bad vibration

[philo_beddoe]

It did run smooth after the valve seals, i guess it progressed, it just might not be something that spins and is balanced.

[philo_beddoe]

Vile, all joking aside, three experienced mechanics have failed to identify the problem. I have nowhere else to go, except more mechanics. Know any really good ones in our area, especially with classic chevy engines?

[LTZ C20]

Philo, just bring it on down to American Chevrolet, I'll go on a road test with you first to identify the vibration and then we'll get it fixed up for you in the shop. Haha

[blazer74]

Possible you have a weak or cracked valve spring, considering this started shortly after the valve seal change.

Sure sounds like a miss under load from your descriptions.

 Have you eliminated plugs, wires, cap, rotor, fuel filter?

[Peter S]

Possible you have a weak or cracked valve spring, considering this started shortly after the valve seal change.

Sure sounds like a miss under load from your descriptions.

 Have you eliminated plugs, wires, cap, rotor, fuel filter?

In reply #66 he states that it happens in park or in neutral so there is no load.

[Peter S]

It is my feeling that the harmonic balancer can go bad with age. The outer ring is held in place by rubber which can deteriorate/swell with age and by exposure to heat, oil/chemicals. As this rubber deteriorates the outer ring may shift throwing off the balance.

When we rebuild my son's 350 we found that his balancer had this exact issue. In his case it was very obvious because the outer ring had a considerable wobble which we spotted just by turning the motor over with the starter.

[VileZambonie]

Vile, all joking aside, three experienced mechanics have failed to identify the problem. I have nowhere else to go, except more mechanics. Know any really good ones in our area, especially with classic chevy engines?

You're talking to him

[blazer74]

Uh oh

[blazer74]

It is my feeling that the harmonic balancer can go bad with age. The outer ring is held in place by rubber which can deteriorate/swell with age and by exposure to heat, oil/chemicals. As this rubber deteriorates the outer ring may shift throwing off the balance.

When we rebuild my son's 350 we found that his balancer had this exact issue. In his case it was very obvious because the outer ring had a considerable wobble which we spotted just by turning the motor over with the starter.

Yes I've had the dampener fail on TBird before. In my case it was not driveable tho.

[Greybeard]

Possible you have a weak or cracked valve spring, considering this started shortly after the valve seal change.

Sure sounds like a miss under load from your descriptions.

 Have you eliminated plugs, wires, cap, rotor, fuel filter?

In reply #66 he states that it happens in park or in neutral so there is no load.

This is true, but only under acceleration. The fluid and spinning weight in the tranny is the load, as small as it is.

[philo_beddoe]

Even just going along at 15 mph, you can hear the slight thwoping, like a helicopter, no clanking at all.

Just letting it idle at normal temp in park she runs very smooth, i keep trying to force myself to think its a bad plug/wire, but it just runs to smooth at idle.

I did just notice the smell from tailpipe seemed weird. I had just shut the engine off and was washing salt off the tires and noticed it.

Someone mentioned fuel filter,,how could it be that? Could it?

Oh yeah, when going down the road at say 50 mph, the constant shudder goes away. Then,,,you just hear and feel the hummm-smooth-hummm-smooth-hummmm. About every second it goes from shudder to smooth.

[philo_beddoe]

Vile, all joking aside, three experienced mechanics have failed to identify the problem. I have nowhere else to go, except more mechanics. Know any really good ones in our area, especially with classic chevy engines?

You're talking to him

Ok then, your hired! Im 10 min up the road. I'm comin over saturday with a suitcase full of cash. If you cant figure it out i wont tell anyone, promise.

Can you give me 1/2 hour?

[Greybeard]

Sounds like cabin reverberation to me. It can get really bad in these old trucks.

But that's not it. If it only happened while moving I would say it's a broken belt in a tire. But since it happens in park/neutral sitting still that can't be it either. If it's not between the fan and the tranny oil pump it isn't.  Without pictures it isn't happening....   

[philo_beddoe]

Philo, just bring it on down to American Chevrolet, I'll go on a road test with you first to identify the vibration and then we'll get it fixed up for you in the shop. Haha

On my way bro.....!!!

[philo_beddoe]

Possible you have a weak or cracked valve spring, considering this started shortly after the valve seal change.

Sure sounds like a miss under load from your descriptions.

 Have you eliminated plugs, wires, cap, rotor, fuel filter?

I will be checking every spk plg wire on friday and also cap and rotor,,just for the fun of it.  I did check every plug, all are still clean since i put in when they did the valve seals last fall.