Help! Vibration under rpms in a 69 302 .Anyone? Bueller? Bueller??

The Hopkinator

New Member
Dec 5, 2002
The wifes 69 Fastback ( I hate the sportsroof thing) , has a mild vibration under rpms up until about 5,000 . The engine is a rebuilt 302, with a mild cam. It did it before AND after the rebuild. We thought maybe the harm. balancer. Nope. The crank was balanced out. The fan is new, and spins steady. Its the original 69 302. Ive heard that some of the old 302s and 351s will do this, and only God can make it stop,even after a rebuild. Maybe if we make it an "Eleanor",,OKAY GAH IM JUST KIDDING !! :rlaugh: Anyway, anyone ever run into this kinda deal. It gives a nice back massage while around 2500 rpms, but its rather annoying overall. :shrug:
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Well, first off are you sure it's from the engine? If you ran it up to 5k, then shifted dropping the rpm back down, would it come back? How bad is it? What condition is the carb in? What is your exhaust set up? Some ideas that I have is that your carb is out of tune, causing your engine to shake (improper float levels will cause this), or that your flywheel is unbalanced; although I would figure that it would get worst and worst the higher your rpm, but you say it cuts out at 5k.

Does it do it under power or at rest? If only under power, chech your driveshaft and U-joints. This is NOT inherent to small block Fords, whoever told you that was wrong. When you say you had the crank balanced, I assume you mean crank, rods, pistons rings, bearings, balancer, etc. It's cheap insurance to have the whole thing balanced while it's apart just to avoid the situation your facing now.