bad vibration

[philo_beddoe]

DNL, i guess it is a 305 right?

[zieg85]

DNL, i guess it is a 305 right?

DNL is a 1979 305... Looks like your mechanic may not know everything so you have a prayer

yes as said already

[philo_beddoe]

Yup' hang on i'll check the vin #'s.

[philo_beddoe]

Hard to tell, might be a different 305.

[zieg85]

numbers matching should have been the last 6 digits of the VIN I thought.  Either way it is a period correct for your truck.  Now to figure out the vibration.  If it is truly RPM related you need to disconnect the torque converter from the flexplate to rule out the rotating mass of the transmission.  It is important to get a tachometer and know where the vibration starts...

[philo_beddoe]

Ok, just got off the phone with a friend, said the same thing. Thats the next thing i will be doing.

[zieg85]

I can tell you my story about my brand new 1996 Nissan pickup.  I needed a back to forth car when I moved back to Indiana from Texas.  I had a 86.5 back in the day before I started getting company cars.  Back to the 96... from day one I had a rpm related vibration which you had to have it under load.  4th or 5th gear and steady speed.  Nissan put new rims, tires, shocks and finally the factory rep came out and took it for a test drive.  Came back and said, that is normal and nothing could be done...  I drove it out of the service bay and went to new car sales and traded it off for another brand new one.  This one I test drove it and it was perfectly fine...  The plus was I got more for it on trade than I bought it for and I went from a plain jane truck to a fully loaded with AC...

[philo_beddoe]

Good trade...

[philo_beddoe]

Heh, my memory just got zapped a little,,,,,,a month ago when i started noticing the engine wasnt running very smooth, i remember when i had the valve seals done, they put on a new dist cap and set the timing to 8 btdc, which i thought was a bit low or retarded. So i decided to just mess with it a little and i loosened dist hold down clamp and turned it to the right thinking i was advancing a little.  And now i see i retarded even more and shortly after thats when i noticed things much worse.

Could this have some effect??

[zieg85]

Heh, my memory just got zapped a little,,,,,,a month ago when i started noticing the engine wasnt running very smooth, i remember when i had the valve seals done, they put on a new dist cap and set the timing to 8 btdc, which i thought was a bit low or retarded. So i decided to just mess with it a little and i loosened dist hold down clamp and turned it to the right thinking i was advancing a little.  And now i see i retarded even more and shortly after thats when i noticed things much worse.

Could this have some effect??

ah, yes... I would now suspect a faulty cap and or wires...  A vintage Sun Machine with the scope would be great right about now

[Rattler12]

You mentioned 383......a 383 is a 350 bored with a 400 crank. All small blocks except the 400 were internally balanced which was balanced externally with the dampener and flexplate/flywheel. Any chance you really have a 400 crank in it with a 305/350 flexplate?

[philo_beddoe]

Not sure on that one rattler, even so, it used to be smooth. I could understand if i had the shudder since the day i bought the truck, but not long ago it was very smooth.

BTW, I turned the dist without disconnecting the vac advance hose. Not sure if that matters or not.

Tonight i will advance the timing properly and see what happens.

[philo_beddoe]

Advancing seemed to make it run better, but not really. I did notice no vac from the little hose though, at idle.

[VileZambonie]

Ok i'll ask,,,whats a cylinder power balance test?

Vile, your pretty savy with these trucks, but i think this one might even stump you.  (Or maybe im just using reverse psychology to get you to invite me over to fix this cursed problem).

Yer funny.

[Greybeard]

You know what that vacuum advance canister looks like so turning the distributor in the direction it points is advancing the timing. Advance the timing a little at time and drive it under load after each time (just tighten the hold down down enough to make it very firm to turn), drive it and listen for knocks or pinging coming from the engine, once you get to that point turn it back until they are gone (under load). Running on the edge of pinging is the sweet spot to start the rest from. If it does not idle smoothly then more tuning needs to be done. But that is another problem it sounds like you don't have if it ran smooth before the valve seals.