vibration.........from where?????

[americanmusc1e]

something is wrong with my 383. It has a BAD vibration starting at 3000rpm and ending at 3500rpm. this has happened before, and it went away on its own.

It vibrates in Park if you rev the motor up to 3000

I checked the torque converter bolts last time it did this (about a month and a half ago) and they were tight

can a vibration be caused by a misfire?????

it revs past 3500 with no vibration but it doesn't seem to run right. (it revs slow, like it's not running right)


I hope I explained this right. If you have any questions please ask.
thanks in advance for the help

[vectorit]

Had a similar issue, and it turned out the harmonic balancer went bad. Replaced it, all was good again.

[unclewatts]

If you have a bad vibration at a narrow band of RPMs, that is called a resonance vibration. Vectorit could be right, but it could be any number of things such as a loose part somewhere or something in the exhaust system.

[vectorit]

Could be a U joint going bad, or a bent/dented drive shaft as well.

[americanmusc1e]

thanks for the replies, but does anyone know why it would go away and come back.

and could it be caused by a misfire???
I forgot to mention that my tach starts jumping around after 3000 (it's varying by 200-400 rpm), normally it's steady.
OR is it causing a misfire???


on a side note, i took it to my machininst yesterday to because I had a noise like a loose rocker arm (I lost an almost-new engine to an over-tightened rocker arm--I'm a little paranoid sometimes), turned out I had an exhaust leak, but he also said that the motor had a misfire, he told me to do a compression test on it first, and if that looked good, to start checking my iginition system. the problem started on the way home today, after I got home I changed the oil and checked compression on all 8 cylinders, and got 210psi on each.

[americanmusc1e]

Originally Posted by vectorit

Could be a U joint going bad, or a bent/dented drive shaft as well.

it does it in park if I rev the engine, it has to be in the engine or torque converter.

I'll check the torque converter bolts in the morning.

[mikajo39]

Start simple first, Check your plugs, plug wires, ignition timing (sometimes if the dizzy doesn't get tightened all the way timing can vary), carb, vacuum leaks, Don't sweat it too much, and don't worry I'm paranoid as well.

[vectorit]

The tach sounds as though it has a loose connection to the coil.

What kind of fan are you running? If it's a clutch fan, it could be bad. That and check all the blades, and make sure they are solid.

The mis could be causing one hole to not fire long enough to cause some funny business, especially if it is happening on either cyl # 5 or 7. But I'm guessing not. What kind of distributer?

Check everything that rotates off the crank.

[americanmusc1e]

alright, when I did the compression test I left a spark plug wire disconnected,

the engine runs better, and the tach doesn't jump as bad, but....... the tach still jumps around a little after 3000, the engine still has a miss to it, and the vibration is still there.

I would be working on the truck right now, but I have a paper for college that I need to start and finish today, and I shouldn't even be on here right now.

[Classic Heartbeat]

My first Blazer had a vibration when I purchased it because it had a small block 400 in it and the previouse owner installed a 350 harmonic ballancer.
The second time it happened I was down on the Cowletz river on an icy cold winter day steelhead fishing. I drove down there without issues, but when I started it up to return home all hell broke loose!! My engine was vibrating so bad I thought it was going to jump out of the engine compartment!!! I revved the engine up a couple of times seeing if it would clear up and when it didn't I figured I was in for a large tow bill. I went out to see if I could figure out what happened. I popped open the hood and to my suprize there was what looked like bits and pieces of spider webs under my hood, only the web had color to it. It smelled realy bad too!! I scratched my head while I was looking at all this stuff all under my hood, when I looked up toward my fan (witch was hidden by the shroud of coarse) there was a cat woven in and out of my fan blades!! I'll spare you the goary details, but let me tell you it wasn't easy relieving my fan of it.

The third time it happened it turned out to be the flywheel. It had cracked and at certain rpms would vibrate the engine. WES

[mikajo39]

Originally Posted by Classic Heartbeat

My first Blazer had a vibration when I purchased it that turned out to be because it had a small block 400 in it and the previouse owner installed a 350 harmonic ballancer.
The second time it happened I was down on the Cowletz river on an icy cold winter day steelhead fishing. I drove down there without issues, but when I started it up to return home all hell broke loose!! My engine was vibrating so bad I thought it was going to jump out of the engine compartment!!! I revved the engine up a couple of times seeing if it would clear up and when it didn't I figured I was in for a large tow bill. I went out to see if I could figure out what happened. I popped open the hood and to my suprize there was what looked like bits and pieces of spider webs under my hood, only the web had color to it. It smelled realy bad too!! I scratched my head while I was looking at all this stuff all under my hood, when I looked up toward my fan (witch was hidden by the shroud of coarse) there was a cat woven in and out of my fan blades!! I'll spare you the goary details, but let me tell you it wasn't easy relieving my fan of it.

