I have a 383 stroker that vibrates when driving. When you push the clutch in the vibration goes away. When I drove it again, the starter gear came off the flywheel after I let the clutch out. What could have caused this?
Gotta be something catastrophic like that. I'd go over the flywheel looking for cracks going out from the mounting holes to start off. I'd put a new flywheel on it indicate it to rule out a bent crank flange. Bob
If that used a 400 crank, you have to use a 400 flywheel. It is externally balanced. The hormonics set up by not using one can cause the ringear to slowly walk off the flywheel, bolts to loosen, brackets crack, etc. It also requires a 400 balancer.
If the vibration goes away when you push in the clutch I'd think that the cause of the vibration is either in the clutch disk or behind it. NO or wrong pilot bushing would be one thing to look at. You didn't say what trans but a lot of the newer transmissions seem to run a metric pilot bushing rather than the standard "we've used this one for 50 years one that we are used to using. Wildethang.1732 and I were posting at the same time and that was my first thought until you said that the vibration quit when you pushed the clutch in and the vibration went away. If the flywheel was wrong one would have to think that the vibration would still be. Still that is worth considering as it may not be the correct flywheel for the crankshaft used. We ran into that in the other direction on my brother's 77 Chev pickup years ago when he had the trans done and a new "400" flywheel installed and got a big vibration. Turned out that his "400" engine that he was so proud of was a target 350 that someone had stuck in the truck. I knocked the counterweight off with a hammer and chisel and the vibration went away. Meaning, make sure all the pieces match from vibration dampener to the flywheel and through the pilot bushing and input shaft on the trans.
Pilot bushing/bearing or bad input shaft bearing. If the remedy is pushing in the clutch, the vibration is not in the engine. A bent or out of balance drive shaft would vibrate even if the clutch were disengaged, if it only vibrates while driving. Losing the ring gear could be related or could be coincidental. Aftermarket flywheel?
Possibly. I was thinking that the flywheel runout (however it happened) was the root cause of the vibration, disengaging the clutch lessened it. The wild card is the blown ring gear. The OP needs to take a real good look at the flywheel and probably everything in the food chain. Bob
snot rocket is right,if it is trans related all indications of trouble go away when clutching....that said, wildthang is right to state that a 400 is truly externally balanced and there is a difference between the flywheels both manual and automatic....this will cause a serious vibration that only gets worse as you've found and eventually lead to failure of the flywheel causing major damage to both the block and possibly the trans. This can also cause a sound that almost sounds like an off rod knock when in the early stages as the bolt's walking away from the flywheel will start to touch on the bell housing mounting flange/area of the block. Look at that area from under your car and see if there is any evidence of this....also try and roll the motor BY HAND and look at the alignment/spin on the flywheel..if it has any wobble at all being manual it has surely fractured somewhere usually at the center of load. Also this will certainly start to touch on the starter housing or shaft and eventually try and rip the starter from the engine leaving you with broken starter bolts to fish out of the block with a drill and easy out plus a chase of the threads....not fun in the cold believe me....I am speaking from experience....still have the broken starter bolts as a reminder....good luck and may the car god's smile upon you during your repair
SCAT also has a 3.750" stroke crank that is INT front and EXT rear balance. This of course as well as the INT/INT and EXT/EXT balance 383 cranks. You need to be 100% certain of which crank and damper-flywheel/flexplate you need for your specific engine.
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