I have a 68 J code that i just had the 302 completely rebuilt. After reinstalling the motor everything runs really well. However one thing I can’t seem to diagnose is the increased engine vibration. I checked the motor and tranny mounts and they are all good. I’m wondering if it might be the new flexplate I installed before putting the engine back in. I was almost positive the bolt pattern only allows you to put it back in one way though. Am I wrong on that? I would like to hear ideas or opinions on what might be causing the vibration. As always thanks for the help
first thing that jumps into my mind would be a flexplate or harmonic balancer imbalance issue… were either replaced and perhaps wrong with the whole 50 oz vs 28 oz imbalance issue?
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Well you should confirm if the vibration is from the engine alone or the drivetrain. Does if vibrate in neutral? A specific RPM? Or does if vibrant only when in gear. This will help narrow down the possible cause.
Do you have the mass damper still on the transmission? I’ve been chasing an annoying small vibration for a couple of years. Vibration comes in a 2000 rpm, even in park / neutral
Put in a rebuilt roller cam 5.0, with the correct 50oz balance damper and flex plate, had the torque converter and transmission rebuilt but still had the vibration. Only original part p/s pump, but vibration is still there with all belts removed.
Spoke to guy with 68 Mustang who had a similar problem. He said it started when he removed the mass damper from the transmission. Put the damper back on and vibration went away.
Unfortunately I haven’t been able to find a damper to test.
I replaced the existing flex plate with an OEM spec one from summit. 28oz.
Unless the one i pulled off was the updated 50oz it shouldn’t be that.
Can the flex plate be installed only one way? Meaning the weight that’s welded on is not on the correct side if installed wrong. I was pretty positive the bolt pattern only allowed for one way to bolt to back of motor.
It shakes pretty good in nuetral and throughout most RPMS. I had a mild comp cam installed but it seems to be too much shake for that to be it but 8 could be wrong.
I’ll be honest man. I’m not sure what a mass damper looks like so i couldn’t say. Where is it located exactly and what does it look like?
I didn’t have any leftover parts after the rebuild so hopefully that’s not it.
Flex plate only fits one way. Should be 157 tooth / 28 oz imbalance.
Harmonic balancer should be 3 bolt C8 AE.
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Probably won’t be a mass damper if it shakes badly. Also called TRANSMISSION VIBRATION DAMPENER - C4 on WCCC
Yeah just looked up what that was on their site and mine is still bolted up there. At least i know what that is now i guess lol.
I have a 67 Cougar XR7, 351w & it had a engine vibration that followed the rpm’s. Turns out the Centerforce clutch weights had settled in a off center position. Had to pull the t5 trans and remove them. That fixed it. Figured it out threw the internet forums. Never again a Centerforce clutch.
I have a C4 automatic so that wouldn’t have any clutch weights would it?
Hi: I sent basically the same reply to the other member that was having a vibration with the crate engine. Your best source of information is going to be from an engine balancing shop. Just google engine balancing and find one in your area. They are an encyclopedia of information on engine balancing issues.
I was unaware of that so I will definitely reach out to a local shop about possibly trying to diagnose it
Just tossing it out there but one time we had a fan blade fall off unknowingly. Engine would shake and none of us thought to count the blades on the cooling fan.
No.
Something is not balanced correctly. If you have verified that the flex plate and external balancer are the same weight, there could be something going on internal to the engine. Uneven clearances on the crank will make an engine shake itself apart. I would speak to the engine builder…