The third time it happened it turned out to be the flywheel. It had cracked and at certain rpms would vibrate the engine. WES

That happened to my dad, darned cats! his galaxie 500 turned it into Cat suey!

[jay6891]

Has this been doing this since the engine was new. Sounds to me like the wrong balancer or bad flywheel. But not a new engine... out on timing?

[americanmusc1e]

Originally Posted by jay6891

Has this been doing this since the engine was new. Sounds to me like the wrong balancer or bad flywheel. But not a new engine... out on timing?

been running the motor for a while now, the vibration just started, although it did do it once before.

[highperf4x4]

It sounds to me like a problem with the harmonic balancer/damper.

Did you use the stock balancer on this truck? They are 2 piece with a rubber cushion between them. I'd check that first.

A broken flywheel will usually make a knocking sound so I'd be surprised if it was that? It could be an issue with the torque converter though.

Your machinist did balance this engine right?

[jay6891]

Also like someone suggested, check your fan blade. I had a bad vibration on my 67 F@rd Fairlane. Threw a blade off the fan. Good Luck Dude!

[americanmusc1e]

Originally Posted by highperf4x4

It sounds to me like a problem with the harmonic balancer/damper.

Did you use the stock balancer on this truck? They are 2 piece with a rubber cushion between them. I'd check that first.

A broken flywheel will usually make a knocking sound so I'd be surprised if it was that? It could be an issue with the torque converter though.

Your machinist did balance this engine right?

yes, the engine is balanced, and I'm using a sbc400 flexplate and balancer.
If it's not anything obvious, its probably in the torque convertor or the 700r4, I've been kicking myself for not keeping the old invincible th350!!!!

[vectorit]

Originally Posted by americanmusc1e

yes, the engine is balanced, and I'm using a sbc400 flexplate and balancer.
If it's not anything obvious, its probably in the torque convertor or the 700r4, I've been kicking myself for not keeping the old invincible th350!!!!

Uh, unless I am mistaken... SBC 400 balancer and fly wheel on anything but a 400 SB is no bueno.

[mikajo39]

Originally Posted by vectorit

Uh, unless I am mistaken... SBC 400 balancer and fly wheel on anything but a 400 SB is no bueno.

Yeah If the engine is internally balanced you really should NOT be running the Sbc400 flexplate and balancer, because the 400sbc were externally balanced, so if ur engine is internally balanced and you are using the externally balanced crap, THERE is your problem! get that stuff off!

[watahyahknow]

its a bit hard with the 400 crank it cant take the 350 stuff because you cant realy balance it internally and cant take the 400 stuff cause its too mush imbalance

they used a rattler or fluiddampr for these aplications but i heared some bad stories bout the fluiddampr one later on .

if the machinist balanced the total rotating assembly (damper crank and flexplate combined) it might be it trown a welded on weight of the flexplate .

the weird stuff the tacho does at 3000 rpm might allso point to a cause maybe the weights in the distributor are loose or theres a vacuumleak or just a crack in the distributor cap
since its happening while not in gear it shuldnt be too hard to hook the engine up to a oldfasion testcase and see wat the ignition does it isnt too invasive on the engine and should rule out the ignition if it isnt the culprit

[highperf4x4]

Originally Posted by vectorit

Uh, unless I am mistaken... SBC 400 balancer and fly wheel on anything but a 400 SB is no bueno.

He's running a 383 with a 400 crankshaft. You need to run the 400 stuff and the machinist needs to balance it correctly. As long as that was done then he's ok.

My question was about whether it was a used 400 balancer or did he get a new one.

[allen123]

I have the exact same vibration except mine is at 2500 to 3000 and i have changed the flywheel, harmonic balancer, made sure it wasnt a bent fan blade, and i cant remember what else i checked but its still doing it, i think the PO of mine just put the motor together without getting it balanced but im gonna be tearing into it pretty soon so i guess we'll find out
I don't know if that helps at all but i have the same vibration i'll let you know what mine is and see if it can help you at all.

[highperf4x4]

Originally Posted by allen123

I have the exact same vibration except mine is at 2500 to 3000 and i have changed the flywheel, harmonic balancer, made sure it wasnt a bent fan blade, and i cant remember what else i checked but its still doing it, i think the PO of mine just put the motor together without getting it balanced but im gonna be tearing into it pretty soon so i guess we'll find out
I don't know if that helps at all but i have the same vibration i'll let you know what mine is and see if it can help you at all.

Yeah but you need to check your crank and see if someone got the 305 crank in there by accident. Your situation sounded typical to me for this.

[bamabaxter]

same vibration.....1500-2500 rpm

[americanmusc1e]

Originally Posted by highperf4x4

He's running a 383 with a 400 crankshaft. You need to run the 400 stuff and the machinist needs to balance it correctly. As long as that was done then he's ok.

My question was about whether it was a used 400 balancer or did he get a new one.

it has a NEW pioneer balancer and flexplate

[elf w/capital T]

well....find it? fix it? what was i?