Weighted or non weighted flywheel

[allen123]

Which one is supposed to be on my truck
72 with a 84 350 and i dont know the year on my transmission
We are trying to figure out the vibration on my truck where its coming from.
We checked it and it wasnt missing teeth or cracked from what we saw

[Elephanthead]

It depends if your engine is internally or externally balanced, transmission has nothing to do with it. If it is externally balanced you may have the flywheel on different from stock. Did the flywheel come with the engine? Did you have the machine shop internally balance on a rebuild or something?

[cparman]

350's are internally balanced. 400's are externally balanced. the 350 has no weight on the flywheel, and the 400 does. check the numbers on the pad in front of the passenger side cylinder head. I think it should be a 2 or 3 letter code. you should be able to decode that here or on the net. the raised casting numbers on the block behind the left cylinder head will confirm this also. Had a car at my shop a while back with a vibration that would make you think an engine miss kind of problem. Swapped the flywheel and it was sssmmmmmoooth!

[allen123]

Its the same one that came in the truck and its been doing it since i got it so im not sure if its internally or externally
But i think i am taking to a shop and letting him look it over and drive it and see if he can figure it out

Its had a really bad vibration and we cant figure out what it is only thing left so far is the flywheel
It Starts vibrating at about 2500 rpms and stops at 4000 and it does it in neutral so its not the U-joints like everybody keeps telling me

[dwcsr]

check the compression and do a leak down test. You should also look over the valve springs. A broken or weak spring can cause a shutter like vibration at certain rpm's without a noticeable clicking of the rocker. If you have an automaytic trans you may see a small weight spot weled to the flex plate. It is to balance the flex plate not the motor. connect a vacuum gage to the mainfold and see what it does at the speeds you have vibration at.

[allen123]

its like a really big vibration enough to put a 12 in crack in the transmission case
If it would make that big of a vibration

[67'sgota4541]

Be sure to check the harmonic balancer,sometime's the bolt in the center loosen's up.Also check to see that the rubber in the balancer hasn't started to come apart.

[allen123]

I did i just replaced it thats why the only thing left is pretty much the flywheel. Somebody said bent fan blade but i tried that too and still vibrated
But thanks for your input

[67'sgota4541]

Your welcome.Hope you get it fixed.

[primered_junk]

84 350 is internal balance, the one piece seal motors are external, but those are the 87 and later variety. Take the converter bolts loose and push the converter back into the pump, start engine, don't rev too much or it will go boom, if the vibration goes away it's in the trans or further back. The one piece seal motors have a "bat sign" looking weight on the inside, and the 400 piece has a massive weight on the inside. I have chased vibrations like that for months, to find out it was the trans the pump will wear and shake one to death.

[70rs/ss]

Yeah, I was thinking the input bushing for the converter, or the pump itself. Be sure to push the converter back so it doesn't contact the flexplate while you run the rpm's up, and yeah with no converter hooked to the engine it'll wrap up fast (rev up, so light on the GO peddle!)

[WIDESIDE72]

Originally Posted by primered_junk

84 350 is internal balance, the one piece seal motors are external, but those are the 87 and later variety.

I just learned that the 87 up motors are externally balanced like an old 400. I buddy bought a Ramjet 350 crate motor and he had an external balance flywheel Jeg's recommended. I called them to be sure, then did a little research, and it is in fact external.y balanced. Why did GM decide to go external balance again? I thought internal was better. I know it was probably economics.What changed on a 350 that it was cheaper to balance external?

[1966gmc]

External would be 86 and up. I have a 86 block in mine that requires the balanced flexplate

[allen123]

Oh I forgot to say that i bought another transmission and it still does it so im guessing it just leaves it to the engine

[primered_junk]

Originally Posted by WIDESIDE72

I just learned that the 87 up motors are externally balanced like an old 400. I buddy bought a Ramjet 350 crate motor and he had an external balance flywheel Jeg's recommended. I called them to be sure, then did a little research, and it is in fact external.y balanced. Why did GM decide to go external balance again? I thought internal was better. I know it was probably economics.What changed on a 350 that it was cheaper to balance external?

They went external due to economics, contrary to popular belief, the 305's had a different crank than the 350's, they had the same stroke, but had different counter weights on the crank, and old style 305 crank in a 350 or vice versa will cause a nasty vibration if the rotating assy was not balanced before it was put together. They found a neutral balance for the two and made one crank.

[Green Machine]

87 up 305 or 350 with one piece rear seal, use a weighted flywheel, because the rear of the crank is round, no place to put a weighted flange like the older cranks.