F-250. I assume I'm going to have to change the flywheel because the tooth count is different (using the '90 flywheel). I'm running into trouble with differentiating the difference with the flywheel for the '76 4.9, and the '90 4.9. Are they balanced different? Can I neutral balance the flywheel and be OK, or do I even need to? From what I can tell, the 80-up 4.9's are internally balanced, but I can't find anything on the 79-older 4.9's being internally or externally balanced.
Moderator
Joined: Dec 2007
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From: Boise, Idaho
Yup, it's just the nature of the design. They're all internally balanced.
Also, just to double check, your ZF is for a small block, correct? (300, 302, 351). The big block / diesel won't work.
Also, just to double check, your ZF is for a small block, correct? (300, 302, 351). The big block / diesel won't work.
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Senior User
Joined: Oct 2010
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From: Lawton, OK
Yeah it's for a small block. Thanks guys.
Post Fiend
Joined: Dec 2007
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From: Lost
If the 90 flywheel was from a 4.9/ZF combo, you might be better off using it, the factory clutch, and starter from the 90.
I'm not sure if the later ZF clutch/pressure plate would fit the early flywheel, without issues.
Plus, if you stick with the later flywheel, the clutch parts could be easily located by simply pretending the truck was a 90 when shopping.
Of course, the tooth count variation pretty much requires the later starter, and it's associated wiring changes.
One thing that also needs to be looked at. Pilot bushing/bearing *may* be different ID for the ZF compared to earlier trans types. It would really suck to discover the input shaft won't go in, after the rest of the clutch has been bolted on and you spend a few hours wrestling the trans around, just to go back and have to redo everything.
I'm not sure if the later ZF clutch/pressure plate would fit the early flywheel, without issues.
Plus, if you stick with the later flywheel, the clutch parts could be easily located by simply pretending the truck was a 90 when shopping.
Of course, the tooth count variation pretty much requires the later starter, and it's associated wiring changes.
One thing that also needs to be looked at. Pilot bushing/bearing *may* be different ID for the ZF compared to earlier trans types. It would really suck to discover the input shaft won't go in, after the rest of the clutch has been bolted on and you spend a few hours wrestling the trans around, just to go back and have to redo everything.
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